Microbiology Exam 3 Study Guide
Microbiology Exam 3 Study Guide MICR 3050
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This 23 page Study Guide was uploaded by Toni Franken on Sunday April 3, 2016. The Study Guide belongs to MICR 3050 at Clemson University taught by Dr. Whitehead in Spring 2016. Since its upload, it has received 110 views. For similar materials see General Microbiology in Microbiology at Clemson University.
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Date Created: 04/03/16
MICR 3050 – Exam 3 Study Guide Dr. Whitehead, Clemson University Exam 3: Chapters 8, 9, 41, and 43 Modeled around Dr. Whitehead’s recommended subjects to study – color coded/organized by power point chapters. Chapter 8: Control of Microorganisms 1. Define the frequently used terms of microbial growth control Sterilization: Absolute destruction or removal of all viable organism. Shouldn’t be able to find endospores, spores, fungi, bacteria, viruses, and more. Nothing should be left living. True Sterilization very rarely happens. Disinfection: Trying to get rid of pathogens – the dangerous bacteria, microorganisms. The killing, inhibition, or removal of pathogenic organisms. o Disinfectants: Agents, usually chemical, used for disinfection, usually done to inanimate objects. Sanitization: Reduction of the overall microbial load – reduction of microbial population to levels deemed safe (based on public health standards). Tends to be inanimate objects. Food industry. Antisepsis: Prevention of infection of living tissues. Antiseptic agents – material you’d put on a wound to prevent infection from occurring. How to decrease microbial load on living tissues. o Antiseptics: Chemical agents that kill or inhibit growth of microorganisms when applied to tissue. Tend to be gentler, because you don’t want to harm living tissue while trying to kill microbes. Chemotherapy (not cancer related): General term is the use of chemicals to kill or inhibit the growth of microorganism within host tissue – Targets microbes inside the body. Antimicrobial Agents: o cide: Cidal agent, bactericides, fungicides, algicides, and viricides. Anything with the suffix –cide will actually kill the microbe you’re targeting – fungicides kill fungi, bactericides kill bacteria, etc. Most antibiotics fall into this category o static: Static agents don’t actually kill what you’re targeting. They simply inhibit the growth of the organisms as long as it is in the presence of the static agent. Bacteriostatic and fungistatic. NOTE: if this static agent is removed, but the microbes aren’t taken care of, the infection may still be established. Some antibiotics fall into this category – used if you’re hoping that bacteria/microbes will be flushed out or handled by the immune system. 2. Describe the pattern of microbial death and how to measure an agent’s killing efficiency (decimal reduction time). Bacteria die in an exponential pattern , just like they grow exponentially. It’s just in the opposite direction. Microorganisms are not killed instantly, and that’s what gives it this pattern. Measure of agent’s killing efficiency: Decimal reduction time (D value) time to kill 90% of the population. What is the problem with this? o We measure this by looking at viable cells. However, there might be nonculturable cells. T There are some microbial control agents that seem to cause bacteria to switch to viable, but nonculturable state. We will never be able to culture them, and they will be counted as dead cells. However, they may still be perfectly capable of causing disease. Can plot the same way as cell growth: Want log scale of cell numbers. However, with graph is only a range of time. By the time you reach the decimal kill (90% population kill), the rate of death has probably changed. The last 10% that is left is possibly made of resistant bacteria that won’t die at the same rate as everything else. 3. Describe the conditions that influence the effectiveness of an antimicrobial agent. Population size: Most antimicrobial agents have an exponential decline in terms of effectiveness. The more cells we start with, the longer it’s going to take for the agent to kill 90%. Population Composition: We have to think of the state of the cells – are they endospore formers? Some strains of bacteria are are resistant to antimicrobial resistance than others. o Stationary phase – probably less susceptible. o Growth phase – probably more susceptible. o What stage are they in? That matters. Concentration or intensity of the agent: Have to think about concentration of the chemical, and where it is most effective. As you increase the concentration of the drug or agent, the efficiency increases. For a number of agents, there is a point at which, the increase of efficiency is going to slow down. o Must also be careful about toxicity to person. o There are some disinfectants that are more effective at lower amounts, such as ethanol. In hand sanitizers, EtOH is very drying, but the mechanism of action through which ethanol kills bacteria is dependent on activity in conjunction with water. 95% ethanol is less effective because there is less water available for it to work with. Duration of Exposure: VERY IMPORTANT – there is usually a duration between which the time you expose the microorganisms to the agent. Typically, the longer you use an agent, the less concentration you need. The less time you expose it, the higher the concentration you need to use. Can be limited by safety of the agent. Temperature: Usually, the higher the temperature, the more effective the antimicrobial agent. Not always true, but is generally the rule. Some cases, you can get away with lower concentration/duration with a higher temperature of exposure. Local Environment: Is the pH neutral or is it acidic? Anytime you can combine stresses, things tend to be more effective. Have to think about all sorts of different environmental factors. 4. Describe the mechanical (filtration) and physical methods to control microorganisms (moist heat, dry heat, low temperature, UV radiation, ionizing radiation). Mechanical Methods: o Most common type is filtration. Filtration can be used for sterilization. Can also be used for basic disinfection. Depends on filter type. Reduces microbial population or sterilizes solutions that are heatsensitive. o Regardless of the method, filtration always uses some plane with very small pores, which keeps microbes from passing through the plane. True sterilization through filtration requires pores that are about .2 micrometers wide. You might use filtration over something else due to the heat sensitivity of medium. o There are two types of filtration: Most common is syringe filter: A filter is placed in a syringe, and then you push liquid through filter. Bottle top: This method can be used for larger amounts. Can also be used for air – surgical masks, HEPA filters (highefficiency particulate air), cotton plugs on culture vessels, laminar flow biological safety cabinets. o Filtration doesn’t have to be overly complex – for a long time, could just put a giant cotton plug in the mouth of the flask. Keeps bacteria out. Physical Methods of Control:Can use heat (moist and dry), low temperature (freezing – probably won’t kill it, but might damage it), and radiation. o Heat: Moist Heat: Destroys bacteria, fungi, and viruses. It degrades nucleic acids, denatures proteins, and disrupts the membranes, which are all vital parts of the cell. Tends to be pretty effective, especially for active cells. Use boiling (won’t destroy endospores, so does not sterilize), autoclaving, and pasteurization. The amount of time to boil something to kill an endospore, either doesn’t exist, or is impractical. Autoclaving – the only method that will be used that allows for actual sterilization. Pasteurization is more so to knock down microbial levels. (NOTE: when saying boiling doesn’t kill spores, talking about bacterial spores. Fungi spores are killed through boiling – eukaryotic spores easier to kill than prokaryotic). NOTE: Bacterial spores can be destroyed with heat combined with pressure. An autoclave is the main way we sterilize medium for microbiological use. Also for glassware. As long as it isn’t heat sensitive or sensitive to water, can sterilize with an autoclave. Have a combo of high pressure and high heat. Heat is made more effective than heat by itself would be. You do have to check every now and again to make sure an autoclave is working. Intentionally autoclave endospores, and see if they will culture and grow. Basically, an autoclave has a very thick wall, creating a closed system. Start with boiling water to produce steam. The air inside the autoclave is pumped out as steam is pumped in. The more steam pumped in, the higher the pressure gets. Also have heaters that are functioning. You get to about 121 degrees C, and about 15 psi. Time is 15 – 20 minutes (12 minutes might only be required, but is sensitive to how much you’re autoclaving). The pressure increases more rapidly than the temperature. As temp and pressure increase, they both reach a plateau, and overlap for a period of time, which is where sterilization occurs. Then, both decrease, where pressure decreases first, followed by temperature. A full autoclave cycle runs for about 45 minutes to allow for temp and pressure increase, sterilization (15 minutes), then returning to normal temp and pressure. Pasteruization: Mostly used in the food industry. Using heat, but tends to be a controlled process. Hold heat at a temperature wellbelow boiling. Milk, chocolate, Guinness all pasteurized. Hold things at temperature that is high enough to kill microbes, but not to damage the food. If you boil milk, it gets an offflavor. The idea is to kill pathogens present and slows spoilage – store food longer and prevent foodborne illness. DOES NOT STERILIZE – just reduces the overall load of the organism present. Dry heat sterilization: Less effective than moist heat sterilization – requires higher temperatures and long exposure times. Items must be subjected to 160 – 170 °C for 2 to 3 hours. C. botulinum – takes 5 minutes with moist heat (autoclave) at 121 °C, whereas with dry heat, requires 2 hours at 150 °C. Works in a different way. Will still denature things, but also have oxidation of cell constituents. This is typically what we do in lab – flaming loops, tube mouths, etc. o Low temperatures: Freezing – stops microbial reproduction due to lack of liquid water – As soon as a frozen item is warmed at room temperature, it allows for the microbes to begin doubling. Some microorganisms killed by ice due to crystal disruption of cell membranes. Refrigeration – slows microbial growth and reproduction. Does not tend to kill them. There are even some bacteria that can replicate rapidly at refrigerated temperatures. o Ultraviolet (UV) Radiation: Most bactericidal wavelength is 260 nm. Causes thymine dimers in DNA. It is limited to surface sterilization – does not penetrate glass, plastic, dirt films, etc. Very effective, and it doesn’t stick around. Irradiation of food is considered safe. Incorrect pairing the in the DNA prevents replication/transcription. Really good at sterilizing air, and surfaces of things. But it doesn’t get below the surface since it is lowlevel radiation. Can’t get through liquids, can’t get through glass or plastic, etc. o Ionizing Radiation: Agent that penetrates deep into objects. Enough energy that allows electrons to free that creates chemically reactive species that can then destroy things, including microbes. This is used for radiation permeation – use for heat sensitivity or sensitivity to water. Antibiotics are often sterilized this way. Called cold sterilization. Chapter 9: Control of Microorganisms 1. Define antimicrobial, antibiotic, synthetic chemotherapeutic agent, and semisynthetic chemotherapeutic agent. All came about due to the discovery of Alexander Flemming. He had poor aseptic technique, and discovered a fungal contamination that inhibited or killed the growth of bacteria – penicillin. He could not isolate it, others did that. Saved many people during WWII. Antimicrobial Agents: o cide: Cidal agent, bactericides, fungicides, algicides, and viricides. Anything with the suffix –cide will actually kill the microbe you’re targeting – fungicides kill fungi, bactericides kill bacteria, etc. Most antibiotics fall into this category o static: Static agents don’t actually kill what you’re targeting. They simply inhibit the growth of the organisms as long as it is in the presence of the static agent. Bacteriostatic and fungistatic. NOTE: if this static agent is removed, but the microbes aren’t taken care of, the infection may still be established. Some antibiotics fall into this category – used if you’re hoping that bacteria/microbes will be flushed out or handled by the immune system. Chemotherapeutic Agents: Chemical agents (antimicrobials) used to treat disease by destroying pathogenic microbes or inhibiting their growth within a host. Book definition of antibiotic: Microbial products or their derivatives that kill susceptible microbes or inhibit their growth – ex. Penicillin, streptomycin. Something that one microbe produces that kills others. However, this is very specific, and isn’t how the term antibiotic is usually used. o Note: Some antibiotics that we have isolated, they are naturally produced, and we have nothing to do with their creation. We have synthetics and semisynthetics (book calls them chemotherapeutic agents, but everyone calls them antibiotics as well). Synthetics: Sulfa drugs – designed in a lab, produced entirely synthetically. Semisynthetics: Combination of naturally produced compounds and synthesized things. Cases where we took a natural compound and altered it to specify the target, or make it more effective. Ampicillin and amoxicillin are semisynthetic derivatives of penicillin. Harder to break down microbes. More effective at killing microbes. 2. Know and describe the general characteristics of antimicrobial drugs including the terms used to describe their action, spectrum of activity, and their effectiveness. Selective toxicity: Ability of drug to kill or inhibit a pathogen while damaging the host as little as possible. See more information in question o The therapeutic index is the ratio of the toxic dose to your therapeutic dose – want a large number. The bigger the number, the bigger the difference between the toxic dose and the therapeutic dose. Toxic dose will harm the human. The therapeutic dose is the one that is effective to kill the bacteria. Want the biggest difference possible between these two values. For example, have a therapeutic dose of 50 Micromolar, and we won’t see bad effects until 200 micromolar. This is a therapeutic dose of 4. Less risk than a drug with a lower therapeutic dose. Less concern of sideeffects. Narrowspectrum drugs: Drugs that only work on certain classes or types of bacteria – there are drugs that only target gramnegative, spore forming bacteria. You want to treat the most narrow range of organisms possible, but have to know what the infectious agent is. Broadspectrum drugs: Targets a larger range of organisms. cidal agent – kills static agent – keeps them from growing further. Once it is removed, the bacteria can grow again. o Have to look generally at what the drug is targeting – bacteria, protists, fungi, viral agents, etc. o Looking at total cell count versus viable cell count: Bacteriostatic drugs (keep bacteria from growing): Total cell count is leveled off, as well as the viable cell count, and there is no drop off of the cell numbers. We usually rely on another system to actually eliminate the infectious agent. Bacteriocidal: Drug that is killing viable cells, but not causing lysis. The total cell numbers just level off, can’t differentiate between live versus dead with total cell numbers. If you actually look at viable cell numbers, you see a declining number of viable cells. Bacteriocidal (bacteriolytic) with lysis: The total cell count AND viable cell count drop off rapidly due to the application of bacteriocidal agents. 3. Explain how antimicrobials are classified. There are five general classes as far as how antibiotics work: o Inhibit cell wall synthesis – cell wall is primarily made of peptidoglycan, so many drugs will target peptidoglycan synthesis – Vancomycin, Penicillins, Cephalosporins, etc. All inhibit cell wall synthesis. o Disrupt the plasma membrane – not many at all. How would the drug actually get to the target site? Gram positives have to get all the way through the peptidoglycan layer (thick) and gram negatives have to get through outer membrane and cell wall. Not many – Polymyxins. o ProteinSynthesis Inhibitors – Can target any aspect of protein synthesis – can bind rRNA, ribosomal subunits, etc. Tetracyclines, Kanamycin, Erythromycin, etc. o Nucleic Acid synthesis inhibitors – These guys shut down DNA replication or transcription (RNA production). These include DNA gyrase targeters, such as ciprofloxacin. RNA polymerase such as Rifampin, or RNA elongation (Actinomycin). o Metabolic Antagonists – Cover basically any of the bases the first four didn’t cover. They simply interrupt some aspect of necessary cellular metabolism, some metabolic pathway. May be any different metabolic pathway. If you can shut down a vital part of metabolism, you can shut down the cell. The most common are those that inhibit folic acid synthesis (Trimethorprim Sulfanomides). o NOTE: DO NOT HAVE TO MEMORIZE CHARTS!!!! Mostly for your curiosity. 4. Know the mode of action, effect (static or cidal), and spectrum of activity for the following antimicrobials: penicillin, ciprofloxacin, erythromycin, and sulfonamide. Penicillin : Inhibits cell wall synthesis, and is a bacteriocidal agent (kills cells). It will inhibit the crosslinking between peptidoglycan strands. It is dependent on being able to inhibit synthesis of peptidoglycan. Cells must be actively growing for penicillin to be effective – if not growing, peptidoglycan isn’t even being made, so it can’t be inhibited. Relatively narrow – targets most grampositives. Not overly narrow. o Ampicillin, a penicillin derivative, has a much broader range of activity than penicillin itself. It is a semisynthetic. Ciprofloxacin: Inhibits nucleic acid synthesis – bacteriocidal (kills cells) – targets DNA gyrase and topoisomerase – inhibits DNA replication. Technically it is somewhat narrow – more effective against gramnegatives than grampositives, but is used against them, also. Not overly narrow Erythromycin: Proteinsynthesis inhibitor – bacteriostatic (keeps cells from growing, relies on another agent to keep it under control, or the immune system). Binds to ribosomal RNA (rRNA), which inhibits translation. This is a broadrange agent, and is active against many grampositives and some gramnegatives, doesn’t matter the manner of respiration. Sulfonamide: Metabolic antagonists – bacteriostatic (keeps cells from growing, relies on another agent to keep it under control) – has a pretty broad spectrum of activity. Can mimic one of the compounds used in folic acid synthesis and shut down the pathway. 5. Understand the terms related to antimicrobial activity (minimum inhibitory concentration, minimum lethal concentration, zone of inhibition). Minimal inhibitory concentration (MIC) – the lowest concentration of drug that inhibits growth of pathogen. Minimal lethal concentration (MLC) lowest concentration of drug that kills pathogen Zone of Inhibition: In a KirbyBauer test, the size of the zone of inhibition indicates the degree of sensitivity of bacteria to a drug. In general, a bigger area of bacteriafree media surrounding an antibiotic disk means the bacteria are more sensitive to the drug the disk contains. 6. Describe the factors that influence the effectiveness of antimicrobial drugs: Ability of drug to reach site of infection: If there is a pathogen that causes necrosis (tissue death), and its mode of transportation is by the blood stream, the antimicrobial agent might not be able to effectively get to the site due to death of the blood vessels. Mode of administration: Oral administration, IV administration, topical. Oral administration is often the most convenient and cheapest, but may not be the most effective for the drug in question. Susceptibility of pathogen to drug: Do the pathogens in questions have resistance to a drug you’re using? Ability of drug to reach concentrations in body that exceed MIC of pathogen: Can the drug, safely, reach the MIC (see question 5) to help the body fight off the infection? 7. Explain the emergence of antimicrobial (drug) resistant bacteria, the mechanisms of bacterial resistance, the origin and transmission of drug resistance, and ways to prevent it. Once resistance originates in a bacterial population it can be transmitted to other bacteria. A particular type of resistance mechanism is not confined to a single class of drugs. Then, erroneous practices select for the growth of resistant bacteria, making the problem worse. Antimicrobial drug resistance is NOT a new concept – it began almost immediately after the introduction of penicillin, showing the adaptation of the microorganisms. However, resistance development can be increased due to human practices. o Origin of Resistance: Natural immunity genes Spontaneous mutations o Location of resistance genes Chromosome Plasmids (R factors) Transposons (jumping genes) Gene cassettes and integrons Methods of Bacterial Resistance: o Preventing entrance: The bacteria may be able to keep the drug from entering the cell entirely – capsules may be one method. o Efflux pumps: Organisms may be able to pump detrimental drugs out of the cell back into the environment, preventing damage done to the cell. o Inactivation: Some bacteria may be able to inactivate the drug that is targeting them with their own products or actions. o Target modification: May be able to modify the portion of itself that the drug is targeting. If the target no longer exists as expected, the drug may have a hard time finding what it is supposed to attack. o Alternate pathway: Some drugs target specific pathways in bacteria. So, some organisms are able to use an alternate pathway to continue to produce the item they need, even if the drug inhibits another pathway. Transmission of Resistance: o Horizontal gene transfer: Transfer of genetic material between organisms in the same generation. Transformation – organism may pick up resistance DNA from the environment. Conjugation – one organism may give another organism resistance genetic material through a sex pilus. Transduction – a viral vector may carry resistance genes from one bacteria to another, passing along the resistance. Preventing Transmission of Resistance Microbes: o Give drug in high concentrations to destroy all susceptible organisms – if you eliminate the entire population, you eliminate the possibility of resistance transfer. o Give two or more drugs at same time – The idea that if one drug doesn’t take care of the resistant population, the other might. o Use antimicrobials only when necessary – DO NOT use antibiotics for a common cold, which is a virus. Overuse only encourages the resistance development. o Take full course of antimicrobial – Many people do not take the full course of the antibiotic they are given. They often feel better part way through the dosage, so they don’t eliminate the entire population when they stop treatment early. This selects for resistance bacteria to thrive and replicate. o Use narrow spectrum antimicrobials the more narrow a drug’s target is, the less likely it will affect other microorganisms to cause development of resistance. o Continued development of new antimicrobials – In the recent years, the development of antibiotics and antimicrobials has decreased dramatically. New research needs to be done to continue developing new drugs. o Use of bacteriophages to treat bacterial disease – An emerging idea that the use of viral agents, bacteriophages, could be used instead of antibiotics and other antimicrobial drugs to help reduce resistance. Not high supported at this time. Chapter 41: Microbiology of Food 1. Describe the intrinsic and extrinsic factors that control the growth of microorganisms in food. Food composition and spoilage – composition is an intrinsic factor: Carbohydrates: High carbohydrates cause mold predomination and contains little odor. Ergotism – disease caused by Claviceps purpurea toxins – fungus or mold that is known to get into grains, and subsequently flour. Spoilage caused by molds or fungi are more visually identified. Very little odor. Ergotism: Entire populations of people in history have suffered with this illness. Can have altered behaviors, suffer from hallucinations, lead to spontaneous abortions, and can kill you. One theory of the Salem Witch Trials was massive numbers of Ergotism in that area. The toxin related to Ergotism is very closely related to the active ingredient in LSD. There are a number of migraine medication that are based on this toxin. Cafergot (medication) Proteins or Fats: Bacterial growth predominates; foul odors. Has putrefaction – anaerobic breakdown of proteins. Foulsmelling amine compounds are produced. Bacteria that are really good at metabolizing proteins and fats are especially odiferous. There are some compounds produced called cadaverine and putricine. Intrinsic Factors in general: pH, presence and availability of water, oxidationreduction potential, physical structure, antimicrobial substances. If you have a food that is acidic, you’re less likely to have bacterial contamination (molds and yeasts grow better in acidic foods). Neutral or more basic tend to harbor more bacterial contamination. Presence of water – (lower amount of water more so seen with mold contamination/fungi). Fungal contaminations require more water. Have to think about redox potential – liklihoood that there are electron receptors in food that microbes could use. Cooking makes it harder for bacteria to find electron acceptors. Physical structure of food – ground beef versus steak. Think about surface area. Some food also contains natural antimicrobials. Certain spices have very potent antimicrobial activity. Garlic coes, also (allicin). Coumarins found in certain frutis and vegetables. Lysozyme found in tears, saliva, and also found in egg whites. Extrinsic Factors: Easier to control. Typically things we do to food. Heating – can kill large numbers of microbes. Cooling stops or slows their growth. Humidity – for the most part, if you reduce available water to bacteria, it will reduce microbial growth. Atmosphere is also important – absence of oxygen inside canned goods, eliminated the possibility for all aerobic organisms to grow. Have basic concept of modified atmosphere packaging – try to reduce oxygen in packaging of food – shrink wrap, cling wrap, vacuum technologies. 2. Describe food spoilage and how foods can be preserved Food preservation: The idea is not to sterilize the food. We’re normally just trying to decrease microbial loads to reduce spoilage and prevent illness. Could filter food, but the main focus of preservation has to do with temperature. Food storage is at low temperatures. High temperatures is based on killing microbes. Canning uses high heat to kill, and also eliminates oxygen to eliminate a number of human pathogens. o Canning: What you’re combining is heat, sometimes a little bit of pressure, and an anaerobic atmosphere. It does not sterilize food, and does not effectively kill endospores. Spoilage of commercially canned foods is rare. The reason people say not to eat dented canned food is that microbes could have gotten in if there was a breach. Fermenters would be the microbes that could survive in a sealed can – produce CO 2 d gaseous forms of hydrogen sulfide. If you have an extreme example of this, you can get enough gas production to cause bulging from a can. Spoilage associated with canning is almost always involved with a mistake being made. Much more common to see issues from homecanned foods, and non acidic canned foods. o Pasteurization: Purpose is not to sterilize, just used to try to get rid of pathogens that could cause disease, and reduce the overall microbial load. Helps prevent spoilage and preventing foodborne illness. Before pasteurization, many people god tuberculosis from drinking unpasteurized milk. Mycobacterium bovis – at one time, was a relatively large cause of TB in the past. There is an inverse relationship between time and temperature used to pasteurize food. Longer time you use, the lower temperature you can use. Shorter temperature, lower time. Some foods cannot be heated to a higher temperature without ruining the value of food. Chocolate tends to be more gently pasteurized. Low temperature holding (LTH) – 63 DEGREES c for 30 minutes. High Temperature Short time (HTST) o Reduction of available water: Fungi are more tolerant to low water levels (ex: moldy bread), while most microbes need a high amount of water. Halophilic bacteria don’t follow this trend. These are rare. Can do this through dehydration or the addition of solutes (salt or sugar curing). Both reduce available water. There are also chemically based preservatives. A number of these work to try to damage microbes. Very tightly regulated – any chemical based preservative has to have “GRAS status” aka safe. Some concerns about what these preservatives can do inside the body. Concern is that they’ll react with compounds in your body to create possible carcinogens. o Radiation: Radappertization – use of ionizing radionation (gamma radiation) to extend shelf life of food. Causes peroxidation of water. This could be used to sterilize food. Sometimes used for very longterm storage. 3. Compare and contrast food infection and food intoxication. Be able to categorize the disease causing foodborne microorganisms that were discussed into the appropriate category. Food infection: Pathogenic organism is present in the contaminated food when ingested. o Process: Food is infected with a pathogen, you ingest the food, and the pathogen manages to grow inside your body. o The Problem: Any number of things can happen while it is growing, such as toxin production, tissue invasion, etc. The key to the infection definition is that the pathogen must actively grow inside your body. Typically takes 12 hours or so to appear – relatively long incubation time – Incubation time: time from when you’re exposed to time when symptoms appear. It takes time for the pathogen to grow to amounts that cause the symptoms. Many types of food infection can be treated with antibiotics because it is based on the presence of actively growing bacteria. There are some exceptions where antibiotics make the infection worse, but those are few and far between. Food intoxication: Pathogens were present in the food at some point, but they aren’t the causative agent of illness. The residual toxins from their presence are. o Process: At one point in time, there was a pathogen in the food. While it was in the food, it produced large amounts off the toxin, which do not deteriorate. o The Problem: You ingest the food that contains the toxins, and as soon as those toxins cause their damage, you’re going to be exhibiting symptoms. Usually takes less than 12 hours, sometimes even as short as 3 or 4 hours. Because there are no actively growing bacteria, antibiotics won’t work. Toxins cause the damage. o Common treatment is antitoxin – where you actually give person a substance that will bind to the toxin and prevent it from having its action. NOTE: Toxins can be involved in both cases! Big difference is the presence or absence of actively growing organisms. 4. Be able to identify the causative organism of a foodborne illness based on the general characteristics of the microbe, its sources, how it causes disease (toxins, etc.), the characteristic symptoms of the disease, the individuals that are susceptible, the foods involved, and/or the mishandling of the food that lead to the illness. Listeria monocytogenes: Food Infection o Gram positive o Facultative aerobe grows in any oxygen conditions, but prefers oxygen heavy environments. o Coccobacillus very short rod. o Psychrotolerant – tolerant of cold temperatures, so refrigeration doesn’t help. o Characteristics: It is also acid tolerant and salttolerant. Can grow at refrigerator temperatures, and does so effectively. This is not the optimum temperature, but it can still thrive. Contaminated food, if left directly on the shelves of the refrigerator, can transfer organisms there, which can subsequently contaminate the next item placed there. Can be found in fecal material of warmblooded animals, as well as soil, water, vegetation, or silage (fermented grain fed to livestock). Produce is open for contamination by listeria. o Largest Problem: It can grow almost anywhere in the body it wants to go, ranging from the GI system, where it can then leave from to cause infections of the blood stream, causing meningitis (which has high rates of mortality), and is one of the few organisms that can cross the placental barrier where it can cause miscarriage or stillbirth. This is why pregnant women are told to not eat deli meat, unpasteurized dairy products, etc. High rates of hospitalization. Infectious dose is about 1000 bacteria. Listeria was involved in the largest meat recall we’ve ever had (deli meats and hot dogs) in 2002. It was the recall of almost 30 million pounds of meat. There was also a cantaloupe outbreak in 2011, which was the deadliest foodborne outbreak that the US had seen in the over 100 years. 147 people got sick, 142 hospitalized, about 20% mortality rate. o Almost always causes food infection. Classic GI symptoms will probably occur within the first 24 hours. Onset is a few days to 2 months, however, for other symptoms, such as fever, muscle aches, nausea, diarrhea, meningitis, confusion, loss of balance, and miscarriage. The duration of illness is usually about 5 – 10 days WITHOUT further complications. People at most risk (for severe complications) are pregnant women, children less than a year old, and individuals over 65 years old (considered elderly) due to low immune efficiency. Tends to be fatal through comorbidity (more than one illness involved in elderly patients). People that are immunocompromised due to illness or medications are also heavily at risk. o Foods it commonly passes in are uncooked meat and vegetables, fruits, processed foods, unpasteurized milk, and milk products. Atrisk people should not eat soft cheeses, refrigerated smoked meats, deli meats, and undercooked hot dogs. o PSYCHROTOLERANT AND VERY INVASIVE (LEAVES THE GI TRACT). These are the characteristics that make Listeria very dangerous. Salmonella: Food Infection o Gram negative o Rod bacillus o Facultative aerobe o Major sources: Fecal contamination Big problem with Salmonella getting inside of eggs due to infected ovaries of birds. Small reptiles commonly carry salmonella. Foods that are commonly infected include beef, pork, fruits, veggies, eggs (custards, cakes, pies, eggnog), and dairy, products. o Salmonella cases stay relatively steady throughout the year, except for the occasional large outbreak. Caused by food infection, but commonly expressed as gastroenteritis (salmonellosis). Gastroenteritis: Infection of GI tract where cells multiply and colonize in the GI tract. Cellassociated endotoxins are responsible for symptoms. Infectious dose – at least 1000 viable cells (generally), but this is up for debate due to variety of salmonella and host factors. Highly survivable – most people don’t need medical intervention. Endotoxins: Wide range of toxins may be produced by microbes. Exotoxins are toxins that organisms secrete into the environment. These toxins are typically proteinaceous, and secreted by the organism that makes them. LPS (lipopolysaccharides) is a typical toxin. The immune system will respond to it. Escherichia coli : Pathogenic E. coli (many strains of E. coli exist some are used as probiotics, and some are commensal and don’t cause us harm, others are pathogenic and cause illness). Food Infection. o Gram negative o Facultative aerobe o Typically rod shaped, but there are certain strains and conditions that result in a coccobacillus shape. o Source: Almost all contamination results from fecal contamination from a variety of animals. Different strains of E. coli cause different kinds of disease. Example Categories: ETEC – Enterotoxigenic – traveler’s diarrhea. Comes from contamination drinking water. It is a Nonshigatoxin producing organism. Tends to be selflimiting and doesn’t need medical attention. EHEC or ESTEC – Enterohemorrhagic – bloody diarrhea. Comes from undercooked ground beef, unpasteurized dairy products and fruit juices, spinach, and water. It is shiga toxin producing. Medical attention requirement depends on if complications arise or not. o E. coli O157:H7 (food infection) – most common type of EHEC. Leading cause of kidney failure in children. Has an incredibly low infectious dose (10 cells or less). Produces toxins – Shiga toxin for sure, which causes hemorrhagic colitis (severe inflammation of the colon that often leads to bleeding) and hemolytic uremic syndrome (HUS). HUS is the complication that kills people, where shiga toxin destroys and damages blood cells, which leads to clots. In the kidneys, there are very small, numerous blood vessels. If clots get into these vessels, it causes kidney damage, and eventually kidney failure. May often hear of dialyses to help with kidney damage. Bacteria will be destroyed by proper heat treatment of food. Symptoms appear in 3 – 5 days, and will result in bloody stools, intense abdominal pain, fever and vomiting are rare, kidney failure, brain damage, and death. Duration is about 5 – 10 days. Lower mortality rate than Listeria. Staphylococcus aureus : Food Intoxication o Gram Positive o Coccus o Facultative Aerobe o Tolerant to high salt content o While it is capable of being a foodborne problem, it is also capable of causing a number of other infections. Most common type are skin infections, but this discussion involves foodborne staph. Unlike things like salmonella and listeria, the main place staph comes from is from people. Anytime you have staphborne illness, there has typically a breakdown in hygiene protocol. 25% of the population of humans are a carrier of staph, meaning they are unaffected by the infection. A lower percentage of individuals carry staph on their skin, most carriers have it in their nose. The biggest problem with staph carriers is that they shed staph routinely. o Enterotoxin producer – type of exotoxin. Something secreted by the organism. Staph produces a number of toxins – only a number cause issues in foodborne disease. The toxin is very heat stable and resistant to digestive proteases in saliva or stomach fluids. o The foods it is found in it vary widely – often seen in creamfilled baked goods, poultry, meat, gravies, egg and meat salads, puddings, veggies. Tends to be starch heavy foods that have issues. In food problems, staph is an intoxication. o Common scenario of contamination – food gets contaminated while being prepared, and then sits out for a period of time (room temp, potluck, picnic, etc.). The staph organisms grow, and the toxin builds up. o Symptoms: Rapid onset (1 – 8 hours) – nausea, explosive vomiting, abdominal pain, diarrhea, headache, weakness, no fever (usually subnormal body temperature). Duration is about 1 – 2 days. Clostridium botulinum : Food Intoxication o Gram positive o Rodshaped bacteria o Spore formation o Strict anaerobe. CANNOT grow in the presence of oxygen. Oxygen may trigger spore formation. o Sources: Naturally found in soil and water. Honey is a common source. o Different types of diseases can be caused by clostridium botulinum – some are intoxications, some are infections. Wound botulism: Someone gets wounded, and botulism got into it. This is an infection. See a few cases in the US, and commonly associated with IV use. Infant botulism: An active infection, and usually results from a baby eating something that contains botulism spores. The spores germinate in the baby’s GI tract, and cause an infection. Adults are not as susceptible to these spores. Microbes in the GI tract have colonization resistance, which keeps you from getting sick from pathogenic microbes ingested from food. Endospores are not destroyed by baking, so baked goods with honey in them are also possible carriers. Foodborne botulism: An intoxication – someone consumes food that contains a large amount of botulinum toxin in it. Single most toxic product that we know of, and it is an exotoxin. It is very sensitive to heat, though, and in theory you can destroy the toxin by boiling for 10 minutes. Intoxication usually occurs from improper cooking. We usually see this intoxication in nonacid homecanned vegetables like corn/beans/smoked and fresh fish. Usually occurs from eating food that are not cooked. 10% of contamination issues in canned goods comes from industrial canned, and 75% comes from homecanned. o Adults should not be susceptible to botulism infection in most cases o Symptoms: Onset is in 12 – 72 hours, blurred vision, dizziness, cramps, vomiting, no fever, nausea, constipation, heart paralysis, difficulty in swallowing, speaking and breathing. Most severe and fatal issue is the inability to breathe properly. In babies, it presents differently, and is usually seen as severe constipation. Duration of the intoxication is heavily dependent on how quickly you get treated with an antitoxin. This antitoxin is made of preformed antibodies that can bind to the toxin and prevent it from having its effects. The mortality rate for botulism before the antitoxin was about 50%, and now it is somewhere around 5%. If you have an outbreak of botulinum intoxication, the first person has a much higher mortality rate. 5. Describe other foodborne infectious diseases that are not caused by bacteria. Most foodborne infections are thought to be caused by viruses. Typically have to treat with rehydration more than anything. Symptoms for most viral infections are gastroenteritis (swelling/inflammation of GI tract), which is accompanied by diarrhea, nausea, and vomiting. Recovery is spontaneous and rapid (usually within 24 – 48 hours). Usually self limiting. Primary agents are noroviruses: Also have rotavirus (number of cases has declined substantially since the introduction of rotovirus vaccines – every child is vaccinated against it), astrovirus, and hepatitis A. Food borne Protozoan diseases: o Giardia lamblia, Cryptosporidium parvum, and Cyclospora cayetanensis can be spread via food. Typically due to contamination by fecal matter in untreated water that is used to wash, irrigate, or spray crops, and via drinking water. Foods usually involved are fresh foods (fruit, veggies). o Toxoplasma gondii is a protozoan spread through cat feces or undercooked meat (often pork) – prenatal infection can cause blindness and stillbirth. The most common cause, however, is pork that is undercooked. Toxo tends to reside in the brain, but many people that have it don’t exhibit symptoms. In rodents, this brain infection causes “zombie” rodents. Toxo can only fully complete its life cycle in cats. Main thing that cats eat – rodents and birds – so we often see toxoplasmosis infection in rodents. Rodents infected with toxo lose their fear of cats, which allows the transfer of the protozoa. It was found that the parasite alters the response of rats to cat urine – instead of being fearful of the smell of cat urine, cat urine lights up the part of the brain that lights up a positive response to a potential mate. T. gondii has also been studied for other effects on the brain. They suggest that infected individuals are more extroverted, more likely to get into car accidents (shown by numerous studies). There is a lot of controversy about whether there is any relationship between schitzophrenia and T. gondii infections. Yet, this has not been really shown. Prion based diseases: Incredibly stressresistant and infectious proteins. They are infectious agents made of proteins that cause disruption in neural tissue. We have nothing that can treat prionbased diseases. Nothing has shown any level of slowing down disease progression, or treatment. Symptoms are usually neurological – depression, loss of motor coordination, dementia, death. o Spongiform encephalopathy. o Main type of prion disease is vCJD linked to consumption of meat products from cattle afflicted with BSE (mad cow disease). Beef contaminated with a prion is not safe to consume – nothing can be done to make it safe for consumption. Appeared to stop the development of new cases of BSE. No longer using cow brains as animal byproduct. 6. Distinguish between safe and unsafe food practices. o There are many protocols now in place to help prevent foodborne illness. o Keep things clean (wash hands, and surfaces, wash raw fruits and veggies). o Separate – don’t crosscontaminate (meat on different cutting board). o Cook to proper temperatures. o Chill – refrigerate promptly. Always refrigerate food that is perishable within 2 hours. (1 hour when temp is over 90 degrees outside). o Use cooked leftovers within 4 days. o CDC says that water is usually fine alone to use to clean foods. Look at the surface of the fruit – rough needs more scrubbing, smooth doesn’t take much. 7. Understand the role of fermentation in food production, and be able to recognize various fermented foods. Some food that undergo fermentation: Dairy products, meat products, vegetables and vegetable products, yeast bread, chocolate. Wine and beer production. Humans have been utilizing fermentation for food for centuries, if not thousands of years. Evidence as early as 6000 B.C. Many dairy products undergo fermentation such as yogurt and cheese, as do veggies like pickles and kimchee. The primary organisms in dairy food fermentation are Lactococcus and Lactobacillus, as well as Streptococcus thermophiles. In soy sauce, aspergillus (a fungus) might be used. Most common organisms are lactic acid fermenters. Fermented milk products include buttermilk, yogurt, cheeses, etc. Most of these are created using lactic acid bacteria (Lactobacillus, Lactococcus, Leuconostoc, and Streptococcus). o The main characteristic of lactic acid fermenters is the production of lactic acid. Can divide into two groups: Homofermenters (only produce lactic acid) Heterofermenters (mainly produce lactic acid, but also produce carbon dioxide and ethanol). There are several unifying characteristics of lactic acid producing organisms: All are gram positive. They are acid tolerant, nonspore forming, aerotolerant, and fermenting. Most of the organisms, especially the Lactobacillus and Lactococcus, are considered beneficial organisms. So, rather than causing illness, have beneficial sideeffects to the host. Only time they cause issues is if they get into the blood stream. Largely where the idea of probiotics comes from. 8. Define probiotics and describe their health benefits. What microbes are most commonly used as probiotics? May be able to intentionally inoculate yourself with certain types of bacteria that are beneficial. Can take a pill or eat a particular food that contains beneficial microbes. Basics of the definition: Live microorganisms are contained in these items, and in adequate amounts, confer a health benefit to the host (Lactobacillus and Bifidobacterium are some common types). o The problem with probiotics is that they are not regulated by the FDA. If they tell you certain numbers of bacteria, or certain types of bacteria, are contained in an item, they might not actually be true. Probiotics MUST be a live microbe. It can be any number of bacteria, and there are some yeast species that classify as probiotics. Take that microbe, and give it in an adequate amount, there will be a health benefit. This is a poor definition – don’t know adequate amounts. Most probiotics don’t actually come out
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