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BSC242 week of 3/21 notes

by: Alexandra

BSC242 week of 3/21 notes BSC 242

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Ch 14 (principles of disease and epidemiology) and Ch 15 (microbial mechanisms of pathogenicity)
Microbiology and Man
Daryl W. Lam
Class Notes
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This 13 page Class Notes was uploaded by Alexandra on Thursday March 24, 2016. The Class Notes belongs to BSC 242 at University of Alabama - Tuscaloosa taught by Daryl W. Lam in Winter 2016. Since its upload, it has received 19 views. For similar materials see Microbiology and Man in Biology at University of Alabama - Tuscaloosa.


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Date Created: 03/24/16
Ch 14 Principles of Disease and Epidemiology Pathology The study of disease Disease An abnormal state in which the body is not functioning normally Etiology The study of the cause of a disease Pathogenesis The development of disease Infection Colonization of the body by pathogens Normal Microbiota and the Host Normal microbiota Permanently colonize the host Transient microbiota May be present for days, weeks, or months Symbiosis Is the relationship between normal microbiota and the host Factors determining the distribution and composition of the normal microbiota  Nutrients  Physical and chemical factors  Defense of the host  Mechanical factors Symbiosis Commensalism One organism benefits and the other is unaffected Mutualism Both organisms benefit Parasitism One organism benefits at the expense of the other Some normal microbiota are opportunistic pathogens Locations of normal microbiota on and in the human body  Eyes  Mouth  Skin  Nose and throat  Large intestine  Urinary and reproductive systems Microbial antagonism Is a competitive between microbes Normal microbiota Protect the host by  Occupying niches that pathogens might occupy  Producing acids  Producing bacteriocins (protein based toxins) Probiotics Live microbes applied to or ingested into the body, intended to exert a beneficial effect Koch’s Postulates (used to prove cause of infectious disease) 1. The same pathogen must be present in every case of the disease 2. Pathogen must be isolated from the diseased host and grown in pure culture 3. Pathogen from the pure culture must cause the disease when it is inoculated into a healthy, susceptible laboratory animal 4. Pathogen must be isolated from the inoculated animal and must be shown to be the original organism Koch’s Postulate scenario 1. Microorganisms are isolated from a diseased or dead animal 2. Microorganisms are grown in pure culture a. Microorganisms are identified 3. Microorganisms are injected into a healthy laboratory animal 4. Disease is reproduced in a laboratory animal 5. Microorganisms are isolated from this animal and grown in pure culture a. Microorganisms are identified i. Microorganisms from the diseased host caused the same disease in a laboratory host Koch’s Postulate  Some pathogens can cause several disease conditions  Some pathogens cause disease only in humans Classifying Infectious Diseases Symptom A change in body function that is felt by a patient as a result of disease Sign A change in a body that can be measured or observed as a result of disease Syndrome A specific group of signs and symptoms that accompany a disease Communicable disease Disease that is spread from 1 host to another  Chicken pox  Measles  Genital herpes  Typhoid fever Contagious disease Disease that is easily spread from 1 host to another  Chicken pox  Measles Noncommunicable disease Disease that is not transmitted from 1 host to another  tetanus Occurrence of a Disease Incidence Fraction of population that contracts a disease during specific time It is an indicator of spread of the disease Prevalence Fraction of population having a specific disease at a given time, regardless of when it first appeared Sporadic disease Disease that occurs occasionally in population Ex: typhoid fever Endemic disease Disease constantly present in a population  common cold Epidemic disease Disease acquired by any hosts in given area in short time  influenza Pandemic Worldwide epidemic  AIDS  Influenza at times Herd immunity Immunity in most of a population Severity or Duration of Disease Acute disease Symptoms develop rapidly and last short time  Influenza Chronic disease Disease develops slowly  Tuberculosis  Hepatitis B Subacute disease Symptoms between acute and chronic  Subacute sclerosing panencephalitis (rare brain disease) Latent disease Disease with a period of no symptoms when the causative agent is inactive  shingles Extent of Host Involvement Local infection Pathogens are limited to a small area of the body  boils  abscesses Systemic infection Infection throughout the body  measles Focal infection Systemic infection that began as a local infection  can arise from areas such as teeth, tonsils, or sinuses Sepsis Toxic inflammatory condition arising from the spread of microbes, especially bacteria or their toxins, from a focus of infection Bacteremia Bacteria in blood Septicemia Growth of bacteria in blood  ex. of sepsis: blood poisoning Toxemia Toxins in the blood  tetanus Viremia Viruses in blood Primary infection Acute infection that causes the initial illness Secondary infection Opportunistic infection after a primary (predisposing) infection Subclinical disease No noticeable signs or symptoms (inapparent infection)  poliovirus  hepatitis A Predisposing Factors (makes the body more susceptible to disease)  short urethra in females  inherited traits, such as the sickle cell gene  climate and weather  fatigue  age  lifestyle  chemotherapy Stage of disease Reservoirs of Infection  Continual sources of infection o Human: AIDS, gonorrhea  Carriers may have inapparent infections or latent diseases o Animal: rabies, Lyme disease  Zoonoses: a disease that is transmitted to humans from other animals o Nonliving environment: botulism, tetanus  Soil Transmission of Disease (Contact) Direct Requires close association between infected and susceptible host Indirect Spread by fomites (objects or materials that are likely to carry infection, such as clothes, utensils, and furniture)…nonliving Droplet Transmission via airborne droplets Vehicle transmission  Transmission by an inanimate reservoir o Food o Water o Air Vectors  Arthropods, especially fleas, ticks, and mosquitoes  Transmit disease by 2 general methods o Mechanical transmission  Arthropod carries pathogen on feet o Biological transmission  Pathogen reproduces in vector Nosocomial infections  Are acquired as a result of a hospital stay  Affect 5-15% of all hospital patients C. difficile  Anaerobic, endospore-former  Normally in large intestine  Survive many antibiotics, rapidly proliferate  Disease symptoms range from diarrhea to life-threatening colitis  Easily spread (hands, sheets, etc.)  Scrub hands with soap and water to remove spores  Sporocidal disinfectants to clean rooms  Use aseptic techniques Emerging Infectious Diseases  New  Increasing in incidence  Showing potential to increase in near future  75% are zoonotic (mostly viral and vector-borne)  Contributing factors o Genetic recombination between organisms  E. coli O157, avian influenza (H5N1) o Evolution of new strains  V. cholera )139 o Inappropriate use of antibiotics and pesticides  Antibiotic-resistant strains o Changes in weather patterns  Hantavirus (rodents) o Modern transportation o Ecological disaster, war, and expanding human settlement o Animal control measures o Public health failure Epidemiology  Study of where and when diseases occur  CDC (centers for disease control and prevention) o Collects and analyzes epidemiological information in US  Scientists o John Snow (1848-1849)  Descriptive o Ignaz Semmelweis (1846-1848)  Experimental o Florence Nightingale (1858)  Analytical Descriptive Collection and analysis of data Experimental Controlled experiments Analytical Comparison of a diseased group and a healthy group Case reporting Health care workers report specified disease to local, state, and national offices Nationally notifiable diseases Physicians are required to report occurence Morbidity Incidence of a specific notifiable disease Mortality Deaths from notifiable diseases Morbidity rate Number of people affected in relation to the total population in a given time period Mortality rate Number of deaths from a disease in relation to the population in a given time Ch 15 Microbial Mechanisms of Pathogenicity Pathogenicity The ability to cause disease Virulence The extent of pathogenicity For a pathogen to cause disease it must  Have access to host  Adhere to host  Colonize host  Damage host Portal of Entry  Mucous membranes membranes (respiratory tract, urogenital tract, etc.)  Skin including hair follicles and sweat glands  Parenteral route deposited under skin (cuts, bites, etc.)  Pathogens have preferred portal of entry Numbers of Invading Microbes ID Infectious dose for 50% of the test 50 population (virulence of microbe) LD 50 Lethal dose of a toxin for 50% of test population (potency of toxin) Ex: Bacillus anthracis Portal of entry ID50 Skin 10-50 endospores Inhalation 10,000-20,000 endospores Ingestion 250,000-1,000,000 endospores Ex: Toxins Toxin LD 50 Botulinum 0.03 ng/kg Shiga toxin 250 ng/kg Staphylococcal enterotoxin 1350 ng/kg Adherence  Adhesins/ligands bind to receptors on host cells  Biofilms form  M proteins o Part of fimbrae o Gives resistance to phagocytosis and aids in adherence Cell Wall Components  M protein resists phagocytosis (Streptococcus pyogenes)  Opa protein inhibits T helper cells (Neisseria gonorrhoeae)  Mycolic acid waxy lipid, resists digestion (Mycobacterium tuberculosis) Enzymes Coagulase Coagulates fibrinogen in blood (clot) Kinases Digest fibrin clots Collagenase Hydrolyzes collagen spread of gas gangrene IgA proteases Destroy IgA antibodies (defense against adherence of pathogens to mucosal surfaces Penetration into the Host Cell Cytoskeleton  Invasins o Salmonella alters host’s actin to enter a host cell  Use actin to move from 1 cell to the next  Listeria can propel from 1 host cell to another Direct Damage of Host Cell by Bacterial Pathogens  Disrupt host cell functions  Use the host cell for nutrients  Produce waste products  Viruses can multiply and rupture the host cell Production of Toxins (causes most damage) Toxin Substance that contributes to pathogenicity Toxigenicity Ability to produce a toxin Toxemia Presence of toxin in the host’s blood Toxoid Inactivated toxin used in a vaccine Antitoxin Antibodies against a specific toxin Mechanisms of Exo- and Endotoxins  Exotoxins o Are proteins produced inside pathogenic bacteria o Most commonly gram-positive bacteria, as part of their growth and metabolism o Secreted into surrounding medium during log phase o Specific for a structure or function in host cell o Disease specific o Are among the most lethal substances known o Soluble in body fluids  Can diffuse into blood and are rapidly transported throughout the body o Nomenclature  Classification based on mechanism of action  Superantigens: provoke intense immune response (bacterial proteins) o Cause intense immune response due to release of cytokines from host cells  Cytokines: small protein molecules produced by various body cells that regulate immune responses and mediate cell-to-cell communication  Membrane-disrupting toxins: escape tunnels for bacteria, can cause lysis of the host cells o Lyse by  Making protein channels in the plasma membrane  Leukocidins: lyse WBC’s  Hemolysins: lyse RBC’s  Disrupting phospholipid bilayer  A-B toxins: consist of 2 parts o A and B polypeptides: most exotoxins are A-B toxins  Part A: active enzyme component  Part B: host cell binding component o Actions 1. Bacterium produces and releases exotoxin 2. B (binding) component of exotoxin attaches to host cell receptor 3. A-B exotoxin enters host cell by receptor-mediated endocytosis 4. A-B exotoxin enclosed in pinched-off portion of plasma membrane during pinocytosis 5. A-B components of exotoxin separate a. A component alters cell function by inhibiting protein synthesis b. B component is released from host cell Important about Exotoxin Source Mostly gram positive Relation to microbe By-product of growing cell Chemistry Protein Fever? No LD 50 small  Endotoxins o Are lipid portions of lipopolysaccharides (LPS) of outer membrane of cell wall o Of gram-negative bacteria o Liberated when bacteria die and cell wall breaks apart o Lipid A is the endotoxin o All produce same signs and symptoms  Vary in degree  Septic shock shock caused by any bacteria  Endotoxic shock sudden loss of blood pressure caused specifically by gram (-) bacteria Important about Endotoxins Source Gram negative Relation to microbe Outer membrane Chemistry Lipid A Fever? Yes LD 50 Considerably large LAL Assay: used to detect presence of endotoxins  Amebocyte lysis produces a clot  Endotoxin causes lysis Pathogenic Properties of Fungi (do not have well defined set of virulence factors)  Waste products may cause symptoms  Chronic infections provoke an allergic response  Trichothecene toxins inhibit protein synthesis  Proteases allow attachment of fungi by changing host’s membrane  Capsule prevents phagocytosis  Examples o Ergot toxin: cause hallucinations (LSD) o Aflatoxin: carcinogenic properties (peanut butter) o Mycotoxins: very potent neurotoxin (mushrooms) Pathogenic Properties of Protozoa  Waste products may cause symptoms  Avoid host defenses by o Growing in phagocytes o Antigenic variation Pathogenic Properties of Helminths  Use host tissue for their own growth  Presence of parasite interferes with host function  Parasite’s metabolic waste can cause symptoms  Blocks lymphatic system leads to swelling of legs and other body parts Pathogenic Properties of Algae  Paralytic shellfish poisoning: similar to botulim o Saxitoxin Portals of Exit  Respiratory tract o Cough and sneeze  Gastrointestinal tract o Feces and saliva  Genitourinary tract o Urine and vaginal secretions  Skin  Blood o Arthropods that bite, needles or syringes Overall summary


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