MicroBio chapter 23 guided reading for exam 3
MicroBio chapter 23 guided reading for exam 3 BIOS 350
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This 9 page Study Guide was uploaded by Yara Albair on Friday October 7, 2016. The Study Guide belongs to BIOS 350 at University of Illinois at Chicago taught by Professor Gibbons in Fall 2016. Since its upload, it has received 8 views. For similar materials see General Microbiology in Biology at University of Illinois at Chicago.
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Date Created: 10/07/16
Guided Reading Chapter 23 1. Compare and contrast the characteristics of our mucous membrane and our skin. Explain which one is a more hospitable place for microorganisms to grow and explain why. Name the three major skin microenvironments and describe what adaptations the microbes that live there must have. The mucous membrane is a colonization site consisting of epithelial cells that interface with the external environment. This membrane found in many locations in the body, such as the urogenital, respiratory, and gastrointestinal tracts. The epithelial cells secrete mucous in the mucous membranes containing water soluble proteins and glycoproteins. This mucous prevents microbes from attaching and these microbes are swept away by sneezing. The skin is a complex organ that consists of several distinct microenvironments containing microflora. A distinct microenvironment includes the moist skin area inside the nostril, armpit, or umbilicus. This moist skin is briefly separated dry microenvironments such as the forearms and palms. A third microenvironment has areas with high sebaceous gland concentrations. Those glands produce sebum, oily substances found on the back of the scalp, side of the nose, and upper chest and back. Each of these three microenvironments contain unique microbes, for example, moist sites contain staphylococci, and drier sites have more mixed populations such as corynbacteria and others. Environment and host are factors that influence the composition of the normal skin microflora. For example, and increase in weather temperature or moist may cause an increase in the density of skin microflora. Another effect could also be the age of the host as young children carry more pathogenic gram negative bacteria and have a variety of microflora. Personal hygiene is an important factor and poor hygiene increases the risk of having microbes on the skin. Low moisture and acidic pH prevent the growth of microorganisms on the skin. 2. Explain why the diversity of microbes in the oral cavity changes after the first year of life. Explain how changes in oxygen amount and changes in pH can influence the microbiome of the gastrointestinal tract. Explain why the lowering of GI microbes while taking antibiotics can lead to adverse health problems. Even though saliva contains microbial nutrients, it is not considered a good growth medium because these nutrients are present in low concentrations and saliva contains antibacterial substances. Lysozyme is an enzyme found in saliva and cleaves glyosidic linkages in peptidoglycan of the bacterial cell wall, causing lysis. Lacto peroxidase if found in both saliva and milk and it kills bacteria by oxygen generation reactions. However, these microbes get the nutrients needed for growth from food particles as well as cell debris near the teeth and gums. The tooth consists of calcium phosphate crystals surrounding the tissues. The bacteria found in the mouth in the first years of life are aero tolerant anaerobes and few of them are aerobes. After teeth start appearing, these newly created surfaces are now slowly starting to be colonized by anaerobes that are adapted to grow in biofilms on the teeth surface and in gingival crevices. The fluids in the stomach have a high acidity of 2 making it a chemical barrier, preventing microbes from entering the GI tract. However, these microbes do have the ability to populate this environment because they have several bacteria taxa and most of these microbes enter the stomach through organisms found in the oral cavity and enter with food. The small intestine has two different environments in the duodenum which is fairly acidic and its microflora are similar to that of the stomach. As we travel to the ileum, the pH becomes less acidic and there is an increase number in bacteria. The large intestine consists mostly of the colon where prokaryotes are mostly present and is considered a place for in vivo fermentation. Facultative aerobes are present in smaller numbers and they consume the remaining oxygen making the large intestine anoxic, thus promoting growth of obligate anaerobes such as many species of Bacteroides. When antibiotics are taken orally, they inhibit normal floras from growing and target pathogens as well, leading to the loss of antibiotic susceptible bacteria in the intestines. In the absence of normal flora, opportunistic pathogens affect the digestive system and cause disease. Antibiotic treatment allows certain bacteria such as c. difficult to grow without competition from the normal flora, causing infections. When the antibiotic therapy ends, normal intestinal flora begins to reestablish again in adults and we can speed this process by the use or probiotics. Rapid recolonization may reestablish a competitive local flora that outcompete pathogens. 3. Explain why only the upper respiratory tract is colonized with microbes in healthy individuals. Explain why potential pathogens found in the normal flora of the upper respiratory tract do not typically cause disease. Note the typical pH of the vagina in adult women and explain why this is the case. Explain why women of childbearing age often develop a vaginal yeast infection when they are on antibiotics. How can their diet help alleviate the problem? Note why women are more prone to urinary tract infections. Microorganisms live in the upper respiratory tract along with secretions of the mucous membrane. These bacteria enter the upper tract from air during breathing or are trapped in the mucous of the nasal and oral passages. Some microbes colonize the respiratory mucosal surfaces in all individuals. Some pathogens such as staphylococcus are part of the normal flora in healthy nasopharynx. These healthy individuals are carriers of the pathogens but do not necessarily develop the disease due to high competition with other microbes for food sources and nutrients. Innate immune system as well as some components of the adaptive system work to prevent pathogens from growing. Female vaginas have a pH lower than 5 and contain high amounts of glycogen. Lactobacillus acidophilus is an organism that ferments the polysaccharide glycogen and produces lactic acid thus maintaining a local acidic environment. Yeast, streptococci another organism are also found. Before puberty, L. acidophilus is not yet present making the vagina neutral and not able to produce glycogen. After menopause, glycogen production stops, causing the pH to rise and the flora is similar to what it was before puberty. E. coli and Proteus mirabilis are found in small numbers in the body. they can multiply when conditions allow them to, such as a change in pH, causing frequent infections in the urinary tract, especially in females. Women taking antibiotics at childbearing age can lower the amount of lactobacillus that helps keep the pH of the vagina acidic, thus yeast increases in growth leading to yeast infection. They can prevent this by avoiding yeast fermented food such as alcohol as well as eliminating simple sugars. Guided Reading Chapter 23 1. Define the following terms with an example: a. Infection: Growth of microbes that are not normally present within the host such as tuberculosis. b. Host: The organism that provides support to the virus to help it grow and survive. Such as a bacterial cell acting as a host cell for the DNA isolated from a bacteriophage. c. Pathogen: A microorganism that causes disease. Such as a Virus or a Bacteria. d. Disease: When pathogens or other microbes affect the function of the host and cause damage or injury to it. such as cold. e. Pathogenicity: The ability of the pathogen to cause disease. such as the ability of a cold virus to cause cold. f. opportunistic pathogen: An organism that causes disease when the host has no resistance. Example: Candida albicans that cause infections in the genitals. g. Virulence: Measure or ability of a pathogen to cause disease. A flagella is a virulent since it helps the pathogen move, enter the cell and cause disease. h. Attenuation: Decrease of virulence of a pathogen. such as influenza vaccine. 2. Observe figure 23.10 in your textbook. Explain why the Salmonella microbes is considered only moderately virulent with a LD 50higher than the Streptococcus microbe with the lower LD . 50 In a study on experimental infections mice, it was shown that highly virulent pathogens show little difference in cell numbers required to kill 100% of the text group compared with the requirement to kill 50% using LD50. LD50 is not proportional to the number of cells delivered wince only few strains of streptococcus are required to kill all mice. On the other hand, Salmonella, which is less virulent, required less cells to kill all mice and is about 10,000 fold greater than the highly virulent Streptococcus and LD50 is proportionally related to the number of pathogen cells introduced into the test mice. 3. Construct a Venn diagram comparing and contrasting the various adherence structures bacteria have. Explain why adherence structures are considered virulence factors. Using tooth decay as an example explain how infection can lead to disease under the right environmental conditions. Adherence is the ability of a microbe to attach to the cell surface. Glycocalyx are surface molecules composed of polysaccharide components located outside the bacterial cell wall. They are a loose network of polymer fibers that extend outward. For example, it exists in Bacillus a. as a capsule and forms smooth slimy colonies. Slime layers are network of polymers surrounding the cell and are important for adherence to other bacteria as to host tissues. Capsules play a role in protecting pathogenic bacteria from host defense mechanisms. Other adherences include fimbriae and pili, which are proteins found on the surface of the cell and help in the attachment process. They work by binding host cell surface glycoproteins to initiate adhere. Flagella work to increase adherence to host cells. All these factors make adherences a virulence factor since they can chieve colonization, immune evasion and suppression, and entry of the cell. Acidic glycoproteins from saliva can from a thin organic film even on clean tooth surfaces which provides an attachment site for bacteria. Over time, these bacterial growths cause a thick oral biofilm called plaque that continues to form bacteria. These bacteria extend to the tooth surface and makes a thicker biofilm. As this dental plaque continues to expand the microflora produces high concentrations of organic acids, especially lactic acid and that causes decalcification of the tooth that cause tooth decay. The ability of microorganisms to invade the calcified tooth enamel tissue plays a major role in the extent of dental caries, making them an infectious disease. 4. Differentiate between a localized and a systemic infection. Differentiate between bacteremia and septicemia. In each case explain which would be the more dangerous situation and why. Pick any ten virulence factors from table 23.5 of your text book and explain how they are beneficial for the microbe producing them and harmful to us leading to the disease state. Localized infections tend to stay in one area of the body while systemic spread from one area to the entire body. When pathogens remain localized after entering, they begin to multiply. When bacteria start to grow, organisms may cause bacteremia. Bacteremia is the presence of microorganisms in the blood. The spread of pathogens through the blood and lymph system causes blood borne systemic infection called septicemia that might lead to inflammation, septic shock, and death. Both bacteremia and septicemia start out as an infection in specific organs such as kidneys or lungs. Streptococci and staphylococci produce an enzyme called hyaluronidase that promotes spreading of organisms in tissues by breaking down the polysaccharide hyaluronic acid. This allows pathogens to spread from the initial infection this. Clostridia causes gas gangrene and produces collagenase that destroys collagen, enabling organisms to spread in the body. Streptococcus pyogenes produce a fibrinolytic substance called streptokinase that counter the process of clotting that isolates pathogens and limits infections. Staphylococcus aureus produce coagulase that causes insoluble fibrin to be deposited on s. aureus cells and protects them from being attacked by host cells. Corynebacterium produces AB toxins that serve as elongation factors in the cell that binds to ribosomes and allows amino acids to attach to it. B subunit allows diphtheria to bind to the cytoplasmic membrane making a cleavage of toxins that allows subunit A to enter the cell wall. Clostridium botulinum produce acetylcholine when peripheral and cranial nerves are stimulated which binds to specific receptors on the muscle. Botulinum prevents the release of acetylcholine resulting in lack of stimulus to muscle fibers. Clostridium tetani causes tetanus that binds to interneuron and prevents the release of glycine that induces muscle relaxation. This results in constant release of acetylcholine to muscle fibers and irreversible contract of muscle. Clostridium perfringens causes gas gangrene and food poisoning and lecithinase enzyme is produced that dissolves the cytoplasmic membrane of red blood cells. Corynebacterium diphtheriae produces AB toxin called diphtheria that binds to cytoplasmic membrane and causes proteins to elongate. Vibrio cholerae causes cholera, which is a heat stable toxin that disrupts normal ion flow in the intestine and causes dangerous diarrhea. 5. Construct a chart comparing and contrasting exotoxins and endotoxins properties with specific examples of each type. Explain whether or not bacterial growth and infection in the host is necessary for the production of toxins using examples to explain your logic. Explain why individuals with a Gram-positive infection need not worry about endotoxins. Property Exotoxins Endotoxins Chemical Made of Made of proteins, lipopolysacchar secreted by ide and gram positive lipoprotein and negative complexes, bacteria, released in destroyed by toxic amounts heat. when cell lyses, and is part of the outer membrane of gram negative bacteria, stable and heat tolerant. Action and Binds to cell Fever, diarrhea, symptoms receptors, and vomiting. could be cytotoxic, enterotoxin or neurotoxin, and performs specific action on tissues. Toxicity Highly toxic Moderately and sometimes toxic and rarely fatal. fatal. Immunogenicity Stimulates the Poorly response production of immunogenic. an antitoxin neutralizing antibody. Toxoid Destroyed by None potential heat or chemical treatments but traded toxoid remains immunogenic. Fever potential Doesn’t Produces fever produce fever in host. Genetic origin Encoded on Chromosomal extrachromoso genes. mal elements. Bacteria produces two types of toxins: Exotoxins which are released from bacterial cells and act at tissue sites removed from the site of bacterial growth. Endotoxins are cell-associated substances and are component of the outer membrane of gram negative bacteria. Second type is Endotoxins that may be released from growing bacterial cells and cells that are lysed as a result of effective host defense. and example of that is a lysozyme or the activities of certain antibiotics such as penicillins. Bacterial toxins, both soluble and cell associated, are transported and can cause cytotoxic effects at tissue sites remote from the local site invasion. People with gram positive infections do not need to worry about endotoxins because endotoxins are toxic lipopolysaccharides and are structural components of the outer membrane of gram negative bacteria. They are not soluble products of growing bacteria and are cell bound, released in toxic amounts when the cell lyses. 6. Explain factors that influence susceptibility to infectious disease in infants, adults, and the aged. Observe figure 23.25 of your textbook. Pick any five ways our natural host resistance mechanisms protect us from pathogens correlating it with pathogens and virulence factors they produce listed in table 23.5. For example, the mucus and cilia of our trachea help trap and sweep away Streptococcus pyogens from respiratory surfaces so that they can’t use their hyaluronidase to dissolve connective tissue and invade further tissues. Infectious diseases are common in very young and very old people. In infants, the intestinal microflora develops quickly, and before it develops, pathogens have the ability to access and produce disease. Infants for example can acquire diarrhea by E. coli. Adults over 65 years or age are more susceptible to respiratory infections caused by influenza because their ability to produce an immune response has declined. Anatomical changes also play a factor, such as the enlargement of the prostate gland in men over 50 causes a decrease in urinary flow, thus infecting the urinary tract. Stress also makes a healthy individual more susceptible to disease. Diet is a major key that affects host susceptibility to infection. Low protein and calories diet, for example, allow opportunistic pathogens to grow and multiply. Natural host resistance mechanisms include: The skin which is a barrier that produces antimicrobial fatty acids and antibacterial peptides such as E. coli, a microbe that causes Gastroenteritis. Tears contain lysozyme that dissolve cell walls of bacteria such as Shigella dysenteriae that inhibits protein synthesis, causing bloody diarrhea. Blood and lymph proteins inhibit microbial growth such Clostridium tetani that causes tetanus. In lungs, mucus, antibacterial peptides, and phagocytes prevent lung infections such as blocking Bordetella pertussis that causes whooping cough. The stomach has an acidity of pH 2 that prevents microbes such as Salmonella that causes typhoid and paratyphoid fevers.
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