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28 Cards in this Set
- Front
- Back
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Most microorganisms are benign |
Few contribute to health and fewer pose direct threats to health |
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Normal microbial flora |
Microorganisms usually found associated with human body tissue -Humans are colonized by microorganisms before birth & at birth |
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Describe the normal microflora of the skin. |
-The skin is generally a dry, acidic environment that does not support the growth of most microorganisms -Moist areas (e.g. sweat glands) are readily colonized by gram-positive bacteria and other normal flora of the skin |
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The skin microflora composition is influenced by what? |
-Environmental factors (e.g. weather) -Host factors (e.g. age, personal hygiene) |
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What are the three general environments on the skin? |
Sebaceous skin, moist skin, & dry skin |
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The oral cavity is a complex, heterogenous microbial habitat. Bacteria colonize tooth surfaces by first attaching to acidic glycoproteins deposited there by saliva |
Saliva contains antimicrobial enzymes -But high concentrations of nutrients near surfaces in the mouth promote localized microbial growth The tooth consists of a mineral matrix (enamel) surrounding living tissue (dentin & pulp) |
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Extensive growth of oral microorganisms, especially streptococci, results in a thick bacterial layer (dental plaque) |
As plaque continues to develop, anaerobic bacterial species begin to grow |
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The human GI tract: |
-Consists of the stomach, small intestine, and large intestine -Responsible for digestion of food, absorption of nutrients, & production of nutrients by the indigenous microbial flora -Contains 10^13 to 10^14 microbial cells |
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Microbial populations in different areas of the GI tract are influenced by what? |
Diet and the physical conditions in the area |
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What prevents many organisms from colonizing the GI tract? |
The aciditiy of the stomach & the duodenum of the small intestine (~pH 2) |
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Intestinal microorganisms carry out a variety of essential metabolic reactions that produce various compounds. The type & amount produced is influenced by the composition of the intestinal flora & the diet. The compounds produced include: |
-Vitamins -Gas, organic acids, & odor -Enzymes |
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Details of the human gut microbiome |
-Active area of research -Obesity, diabetes, asthma, dermatitis, IBD all appear to be influenced by gut microbiota |
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Describe normal microflora in the respiratory tract. |
-A restricted group of organisms colonizes the upper respiratory tract (Ex. Staphylococci, streptococci, diphtheroid, bacilli, & gram-negative cocci -The lower respiratory tract lacks microflora in healthy individuals |
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Describe normal microflora in the urogenital tract. |
-The bladder is typically sterile in both males & females -Altered conditions (such as pH change) can cause potential pathogens in the urethra (such as E. coli & Proteus mirabilis) to multiply & become pathogenic -E. coli & P. mirabilis frequently cause UTIs in women |
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Virulence |
The relative ability of a pathogen to cause disease |
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Describe methods in measuring virulence. |
-Virulence can be estimated from experimental studies of LD50 -The amount of an agent that kills 50% of the animals in a test group -Highly virulent pathogens show little difference in the number of cells required to kill 100% of the population as compared to 50% of the population |
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Attenuation |
The decrease or loss of virulence |
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Toxicity |
Organism causes disease by means of a toxin that inhibits host cell function or kills host cells -Toxins can travel to sites within host not inhabited by pathogen |
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Invasiveness |
The ability of a pathogen to grow in host tissue at densities that inhibit host function -Can cause damage without producing a toxin -Many pathogens use a combination of toxins, invasiveness, and other virulence factors to enhance pathogenicity |
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Describe initial pathogen invasion |
-Starts at the site of adherence -May spread throughout the host via the circulatory or lymphatic systems |
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Describe specific adherence. |
-A pathogen must usually gain access to host tissues and multiply before damage can be done -Bacteria and viruses that initiate infection often adhere specifically to epithelial cells through macromolecular interactions on the surface of the pathogen and the host cell |
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Bacterial adherence can be facilitated by what? |
Extracellular macromolecules that are not covalently attached to the bacterial cell surface -Ex. slime layer, capsule -Fimbriae & pili |
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Describe colonization and infection. |
-The availability of nutrients is most important in affecting pathogen growth -Pathogens may grow locally at the site of invasion or may spread throughout the body |
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Pathogens produce enzymes that do what? |
Enhance virulence by breaking down or altering host tissue to provide access to nutrients -Ex. hyaluonidase Protect the pathogen by interfering with normal host defense mechanisms -Ex. coagulase |
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Exotoxins |
-Proteins released from the pathogen cell as it grows -Three categories: cytolytic toxins, AB toxins, & superantigen toxins (huge immune response) |
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Cytolytic toxins |
Work by degrading cytoplasmic membrane integrity, causing cell lysis & death -Toxins that lyse red blood cells are called hemolysins -Staphylococcal alpha-toxin kills nucleated cells & lyses erythrocytes |
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AB toxins |
-Consist of 2 subunits; A & B -Work by binding to host cell receptor (B subunit) & transferring damaging agent (A subunit) across the cell membrane -Examples: Diphtheria toxin, tetanus toxin, botulinum toxin |
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More on exotoxins |
-Clostridium tetani & Clostridium botulinum produce potent AB exotoxins that affect nervous tissue -Botulinum toxin consists of several related AB toxins that are the most potent biological toxins known |
