Medical Microbiology Flashcards
What is the human microbiome?
The collection of all the microorganisms living in association with the human body (microflora, microbiota)
What is the number of human cells compared to the number of microorganisms in the body?
- 10^13 human cells
- 10^14 microorganisms
What is the number of genes in the human genome compared to the number of genes in the microbiome?
- 20,000 genes in human genome
- 20,000,000 genes in microbiome
When does colonization of microorganisms begin?
Right after birth
Where does the microbiota live?
Every exposed area of the body (skin, mucous)
Which parts of the body should be free of microbes?
Internal tissues (blood, muscles, organs)
What do the majority of microorganisms living inside the body do?
Harmless commensals that produce beneficial products & inhibit growth of pathogens
Which organism protects the female reproductive tract?
Lactobacillus acidophilus
What are the 3 different microenvironments of skin?
- Dry
- Moist
- Subcutaneous
What does higher moisture and warmer temperature skin allow for?
More microbes to grow
What are the 2 most common types of bacteria found on dry skin?
Betaproteobacteria & corynebacteria
What does corynebacterium diphtheriae cause?
Cutaneous diphtheria
What are the 2 most common types of bacteria found on moist skin?
Corynebacteria & staphylococci
What is an example of a harmless commensal found on skin?
Staphylococcus epidermis
What is an example of a pathogen found on skin and what does it cause?
- Staphylococcus aureus
- Causes boils, abscesses, & wound infections
What are examples of subcutaneous skin?
Oily skin around the nose and on the upper chest and back
What is the most common type of bacteria found on subcutaneous skin?
Propionibacteria
What are propionibacteria?
Anaerobic actinobacteria that produce propionic acid as an end-product of fermentation
What is an example of a bacteria found on subcutaneous skin and what does it do?
- Propionibacterium acnes
- Lives in hair follicles, eats sebum, which causes overgrowth and triggers inflammation/inflammatory acne
What are 2 antimicrobial enzymes found in saliva?
- Lysozyme
- Lacteroperoxidase
What is an example of an aerobic organism found in the mouth and where does it live?
Neisseria mucosa, which lives on mucous membranes like the tongue
What is an example of an anaerobic organism that lives in the mouth and what does it do?
- Streptococcus mutans, which is an aerotolerant anaerobe
- Produce a sticky dextran slime layer that lets it stick to surfaces
- Produces lactic acid as a fermentation end-product
- Degrades tooth enamel
- Can lead to gingivitis
What causes the stomach to be inhospitable to most microbes?
Low pH & proteolytic enzymes
What is an example of a microorganism found in the stomach and what does it do?
- Helicobacter pylori
- Colonizes surface of membrane, protected from stomach acid by mucous
- Produces endotoxins to trigger inflammation & exotoxins to kill cells in the membrane
- Cause of stomach ulcers
What type of antibiotics treat stomach ulcers?
Tetracycline
Which part of the small intestine has the most bacteria?
The part with the most neutral pH
What is an example of an organism found in the small intestine and what are its characterisitcs?
- Enterococcus
- Gram positive lactic acid bacteria
- Opportunistic pathogen
- Can develop antibiotic resistance easily
What microorganism causes nosocomial infections of the small intestine?
Enterococcus
Why does the large intestine have an extremely large number of microbes?
pH is neutral and environment is anoxic
What type of microbes are commonly found in the large intestine?
Anaerobes and facultative aerobes
What is an example of a bacteria found in the large intestine and what are its characteristics?
- E. coli
- Indicator of fecal contamination
What are the largest group of bacteria found in the GI tract?
Strict anaerobes from Bacteroides & Clostridium
A high number of this kind of microbe may contribute to obesity and why?
Methanogens because they use up a lot of H2 which promotes bacterial fermentation, which makes nutrients available to the host
What was found in germ free mice compared to normal mice?
Germ free mice had 40% less body fat
What happened when germ free mice were inoculated with microbes compared to healthy mouse intestines?
Inoculated mice quickly gained weight
What was the difference in microbes between normal weight mice and genetically obese mice?
Genetically obese mice had fewer Bacteroidetes, more Firmicutes, and way more methanogens
What can changing the microbiota of the large intestine do to human health?
May cause opportunistic pathogens to take over
What happens in antibiotic associated colitis?
Clostridium difficile grows and the colon inflames
What can treat antibiotic associated colitis?
- Further antibiotics
- Probiotics
- Fecal transplant
What are the 3 most common bacteria found in the upper respiratory tract?
- Staphylococci
- Streptococci
- Carynebacteria
What mucosal tissue are usually free of microorganisms? (2)
- Lower respiratory tract
- Upper urinary tract
What kind of bacteria is found in the urethra?
Gram negative
What happens when some members of the normal microbiota are transferred to the urinary tract and what is an example of this?
- Can act as opportunistic pathogens
- E. coli causes urinary tract infections
What happens if the normal microbiota of the female reproductive tract is disturbed?
Yeasts can overgrow and cause yeast infections
What is an infection?
Growth of microbes that are not normally present in the host (does not necessarily mean host is harmed)
What is a disease?
Damage or injury that impairs regular host function
What is a pathogen?
Microbe that causes a disease
What is an opportunistic pathogen?
Microbe that causes disease only in the absence of normal host resistance
What are 2 examples of opportunistic pathogens and what do they cause?
- Streptococccus pneumoniae causes pneumonia in immunocompromised patients
- E. coli causes UTIs when bacteria from feces are moved into urethra
What is pathogenicity?
Ability to cause a disease
What is virulence?
Severity of the disease that is caused
What is an LD50 value?
Number of cells of a pathogen that will cause death in 50% of infected animals
What is an ID50 value?
Number of cells needed to infect animals (not kill)
If bacteria is in your body are you considered infected?
NO
What are 2 examples of LD50 values?
- Streptococcus pneumoniae LD50 = 50 cells
- Salmonella enterica LD50 = 5000 cells
What is pathogenesis?
The process by which a disease develops
What are virulence factors?
- Genetically encoded traits that contribute to a pathogen’s ability to cause disease
- The ability of a pathogen to stick to a surface and begin colonization
What are 2 examples of non-covalent virulence factors?
Slime layers & capsules
What are adhesins?
Specific surface molecules that allow selective adherence to a particular cell type
What does streptococcus mutans use a slime layer for?
To stick to teeth and form a biofilm
What does streptococcus pneumoniae use a capsule for?
- To stick to cells in lungs
- Protect cell from phagocytes
What do strains of enterotoxigenic E. coli use fimbriae for?
Adhere specifically to cells in the small intestine
What does neisseria gonorrhoeae use fimbriae for?
- Allow it to attach to mucosal epithelial cells
- Retract to bring bacteria close to membrane
What is invasiveness?
Ability of a pathogen to enter into host cells or spread through tissues
What are siderophores?
Iron binding molecules
What host proteins can sequester iron and make it unavailable for the microorganism?
Transferrin & lactoferrin
What do siderophores do?
Rip iron out of tissues to be used by bacteria
What are exoenzymes?
Excreted by bacteria to degrade host tissues
What does hyaluronidase do and what does this cause?
- Hydrolyzes hyaluronic acid which holds animal cells together
- Allows pathogen to spread between cells
What does collagenase do and what does this cause?
- Degrades collagen, which is a structural component of connective tissue
- Allows pathogen to spread through tissues
What do proteases, nucleases, & lipases do?
Degrade host macromolecules
What does fibrinolysin do?
Dissolves fibrin clots
Which microorganism makes streptokinase?
Streptococcus pyogenes
What does coagulase do?
Induces fibrin clots
Which microorganism produces coagulase and why?
Staphylococcus aureus to protect it from phagocytes
What are invasins?
Proteins that allow bacteria to invade and directly enter into host cells
What is an example of a microorganism that produces invasins and why does it produce them?
Listeria monocytogenes to promote phagocytosis by macrophages, allowing it to spread from cell to cell
What are characteristics of Listeria monocytogenes?
- Non-lactic acid
- Non-spore forming
- Psychrotolerant
- Member of Firmicutes
Where can Listeria monocytogenes be found?
In unpasteurized dairy products & improperly packaged processed meats
What does bacteremia mean?
Bacteria in the blood
What does septicemia mean and what can it lead to?
- Bacteria multiplying in the blood
- Can lead to sepsis (widespread systemic inflammation)
What type of bacteria generally causes septic shock?
Gram negatives, but sometimes by Gram positives
What do proteins that are released by growing bacteria do?
Inhibit host cell function (or kill host cells)
What are some virulence factors found in Bacillus anthracis?
Capsule, exoenzymes, and anthrax toxin
What are 3 categories of exotoxins?
1) Cytotoxins
2) AB toxins
3) Superantigens
What do cytotoxins do?
Disrupt cytoplasmic membrane integrity
What are 3 types of cytotoxins?
1) Hemolysins
2) Lecithinase/phospholipase
3) Leukocidins
What do hemolysins do?
Lyse many cells (not just RBCs)
What is an example of a hemolysin and what does it do?
- Streptococcus pyogenes
- Produces streptolysin that attacks sterols in the cell membrane
What does lecithinase/phospholipsase do?
Dissolve membrane lipids
What is an example of a lecithinase/phospholipase?
Clostridium perfringens, which is an alpha-toxin
What do leukocidins do?
Destory WBCs
What is an example of a leukocidin and what does it do?
- Staphylococcus auerus which is a staphylococcal alpha-toxin
- Toxin subunits insert into the membrane and oligomerize to form a heptamer, forming a pore that causes cell contents to leak out and kill the cell
What type of subunits are found in AB toxins?
Active subunit and Binding subunit (hence AB)
What is an example of an AB toxin and what does each of its binding sites do?
- Corynebacterium diphtheriae
- Subunit B specifically binds to a protein on animal cells
- Subunit A then moves across the membrane
What do superantigens do?
Activate T cells to elicit an extreme immune response
How do superantigens work?
- Bind to MHC molecules and TCRs outside the antigen binding sites
- Bridge the gap and mimics proper antigen presentation
What are symptoms of superantigens?
Extreme fever, systemic inflammation, shock, death
What is an example of a superantigen?
Staphylococcus aureus’ toxic shock syndrome toxin
What is a general example of an endotoxin?
- Lipid A on lipopolysaccharides from Gram negative outer membrane
- Released when cells die
Are endotoxins or exotoxins considered more toxic?
Exotoxins
What are 2 specific examples of endotoxins and what do they do?
- Salmonellosis – salmonella colonizes intestine; as they die they release endotoxins that cause fever, diarrhea, and generalized inflammation
- Gram negative sepsis – gram negative bacteria multiply in the blood; when killed by immune system they release endotoxins which leads to massive inflammation causing septic shock and death
