Normal flora Flashcards
Overview of normal oral flora
aka “normal throat flora”
Aerobes: Viridans streptococci Neisseria (NOT meningitidis) Diptheroids Staphylococcus epidermidis Facultative: Eikenella
Lots of anaerobes - show up on Gram, not culture
Overview of normal flora
Non-pathogens vs “carrier state” = colonization with pathogen
Specific to anatomic sites
- ex ratio anaerobes: aerobes 1:1 in most sites (higher in colon, gingiva, nose, vagina, endocervix)
Beneficial
- prevent colonization with pathogens
- nutrition - produce B12, vitamin K
Bad
- can cause disease in immuno-compromised
- can cause disease if imbalanced (ie some suppressed -> C diff)
* - low motility, obstruction -> overgrowth -> fat malabsorption, B12 deficiency*
Oral aerobes
Viridans streptococci - Gram (+) chains
- large numbers 10>6/mL
- highly adherent -> plaque -> heart valve myocarditis
- love sugar -> ferment to lactic acid
- alpha hemolytic on blood agar
Neisseria - Gram (-) diplococci
- non-pathogens vs meningitidis (can rarely colonize)
Diptheroids - Gram + rods, pleiomorphic
- Corynebacteria but not C diptheriae
- also skin -> most common blood culture contaminant
- can cause disease on devices
Staphylococcus epidermidis - Gram +, coagulase (-)
- also skin -> blood culture contaminant
- can cause disease on devices
Oral aerobic colonization
Normal throat flora - not usually listed on results
Antibiotics -> colonization with resistant/pathogenic
- Gram (-) rods, Staph aureus, yeasts
Colonization with potential pathogens - 5-40% prevalence
- Pneumococcus, Staph aureus
Hospitalization + antibiotics -> aerobic Gram (-) rods
- E coli, Klebsiella
Eikenella corrodens - facultative aerobe, Gram (-) rod
- infects bites, fists
Oral anaerobes
Large numbers on mucous membranes
- Gram stain but normally don’t culture
- usually penicillin sensitive!
- often very O2 sensitive
Fusobacterium - thin Gram (-) rod
Prevotella melaninogenicus - Gram (-) rod
Bacteroides corrodens - Gram (-) rod
Peptostreptococcus - anaerobic Strep (Gram +)
Actinomyces - Gram + filamentous, branching
Porphyromonas gingivalis -> plaques
Spirochetes
Disease from oral flora
Periodontal
Aspiration pneumonia -> mixed aerobe and anaerobic
- oral flora should not extend into trachea!
Penicillin sensitive
Many organisms -> don’t always identify
Stomach flora
Normally sterile due to pH
Can colonize in gastric achlorhydria (no HCl) or obstruction
Upper small intestine flora
Generally sterile due to peristalsis, bile acids
- small (< 10>5/mL) from oral and upper respiratory
- Gram + aerobes, few anaerobes
Stasis (ex gastric bypass surgery) -> increased flora
Ileum flora
Resemble colon/fecal but smaller numbers (10>6/mL)
- can have stasis -> increase
Coliforms - E coli, Klebsiella, other Gram (-)
Anaerobe = Bacteroides fragilis - most dominant
- penicillin resistant!
- use clindamycin, cefoxitine, metronidazole
Colonic/fecal flora
Large numbers (10>10-12/mL) due to higher pH, stasis Mostly anaerobes (Bacteroides)
Bacteroides fragilis - Gram (-) rod
Bifidobacterium - Gram + rod
Lactobacilli - Gram + rod
Clostridium (ex perfringens) - up to 1/3 of cultures (10>6/g)
Aerobes:
- coliforms (Gram (-) rods), Enterococcus
- infrequent S aureus, Pseudomonas, Proteus, Klebsiella
Anaerobes:
- >=400 species in low numbers
-> gas = methane, H2
Bacteroides fragilis
Most predominant colonic/fecal (10>10-11 CFU/g)
Gram (-), anaerobic, non-spore, pleiomorphic rods
Metabolism -> ammonia (from urea, proteins), acid, gas
Frequent cause of mixed intra-abdominal (ex rupture)
- resistant to penicillin -> clindamycin, cefoxitin, metronidazole
- mixed with anaerobic Gram (-)
-> smelly, gassy, necrotic infection
-> aminoglycoside (gentamycin)
Grows in routine anaerobic cultures
Bifidobacterium
Gram + rod, non-spore
Found in 2/3 of fecal samples
- 10>9 CFU/g
Non-pathogenic
Sensitive to penicillin
Lactobacilli
Gram + rod
Produce lactic acid -> low pH -> prevent pathogens
ex yogurt, vagina
Dev’t of colonic flora
Sterile at birth - colonized in hours
Breastfeeding -> Bifidobacterium
Weaning or bottle -> colonized similar to adult
Maintenance - depends on conditions
synergy:
- aerobes maintain re-ox potential (low O2)
- produce growth factors (ex Vitamin K) -> others use
antagonism
- pH - partially from fermentation
- some organic acids specifically prevent other growth
- bacteriocins released
Antibiotics disrupt normal flora -> Salmonella, Shigella, C difficile
May have distinct subtypes:
- Enterotype 1 -> Bacteroides predominant -> B7
- Enterotype 2 -> Prevotella predominant -> B1
- Enterotype 3 -> Ruminococcus
Colonic flora metabolism
Bile acids deconjugation
- conjugated acids necessary for fat absorption
-> flora converts to free bile acid
-> small intestine overgrowth -> fat malabsorption
Ammonia: bacterial metabolism (protein) -> blood levels
- sterile animal -> decreased ammonia levels
- hepatic coma -> tx with antibiotics, enemas to reduce flora
Bile pigments: bilirubin -> urobilin -> stercobilin
Carbs: non-digested -> fermentation -> pH
Intermediates (ex TMAO) -> heart disease risk
Correlation with weight: obese (Bacteroidetes) vs thin (firmicutes)
