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38 Cards in this Set
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Common features of Anaerobic Infections:
1) Origin 2) Characteristics 3) Predisposing conditions 4) Location 5) Redox potential 6) Species |
1) Many abscesses originate from native flora (anaerobes are a large part of native flora)
2) Foul-smelling discharge, gas, necrotic tissue 3) pulm aspiration, bowel surg, poor dental hygiene, bites, trauma, malignancy 4) Most in deep or necrotic tissues (low O2 and high access to endogenous bacteria) 5) Healthy tissues have high oxid-red potential due to presence of O2, can't support anaerobe growth. Oxidation-reduction potential may decrease due to - Wound, impaired blood supply, necrosis 6) All are "mixed" : >1 offending organism with 1 or more anaerobe or microaerophilic (fac anaerobe) organism Side note: most aerobic infections involve a single species |
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Predicting anaerobic species involved:
Knowledge of flora influences therapy b/c: |
1) by normal flora found in mucous membranes near infection site
2) Bacteroides fragilis is found in infections below the waist (penicillin resistant) - disting upper and lower GI Oral infections: penicillin sensitive, G+ cocci, mixed anaerobic infections Intraabdominal: penicillin resistant, G- rods, mixed anaerobic infections |
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How to ID clinically important Anaerobic Bact:
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Correct Specimen sampling and inject directly into culture tubes or bottles (v. little air exposure!)
Anticipate mixed infection (aerobic and anaerobic) Gram stain Morphology (colonies, spores) Unusual FA production (analyze with gas chromatography) Other Metabolic characteristics Don't submit oral or fecal cultures for anaerobes (have been subjected to air) Antibiotic sensitivity assays aren't as reliable as for aerobes |
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Common anaerobic media:
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Thioglycollate broth: chemical reducing agent, removes oxygen from liquid media
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Anaerobic G+ Rods:
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Bacteriodes fragilis
Prevotella (Bacteroides) melaninogenicus Fusobacterium |
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Non-Spore Forming Anaerobic G+ Rods:
Spore forming G+ rods: |
Bifidobacterium
Propionobacterium (diptheroid) Lactobacillus Actinomyces Clostridia |
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Anaerobic G+ cocci:
Anaerobic G- cocci: |
Peptostreptococcus
Veillonella |
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Bacteroides fragilis:
location resistance growth conditions septicemia common infections capsule E. coli treatment |
pleiomorphic, most common
anaerobic G- rod Large #s in small intestine Resistant to bile bactericidal activity, and *Penicillin resistant* In clinical specimens - DOESN'T require strict anaerobic conditions to survive During growth - may tolerate traces of O2, but definitely anaerobic causes septicemia via extraintest invasion, almost as common as Clostridia perfringens (these both cause ~80% anaerobic septicemias -> only 10% bacteremias caused by anaerobes -> these both cause 8% of all septicemias) common in intraabdominal (bowel rupture) and female genital infections - foul smell, gas production, necrotic Capsule = MAJOR virulence factor (only strains with capsule produce abscess in animal models) Infections in comb with E. coli are more severe Don't use penicillin (below the diaphragm), Use clindamycin, cefotoxin, metronidazole, aminoglycoside antibiotics (like gentamicin) |
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Prevotella (Bacteroides) melaninogenicus:
infection location disease caused Resistance/sensitivity Named for |
more common in oral infections, and occasionally in genital infect
serious cause of periodontal disease Many strains penicillin resistant, more sensitive to O2 than B fragilis Named for black pigment formed in colonies on blood agar plates and infected tissue = Hemin Hemin = precursor for cytochrome synthesis, required for growth |
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Fusobacterium:
morphology sensitivities infections caused |
tapered ends (needle shape), thin
sensitive to penicillin and oxygen (more than B. fragilis) oral and abdominalinfections, lung and liver abscesses, other pleuropulmonary infections, peritonitis |
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Propionibacterium (diptheroid):
morphology oxygen requirements location infection |
pleomorphic rod
aerotolerant (will grow in presence of low O2) normal skin inhabitant, often a contaminant in blood cultures doesn't usually cause infect rarely -> endocarditis in immunocompromised patients |
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Lactobacillus:
morphology location infections purpose |
NOT pleomorphic
Normally *lots* in intestine and vagina Used to make yogurt, sour milk, saurkraut NON PATHOGEN, but often associated with GU and GI tract Prevent growth of pathogens in vagina and intestine by maintaining low pH Converts Lactic acid to sugar |
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Actinomyces:
morphology oxygen requirements location infections |
G+ branching rods
Lesions contain microcolonies of actinomyces and cell debris with *Yellow sulfur granules* some strains aerotolerant oral pharynx and GI Usually mixed infections cervico-facial infections (oral or dental infections/abscesses), abdominal infections and sinus tract |
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Poststreptococcus:
morphology oxygen requirements location infections diagnosis |
G+ cocci, in chains
obligate anaerobe mouth, GU and GI tracts widely involved in infect, often in assoc with other anaerobes Found in pure culture or pleuro-pulmonary, OG-GYN infections, and brain abscesses |
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Veillonella:
morphology infections |
G- cocci
a commensual, not important pathogen |
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Anaerobic infection treatment:
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1) Penicillin - EXCEPT B. fragilis (*thus not used for infections below diaphragm*)
2)Newer Cephalosporins (cefoxitin) *more effective for B. fragilis* 3) Clindamycin 4) Chloramphenicol (bacteriostatic) 5)Metronidazole (trade name Flagyl) 6) For mixed aerobe-anaerobe: aminoglycosides plus antibiotic for anaerobes (ex - gentamycin and cefoxitin and clindamycin) 7) Surgically drain any abscesses (antibiotics can't kill bact in abscess) |
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Normal flora vs Carrier state:
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natural flora of body sites vs. carriage of pathogen in body sites
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Importance of normal flora:
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1) interfere with pathogen colonization
2) can cause disease if immunocompromised (ex suppression of part of normal flora with antibiotic) 3) Nutritional - ex intestinal bact produce vitB12 and K 4) *Overgrowth of sm intest bacteria can lead to obstruction or decreased motilit, fat malabsorption and vit B12 deficiency* 5) Each lesion has its own flora - knowing local flora will assist in choosing antibiotic when barrier is violated (wound) |
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Normal Mouth/Saliva Flora:
S. viridans |
aerobes or facultative Bact:
1) Streptococcus viridans: predominant mouth microorg (10^6/ml saliva) G+ cocci, may be in chains Most common cause of subacute bacterial endocarditis Highly adherent to dental tissue (plaque) and cardiac valves in bacteremia Thrive on sugar, some turn sucrose -> polysacch Dextran (component of plaque) with lactic acid byproduct |
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Neisseria:
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G- diplococci, coffee bean shape
second most predominant Non-path species as well as pathogenic (N. meningitidis which causes meningitis and can colonize in throat or nasopharynx) |
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Diptheroids:
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common name for non-pathogenic Corynebacterium species (except for C. diptheria which is pathogenic)
Pleomorphic, G+ rods most common contaminant in blood cultures along with S. epidermidis colonize the skin RARE infection cases reported in absence of foreign bodies |
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S. epidermidis:
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Major oral coagulase-negative staph species
G+ cocci, grape-like clusters most common blood culture contaminant along with diptheroids May be pathogens in the presence of foreign bodies (catheters, travasc artificial devices) |
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Eikenella corrodens:
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facultative, G- rod
part of normal oral flora causes skin and soft tissue infections assoc with human bites and clenched-fist injuries (bite wound on the hand, caused when a person's closed fist strikes the teeth of another person) |
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Role of Normal aerobic throat flora in disease:
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1) NTF eliminated by antibiotics may be replaced by more resistant G- rods or yeast -> drug resistant infections in pt's with malignancy or chemo
2) 5-40% of healthy individuals have low #s of potential pathogens in oral cavity (ex pneumococcus or staph aureus) 3) Hospitalization and antibiotics can allow G- rods to colonize (E. coli or Klebsiella |
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Oral Cavity Anaerobes:
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present in small #s in gums and throat
grow in close assoc with mucous membranes (gum/teeth interface) Common ones: 1)Fusobacterium (G- rod, cigar-shape) penicillin sens 2) Prevotella (G- rod), usually penicillin sens 3) Anaerobic streptococci (peptostreptococcus G+ cocci in chains, 15% bacteria in saliva) usually penicillin sensitive 4) Others (ex anaerobic spirochetes) |
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Lower Trachea:
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bacteria free in healthy individuals
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Diseases related to aerobes or anaerobes in the oral cavity:
treatment |
Aspiration pneumonia: caused by aspiration of own oral secretion, offending pathogens are mix of normal flora
may not be helpful to determine causative organism because many are involved many NFT aerobes and anaerobes sensitive to penicillin |
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Normal Stomach Flora:
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few organisms because of high acidity
Exceptions: in gastric achlorhydria (no stomach acid), Gastric obstruction (bact can proliferate) |
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Upper Sm Intestine Flora:
role of upper small intestine microflora in disease: |
Sterile in normal fasting subjects
If present, some G+ aerobes, few anaerobes, normally low #s and transported from mouth and resp tract Sterility due to rapid peristalsis and antibact properties of unconjugated bile acids Disease: Bacterial counts may increase in anatomical alterations cause stasis (ex post gastric bypass) |
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Normal flora of Terminal Ileum:
coliforms Anaerobes |
Stasis occurs here and allows for increase in bact #s
Usually 10^6/ml or less, species and #s closely resemble bact in feces Coliforms = E. coli, enterobacter, and other G- Anaerobes: ex B. fragilis, found mostly in lower intestine, not part of mouth flora, RESISTANT to penicillin |
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Normal flora of Large Intestine and Feces:
amount of bact |
marked bact proliferation b/c of stasis
bact is probably 1/3 - 1/4 weight of feces 10^10-10^12 bact per g wet feces |
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Normal flora of Large Intestine and Feces:
Species |
Bacteroides: G- anaerobic rods, non spore forming, pleomorphic
Metabolic generation of ammonia (*formed by splitting urea and proteins), acid, gas Bacteroides Fragilis: most common (see above) Others: Bifidobacterium: non spore forming, G+, penicillin sensitive, in 2/3 fecal samples, 10^9 bact/gm Lactobacilli: see above Clostridial species: esp C. perfringens found in 1/3 samples at 10^6 per gram Coliforms and Enterococcus (faecalis and faecium) = enteric G- rods, present at 10^7 CFU (colony forming unit) per gram, aerobic flora, common cause of UTIs Other Anaerobes: present sporadically @ low #s, >400 species reported in normal feces important factors in intestine =redox potential, pH, flow gases produced = methane and hydrogen Less frequent aerobes = S. aureus, Pseudomonas, Proteus, Klebsiella |
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Establishing Intestinal Flora:
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Fetal Intestine is sterile -> at birth contains a few bacteria, colonized within hours -> breast fed infants mostly have Bifidobacterium -> upon weaning, resembles adult flora
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Intestinal Flora Maintenance:
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ability of bact (path or non path) to proliferate depends on:
Redox Potential (low O2 level) and pH Synerg and Antag of competing microbes: Anaerobes -> reducing conditions Growth factor production used by other bact (vit K) Acid (dec. pH), organic acid (prevent bact growth), and bacteriocin (antibact factors) produced and secreted by intest flora Antibiotic administration can allow growth of pathogens (ex salmonella or shigella) |
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Physiological implications of normal flora metabolic activities:
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1) Bile Acid deconjugation: convert to free bile acids by large intest flora, important for fat absorption
*this is why overgrowth in sm intest can cause overprod of free bile acids and fat malabsorption 2) Source of ammonia via degrad of nitrogenous substances (proteins) in COLON impaired liver function can increase blood ammonia Hepatic Coma - treatment aims to dec normal intest flora with broad spectrum antibiotics, cathartics, enemas 3) convert bile pigments (bilirubin) to urobilin and stercobilin 4) Carbs not absorbed by host are fermented -> decreased pH (helps maintain local flora) |
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Normal skin flora:
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10^3 - 10^4 CFU/cm2
Staphylococcus epidermidis: predominant microorg generally nonpath, except in foreign body presence catheter-related bacteremia is common S. aureus: found in skin and nares, opportunistic Anaerobes (ex Proprionibacterium and Peptococcus)located in deeper dermis follicles (P. acnes implicated in acne) Diptheroids |
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Upper Resp Tract Flora:
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Nose: S. aureus - in 25% healthy individuals
Throat: viridan strep, Neisseria, S. epidermidis Anaerobes: Bacteroides, Fusobacterium, Clostridium, Peptostreptococcus (anaerobic oral strep) |
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Normal GU Flora:
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Vaginal in adult women:
Lactobacillus (for acid pH, antibiotic suppression -> candida albicans overgrowth, not dominant before puberty and after menopause) Vagina can be colonized by fecal flora due to location, can find E. coli and Enterobacter in the introitus (opening), these are pathogens implicated in UTIs and occasional sepsis 15-20% childbearing age women carry group B strep in vagina, important source of newborn sepsis during birth |
