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Flashcards in L 72 Anaerobic Bacterial Infections Deck (19):

Why is O2 deadly to anaerobic bacteria?

They lack enzymes to deal with oxidative stress such as:
Superoxide dismutase-radical O2 into normal O2
Catalase-hydrogen peroxide into water
Peroxidase-oxidation by hydrogen peroxide


How do anaerobic bacteria produce energy?

They are fermenters
This process produces acids that often produce smells
Can also use other molecules besides O2 at end of electron transport chain


What type of bacteria predominates in the human body?

Anaerobic bacteria predominate
We didn't know they were there for long time because we didn't know to culture for them


Why are we interested in anaerobes?

Many are assoc. with infection


Anaerobe epidemiology

All ages
Kids: URT, head, neck
Commonly in patients with chronic infections
Most in abscesses, wounds, OB/GYN infections

Predisposing conditions:
Compromised circulation, diabetes, trauma
Prefer acidic conditions-necrotic tissue is acidic-lactic acid fermentation

Endogenous: often leak from gingiva, gut

Exogenous: soil, water, food


Can anaerobes survive in air?

Yes, but they cannot replicate
Tolerance depends on species and genera


Anaerobes general features

No O2 detoxifying enzymes
Putrid odor
Majority infections-polymicrobial cause disease by synergism
Intra-abdominal abscesses: coliforms + anaerobes
-Coliforms=CHEEK (Citrobacter, Hafnia, Enterobacter, E. coli, Klebsiella) all g(-)


Most commonly isolated anaerobes

Bacteroides fragilis
Pigmented prevotella
Fusobacterium g(+)
Peptostreptococcus g(-)


What is the most common, non-spore forming opportunistic anaerobic pathogen?

Bacteroides fragilis


Bacteroides Fragilis characteristics

Gram (-) bacillus
Non-spore forming
Very common opportunistic pathogen
Found in colon
Bile resistant
Hardy, easily cultured
SOD, inducible catalase (exception to rule)
LPS–less endo-toxicity than others
PSA (polysaccharide A capsule)
-Phase variation: 1) Essential to abscess formation (attachment to peritoneal mesothelium), 2) Inhibits complement-mediated killing


Bacteroides fragilis clinical manifestations

Abscess formation: capsule adheres to peritoneal mesothelium, area surrounded by fibrous-collagen capsule; PSA only capable of abscess formation

Deep pain and tenderness below diaphragm
Fever and findings of acute abdomen
Infection can spread


Prevotella characteristics

Normal microbiota of mouth
G (-) coccobacilli
Abscesses of mouth, pharynx, brain, lung, PID, tubo-ovarian abscesses
Encapsulated, LPS–strong endotoxin, produce IgA, IgG, IgM proteases


Fusobacterium characteristics

Normal microbiota of mouth
G (+) cigar-like form or like a fuselage
Lemierre's syndrome: occlusion of the jugular vein from abscess
LPS–strong endotoxin


What makes Peptostreptococcus unique?

It is the only anaerobic gram (+) coccus seen in clinical infections


Peptostreptococcus characteristics

Normal microbiota of mouth, colon, female genital tract
Associated with brain abscesses when with viridans streptococci


Clues for diagnosing anaerobic infections

Infection contiguous to a mucosal surface
Putrid odor and gas formation
Abscess formation or tissue necrosis
Antibiotic ineffectiveness


What imaging can be used to detect infection?

CT or MRI are useful
Think cellulitis, fasciitis, myonecrosis


General guidelines for bacterial causes in regard to being above or below the diaphragm

Above the diaphragm:
Fusobacterium, Prevotella, Peptostreptococci

Below the diaphragm:
Bacteroides fragilis


Anaerobe bacterial infection treatment

Surgical drainage of abscesses, debridement
Antibiotics for B. fragilis: Metronidazole, Carbapenems, Beta-lactam beta-lactamase inhibitor
Reistance to CLindamycin and fluorquinolone

Antibiotics for Fusobacterium, Prevotella, Peptostreptococci:
Metronidazole, Clindamycin, Amoxicillin-clavulanate
Resistance to all beta-lactams (penicillins and cephalosporins)