Anaerobes

Question 0

Anaerobic infection species

Answer 0

Can predict species based on location!
- almost all anaerobic from patient’s endogenous flora

Above diaphragm (ex oral): penicillin sensitive, mixed Gram + cocci, Gram (-) bacilli
Below diaphragm (ex intra-abdominal): penicillin resistant (B fragilis), mixed Gram (-) bacilli (colonic)

Skin/cellulitis: Clostridia

Question 1

Overview of anaerobes

Answer 1

True anaerobes - cannot tolerate high ox-red potential, superoxide, H2O2
- lack superoxide dismutase, usually lack catalase

Major part of normal flora (GI, female, oral) -> abcesses

• normally mixed (anaerobe or microaerophile) vs single species (aerobic or facultative aerobes) - look if there are multiple aerobes!
• foul discharge, gas

Normal tissue - high O2 (ox-red potential) -> suppress growth
Susceptible tissue - low O2, ox-red due to wound, impaired perfusion or necrosis

Predispositions
- aspiration, GI surgery, abortion, bite, trauma, malignancy, poor dental hygiene

Question 2

Anaerobic methodology

Answer 2

Do NOT expose to air!
-> direct into special vial (ex thioglycollate = reducing agent)
- do not submit oral or fecal samples
Anticipate mixed reactions - may not detect all pathogens
Gram stain -> spores, morphology (ex Fusobacterium)
Culture -> colony morphology (ex Prevotella)
- sensitivity assays not as reliable
Metabolism - ex fatty acid production

Question 3

Bacterium fragilis

Answer 3

Most abundant anaerobic Gram (-) bacillus
- tolerates traces of O2
- pleiomorphic
Feces (10>11 CFU/g) -> extraintestinal ->
- intra-abdominal (bowel rupture)
- female (abcess post abortion, IUD, delivery)
- septicemia (+ Clostridium perfringans = 80% of anaerobic sepsis, this is still only 8% of total though due to aerobic..)

RESISTANT TO PENICILLIN
resistant to bile

Virulence = capsule
Mixed with E coli = increased virulence

Question 4

Prevotella melaninogenicus

Answer 4

Anaerobic Gram (-) rod
Oral -> periodontal, occassional genital

Sensitive to penicillin
More sensitive to O2 than B fragilis (difficult to culture)

Name = black hemin (-> cytochrome synthesis, necessary for growth)
- aka Bacteroides melaninogenicus

Question 5

Fusobacterium

Answer 5

Anaerobic Gram (-) rod
 - tapered ends, very skinny (-> "spindle" shaped)

Oral -> lung, pleuropulmonary
(second species intestinal -> abdominal)

Sensitive to penicillin
Sensitive to O2 (difficult to culture)

Question 6

Corynebacterium

Answer 6

non-diptheriae = diptheroids

Pleiomorphic anaerobic Gram + rod
- some strains aerotolerant
Normal skin flora -> contaminates cultures
- occassional endocarditis

Question 7

Lactobacillus

Answer 7

Normal flora of intestine, vagina

• > low pH, prevent pathogen growth
• non-pathogen!
• used for yogurt, saurkraut, etc…

Question 8

Actinomyces

Answer 8

Anaerobic Gram (+) rods

• branching
• sulfur granules = characteristic microcolonies + debris -> yellow
• colonies = “molar tooth” appearance

Usually after trauma, surgery
Normal oral -> dental, oral, lung infections
Normal GI -> abdominal
- sinus tract

Question 9

Anaerobic cocci

Answer 9

Pseudostreptococcus - chains of Gram + cocci but obligate anaerobe

• widely involved in infections
• oral (-> pulmonary, brain abcess), UG -> gyn, GI

Pseudostaphylococcus - clumps of Gram + cocci but obligate anaerobe
- oral, URI -> lung, GI -> abdominal

Veillonella - anaerobic Gram (-) cocci
- not pathogenic, commensal

Question 10

Anaerobic treatment

Answer 10

Drain the abcess (no antibiotics work!)

Penicillin (unless B fragilis, abdominal)
B fragilis -> Clindamycin, Cephalosporins (ex cefoxitin)
Chloramphenicol = static
Metronidazole/Flagyl

Add aminoglycoside if mixed aerobic/anaerobic
- gentamycin + cefoxitin or clindamycin

Question 11

Propionibacterium

Answer 11

Anaerobic Gram + bacilli

Skin -> acne

Question 12

Prophyromonas

Answer 12

Anaerobic Gram - rod

Oral, periodontal

Question 13

Overview of anaerobes

Answer 13

Spores -> Clostridium

Gram + rods - Propionibacterium, Actinomyces, (bifido, lacto)
Gram (-) rods - spirochetes if motile
- nonmotile - Bacteroides, Fusobacterium, Prevotella, Porphyromonas
Gram + cocci - Peptostreptococcus
Gram (-) cocci - Viellonella

Narrow within category via gas chromotography of fatty acid products

Question 14

Oral pathogens

Answer 14

• > brain abcess, sub or epidual empyema
• > otitis media -> meningitis
• > dental, periodontal

Prevotella
Peptostreptococcus
Actinomyces
Fusobacterium

Streptococcus viridans (aerobe)

Human bite: oral anaerobes, Eikenella corrodens

Question 15

Respiratory pathogens

Answer 15

URI -> facial abscess, CNS, sinusitis
-> aspiration pneumonia, abscess, bronchiectasis

Prevotella
Peptostreptococcus
Fusobacterium
Actinomyces (trauma, URI only)

Aerobes:
Streptococcus
Staphylococcus (URI or nosocomial pulm)
Enterobacteriae (nosocomial pulm only)

Question 16

Bacteremia pathogens

Answer 16

90% are aerobic

Anaerobes - 80% are Clostridium perfringans + B fragilis
also Fusobacterium, Peptostreptococcus

Question 17

Abdominal pathogens

Answer 17

• > peritonitis, abscess (rupture)
• > liver, subphrenic abscess
• > appendicitis

Bacteroides fragilis (penicillin resistant!)
Fusobacterium
Peptostreptococcus
Clostridium

Aerobes:
E coli
Klebsiella
Proteus
Pseudomonas
Group D Strep
Enterobacter
Staphylococcus (liver rectal)

Question 18

Gyn pathogens

Answer 18

• > abscess post procedures, delivery, IUD, abortion
• > endometritis

B fragilis
Prevotella
Fusobacterium
Peptostreptococcus

Aerobes:
E coli
Proteus
Staphylococcus
Group B streptococcus