Micro: Anaerobic Bacterial Inf Flashcards
What are some important definitions?
anaerobe: fails to grow on solid media in 10% CO2 in air (18% oxygen)
facultative: grows in presence of absence of air
microaerophilic: grows poorly aerobically but grows in 10% CO2 in air, also grows anaerobically
most clinically significant anaerobes are aerotolerant (2-8% oxygen) b/c they produce superoxide dismutase, some actually grow aerobically (c. tertium)
What are some features of normal flora on skin and mucosal surfaces?
coexistent aerobic flora consume 02
microhabitats protected from oxygen
highest colony counts in the colon
change w acchlorhydria, abx, antacids, age, loss of teeth, pregnancy
What are important functions of normal flora on skin and mucosal surfaces?
colonization resistance, vitamin K production, deconjugate bile acids, modify drugs, metabolize dietary nutrients, stimulate mucosal immunity
What are host factors which permit inf w anaerobes to occur?
break in anatomic barrier
immune mechanisms not as important w anaerobes
decreased redox potential of tissue: obstruction/stasis, tissue anoxia or destruction, foreign body, burn, vascular insufficiency, concomitant aerobic inf
specific clinical predispositions
What are specific clinical predispositions to inf w anaerobes?
diabetes
malignancy: colon, uterus, lung, leukemia
surgery: oral, head/neck, GI, female pelvis
oral, GI, genital tract dz or trauma
aspiration of oral or gastric contents
human or animal bites
AIDS, Downs, acatalasemia: necrotzing gingivitis
What are bacterial factors that permit inf w anaerobes to occur?
size of inoculum
synergy w aerobic/facultative bacteria
virulence factors: adherence/invasion, enzymes/toxins, surface structures, short chain FAs inhibit phagocytic killing
What are anaerobes most commonly involved in invasive clinical inf?
b. fragilis group prevotella sp, porphyromonas sp. (pigmented, fluoresce) fusobacterium nucleatum peptostreptococcus c. perfringens, c. ramosum, c. septicum actinomyces sp.
What are features of anaerobic inf in the CNS?
brain abscesses (often multiple), subdural empyema
associated with: contiguous otitis/mastoiditis/sinusitis, lung abscess, congenital R to L shunt
often curable w/o surgery
only rarely meningitis (represents rupture of abscess)
What are features of head and neck inf by anaerobes?
chronic otitis media, chronic sinusitis, peritonsillar abscess = Lemmiere’s syndrome - look for jugular vein abscess, odontogenic infections, deep fascial space infections = Ludwig’s angina - swelling of mouth/neck, drooling
vincent’s angina = acute necrotyzing ulcerative gingivitis
What are the features of pleuropulmonary infections by anaerobes?
periodontal dz + aspiration
pneumonia in dependent segments, abscess, empyema
fusobacterium, prevotella, peptostreptococcus most common
look for air fluid levels on CXR
What are the features of intraabdominal inf by anaerobes?
appendicitis, diverticulitis, liver and intermesenteric abscesses, secondary peritonitis, pylephlebitis, biliary tract inf
What are the features of female genital tract inf by anaerobes?
bacterial vaginosis, abscesses, endometritis and salpingitis, postop wound inf, septic abortion, septic pelvic, thrombophlebitis
IUD? - actinomycosis or eubacterium nodatum
What are the types of soft tissue inf caused by anaerobes?
diabetic foot inf, decubitus ulcers, bite wounds, burn wounds, necrotizing fasciitis, gas-forming cellulitis, clostridial myonecrosis (gangrene), Fournier’s gangrene = scrotum
Where does osteomyelitis happen as a result of anaerobic inf?
diabetic or ischemic foot ulcer, decubitus ulcer, skull/facial bones, contaminated open fracture
What are the features of bacteremia as a result of anaerobic inf?
often polymicrobial
suggests abdominal or female pelvic pathology
c. septicum: colon cancer, leukemic cecitis
c. perfringens, c. novyi: soft tissue inf and fatal bacteremia in IVDA
