Anaerobes Flashcards
What are the 4 major obligate anaerobe pathogens?
- GP spore forming rods (clostridium)
- GP non-spore forming rods (actinomyces, propionbacterium, eubacterium)
- GN rods (bacteroides, fusobacterium)
- GP cocci (peptococcus, peptostreptococcus)
The body’s normal flora is predominantly _________
Anaerobic
- colonize nearly all mucosal surfaces
- colon: 90% of fecal matter, obligate anaerobes outnumber others by >1000:1
- obligate anaerobes outnumber others in the mouth by 10:1
- oropharynx and lower GIT*
Why are obligate anaerobes able to survive in the mouth?
Oral/viridans streptococci lower the red-ox potential
Most anaerobic infections are _______ in origin
Endogenous
- occur with a break in host defense and low oxygen tension or low red-ox potential is present
Polymicrobial
Anaerobic infections containing both obligate and facultative anaerobes due to tissue contamination with multiple species of host’s microflora
What are the 3 synergistic mechanisms used by anaerobes?
- bacteriodes spp. require vitamin K from nonpathogenic streptococci
- B. asaccharolyticus causes spreading lesions supplied with succinate from klebsiella
- facultative anaerobes (E. coli) provide a better environment for anaerobes by removing O2 and adding reducing substances throughout the infection —> anaerobes then produce leukotoxins and depleting opsonins and complement
What anaerobe does not produce a putrid odor during infection?
Actinomyces
- microaerobic, capnophilic
Bite wounds
Commonly involve anaerobes
- pasteruella (not anaerobic), bacteroides, fusobacterium, paptostreptococcus
What type of sample would you take for an osteomyelitis infection?
Surgical, should include sequestra, bone from infection, or adjacent soft tissue >1 cubic cm in size
- superficial swabs will be contaminated with secondary opportunists!
What is essential for a preliminary diagnosis of anaerobes?
Stained smears
- preferably both a gram stain and cytologic stain (all bacteria will be blue with cytologic)
Specimens from acute bacterial infections usually contain many ________
Neutrophils
- exception: when patient is neutropenic from clostridial myonecrosis
What suggests contamination by normal flora?
Presence of multiple morphological types of bacteria and epithelial cells, few or no neutrophils
What suggests presence of anaerobes?
Multiple morphological types with neutrophils
- only one or 2 morphologic types: aerobes or facultatives present
- multiple types plus negative cultures suggests anaerobes
Bacteroides
- GN rods
- pleomorphic, may be beaded, coccoid, slender
- stain poorly, difficult to see
- sometimes bipolar staining
Clostridium
- GP rods
- large chains
- spores swell sporangium
Fusobacterium
- GN rods
- thin, pale, tapered ends
- cigar/needle shape
Actinomyces
- GP rods
- small, thin, branched filaments or tangled mats
- beaded and poorly visible
- may form sulfur granules
Peptococcus
- GP cocci
- small, singly, pairs, or clusters in pairs/chains
- cannot be distinguished from aerobic cocci
What should not be cultured?
Specimens that might be contaminated with normal flora
- just assume anaerobes are present
Do anaerobes exist in urine?
No!
- urine is toxic/cidal to anaerobes
Acceptable collections
- aspriates from enclosed lesions or body sites normally sterile (potential spaces)
- TTA, lung aspirates
- uterine aspirates
- aspirates of abscesses, deep wound
- tissue obtained from deep infections during debridement
- sequestra, bone biopsies, nearby soft tissue
- blood (not routine)
- aspirates from occeous bullae or frontal sinuses
Unacceptable collections
- swabs of pus from superficial or draining tracts
- urine
- mouth, pharynx, upper airway swabs (should already suspect presence of anaerobes)
- swabs from vagina, cervix, urethra
- feces
- saliva or nasal exudates
- ear swabs
- cerebrospinal fluid, nasotracheal, bronchoscopic aspirates
Syringes
Should empty of air and cap (stick needle into rubber sterile stopper)
Processing
Process immediately
- facultative outgrow anaerobes and syringes absorb air
- if there is a delay, specimens should be kept at room temp in commercial CO2 filled tubes (will survive 72 hrs)
