Diagnosis

DIAGNOSIS

Choice of specimens

  • As the non-sporing anaerobes constitute a major por­tion of the normal flora, the specimens must be col­lected with care to avoid contamination from the nor­mal anaerobic flora, situated mainly on mucous mem­branes and in the intestinal tract. The following samples are suitable for culture of the non-spore-forming anaerobes.
    • Pus from abscesses
    • Discharges from wounds (surgical and traumatic)
    • Direct pleural aspirates
    • Peritoneal aspirates
    • Joint fluids
    • Urine if taken by suprapubic puncture
    • Tissue specimens (biopsy, necropsy and post-opera­tive)

Collection of specimens

  • Specimens for the isolation of these strict anaerobes should be placed immediately in an oxygen-free con­tainer, especially small pieces of tissue or material taken on swabs.
  • Larger pieces of tissue (over 2 cm3) usually main­tain an anaerobic microenvironment deep in the tissue and can be placed in an air-tight jar for transportation.
  • Fluid specimens can be collected in a sterile syringe, the air expelled and the needle bent over or plugged. However, if the specimen cannot be processed within an hour, a fluid specimen should be placed in an oxy­gen-free tube or vial.
  • All specimens for anaerobic cul­ture should be processed within a few hours of collec­tion.
  • It is best to keep the specimens at ambient tem­perature rather than in the refrigerator, as oxygen absorption is greater at lower temperatures.
    • Direct examination
      • Gram-stained smears of the specimens are useful as a screening process, although many of these anaerobes are not morphologically distinctive.
      • Dilute carbol fuchsin (4-8 minutes) stained smears are more useful for Bacteroides and Fusobacterium species as they tend to stain faintly with the Gram-stain.
      • Fusobacterium necrophorum in clinical specimens is long and filamentous (about 1µm in diameter) and characteristically stains in an irregular manner.
      • Bacteroides nodosus is a large rod characterised by the presence of terminal enlargements at one or both ends (barbell or club shaped).
    • FAT is reported as being specific and sensi­tive
    • By Isolation and identfication in anerobic media
    • By animal inoculation
      • Mice, rats and guinea pigs inoculated with cultures of B. nodosus will produce abscess and sepsis.
      • Inoculate rabbit subcutaneously with material suspected for F. necrophorum - produces lesions throughout the body.
  • Differential diagnosis should be made with strawberry foot rot caused by Dermatophilus species, FMD and pyogenic infections associated with Corynebacterium pyogenes.
Last modified: Monday, 4 June 2012, 5:45 AM