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Anaerobic Bacteriology

Published: June 2012

Hot Topic Q&A is an opportunity for viewers to submit questions to the Hot Topic presenter. The opportunity to submit questions for this topic is now closed.

The following questions were submitted by viewers and answered by the presenter, Jon Rosenblatt, MD, a Professor of Medicine and Microbiology, as well as a consultant in the Division of Clinical Microbiology at Mayo Clinic in Rochester, Minnesota. 

Questions are presented as submitted (unedited).

  1. Do you culture aspirates from sinus cultures collected in surgery for anaerobes?


  2. I would like to have some more information about identifying anaerobes in mixed cultures with aerobic bacteria. Maybe the presenter could help with that.

    This is complicated because the decisions as to how much work to do on a mixed culture are somewhat arbitrary and based on the experience of the technologist. The general principle (see slides #16-17) is to fully identify the isolates only when a likely pathogen is present with no other, or a limited number of other likely pathogens.

    Following is a scheme for identification of anaerobes in mixed culture:

    (a) Partial Identification for sources other than in (b). Any number of anaerobes with an aerobic culture that includes usual flora: Report by Gram stain only with suggested morphology; ie, “resembling fusobacteria”

    (b) Partial plus Identifications for following specimens sources:

    • CSF
    • CNS fluid, Pericardial fluid or tissue
    • Synovial, Joint fluids
    • Bone marrow
    • CNS tissues
    • Lung
    • Pleura tissues
    • Bone
    • Joint tissues
    • Organ specific material (tissue or abscess)

    For >3 isolates in mixed culture, fully identify anaerobic Gram-negative bacilli and probable Clostridium

    (c) Mixed flora other than in (b) or blood
    Mixed flora, Anaerobes present, not further identified

  3. Are there drugs of choice that can be reported out if sensitivities are not routinely done in Lab?

    No. If the lab does not do antibiotic sensitivity testing for anaerobes, the clinician should consult the literature for empiric choices for treatment.