John Chin is an Internal Medicine Physician; Tyler Warkentien and Karl Kronmann are Infectious Disease Physicians; all at Naval Medical Center Portsmouth in Virginia. Brendan Corey and Erik Snesrud are Researchers in the Multidrug-Resistant Organism Repository and Surveillance Network at Walter Reed Army Institute of Research in Silver Spring, Maryland. Correspondence: John Chin (chinjoh@gmail.com)
Author disclosures The authors report no actual or potential conflicts of interest with regard to this article.
Disclaimer The opinions expressed herein are those of the authors and do not necessarily reflect those of Federal Practitioner, Frontline Medical Communications Inc., the US Government, or any of its agencies. This article may discuss unlabeled or investigational use of certain drugs. Please review the complete prescribing information for specific drugs or drug combinations—including indications, contraindications, warnings, and adverse effects—before administering pharmacologic therapy to patients.
Additionally, none of the isolates carried the nim or bft toxin genes. Although the nim gene is associated with metronidazole resistance,its presence does not invariably result in resistant strains of B fragilis; in fact, metronidazole resistance is relatively uncommon, with the majority of B fragilis showing < 1% resistance, based on CLSI breakpoints (≥ 32 mg/L).13,20,21 However, one recent epidemiologic study on anaerobic wound isolates from Iraq and Afghanistan casualties found that 12% (2/17) of B fragilis isolates were resistant to metronidazole.15 Given the improvement of the patient’s symptoms while on metronidazole, it is likely that the B fragilis was susceptible. Nevertheless, susceptibility testing with minimum inhibitory concentrations is necessary to verify this result. Also, although enterotoxigenic strains of B fragilis have been associated with bloodstream infections, our patient’s isolates lacked the 3 subtypes of B fragilis enterotoxin gene.22
Conclusions
We report a case of B fragilis bacteremia and vertebral osteomyelitis complicated by challenges in anaerobic identification and sensitivities that led to brief use of a possibly inactive antimicrobial and the subsequent use of carbapenem therapy, which may have been avoided if susceptibility testing were more readily available. This case led to changes in our hospital’s processing of anaerobic isolates to include susceptibility testing on request.
Acknowledgments
We thank Keith Thompson, MD (staff pathologist, Naval Medical Center Portsmouth Virginia), for providing the pathology images from the initial vertebral biopsy, and Dr. Kate Hinkle (director, Multidrug-Resistant Organism Repository and Surveillance Network, Silver Spring, Maryland ) for providing the whole genome sequencing results from the B fragilis isolates.
