Emergence of metronidazole-resistant Bacteroides fragilis, India.

485 Vol. 7, No. 3, May–June 2001 Emerging Infectious Diseases References 1. Barros MLB, Boecken G. Jungle yellow fever in central Amazon. Lancet 1996;348:969. 2. Ministry of Health. Notified cases of yellow fever by state, Brazil. Brasilia: National Epidemiology Center; 2000. 3. Vasconcelos PFC, Rodrigues SG, Degalier N, Moraes MAP, Rosa JFST, Rosa EST, et al. An epidemic of sylvatic yellow fever in the Southeast Region of Maranhão State, Brazil, 1993-1994: epidemiological and entomological findings. Am J Trop Med Hyg 1997;57:132-7. 4. Deubel V, Huerre M, Cathomas G, Drouet M-T, Wuscher N, Le Guenno B, et al. Molecular detection and characterization of yellow fever in blood and liver specimens of a non-vaccinated fatal human case. J Med Virol 1997;53:212-7.

dime, cefotaxime, and ciprofloxacin. B. fragilis was resistant to metronidazole (MICs, 256 µg/mL) by both standard broth dilution method and E-test (AB Biodisk, Solne, Sweden). The isolate was also resistant to cefotaxime and ceftazidime. However, it was sensitive to chloramphenicol, clindamycin, and imipenem.
Primary bacteremia caused by anaerobic organisms accounts for <5% of septicemia in cancer patients (3). Chemotherapy is a known predisposing factor for anaerobic bacteremia because it causes gastrointestinal ulceration, which permits anaerobes to enter circulation (4).
Anaerobic bacteremia is usually polymicrobial in etiology and has a high death rate (4). In this case, both bacterial isolates were resistant to the empirical treatment. Delay in initiating appropriate therapy was perhaps a major contributor to the patient's death.
Metronidazole is the drug of choice for empirical coverage of anaerobic infections. The precise incidence of resistance to metronidazole in B. fragilis isolates is difficult to estimate (5), since routine antimicrobial sensitivity testing of anaerobes is not being done by most laboratories in the world. Published articles reveal only a few reported cases of B. fragilis that were resistant to metronidazole (6-10). Although the incidence of resistance to penicillin, cephalosporins, and clindamycin is increasing dramatically, no resistance to metronidazole in B. fragilis was found in some large-scale studies done throughout the world (11,12).
The true incidence of metronidazole resistance in India too is possibly underestimated since antimicrobial sensitivity testing is not being done routinely. However, we are conducting antimicrobial susceptibility testing of all anaerobic isolates in our institute. In a previous study we conducted (13), contrary to this report, none of 32 clinical isolates belonging to the family Bacteroidaceae obtained over a 5-year period were resistant to metronidazole.
Recently, the anaerobic reference unit in the UK noted a possible increase in the incidence of metronidazole resistance in B. fragilis, an observation that would have major implications for clinical microbiology laboratories, as well as for prophylactic and treatment regimens (5).
There is now a growing debate whether in vitro susceptibility testing should be performed for all Bacteroides isolates to guide antimicrobial therapy. The acquisition of metronidazole resistance by B. fragilis reported here from India emphasizes the need for a study to assess more accurately the susceptibilities of clinical isolates of Bacteroides spp.
Diagnostic microbiology laboratories and clinicians should be aware that the incidence of metronidazole resistance in clinically significant anaerobes may be increasing (5). Since antimicrobial resistance in anaerobes varies from one hospital to another and between different geographic locations, all hospitals should survey their sensitivity patterns and report any emerging resistance.

Proper Nomenclature for the Human Granulocytic Ehrlichiosis Agent
To the Editor: In their recent article, "Antigenic variations in vector-borne pathogens," Barbour and Restrepo discuss the outer membrane protein components of Anaplasma marginale and related bacteria (1). Citing a reference by Zhi et al. (2), they state that Ehrlichia granulocytophila is the agent of human granulocytic ehrlichiosis (HGE).
The use of new names and combinations not widely recognized for genera and species lends increasing confusion to a group of bacteria already in taxonomic disarray. Several other species names have been suggested for the HGE agent since the initial description of the clinical illness caused by this agent and the in vitro technique used to isolate the agent in blood samples (3,4). Both E. phagocytophila and E. equi are genetically nearly identical to the HGE agent, and the three are probably conspecific. Thus, most scientists in the field today would support use of the name Ehrlichia phagocytophila to describe these bacteria.
Recent phylogenetic analyses show that E. phagocytophila strains align into a clade that includes Anaplasma marginale, the historical precedent in this grouping. Such phylogenetic analyses, which are also supported by comparative antigenic and biological studies, have resulted in a proposal for reclassification of several Ehrlichia spp., including E. phagocytophila, into the genus Anaplasma (5). Until a cogent reclassification based on objective criteria is firmly accepted, the creation and use of new scientific name combinations for a single bacterium yield clinical and laboratory confusion and should be avoided.