Enterobacter amnigenus. An unusual human pathogen

BACKGROUND: Enterobacter amnigenus is a bacteria with doubtful pathogenicity. The observation of a patient with a well-documented E. amnigenus infection has prompted us to review the pathology caused by this microorganism. METHODS: Retrospective evaluation of the clinical charts of patients with any isolate positive for E. amnigenus over a period of 46 months. Based on the clinical data, presence or absence of other causal microorganisms and/or alternative diagnosis, E. amnigenus was classified as definitive, probable, or improbable cause of infection. RESULTS: We analyzed 15 E. amnigenus isolates, representing 0.97 of 10,000, the total bacterial isolates in our laboratory for this period, and 0.52% of those corresponding to Enterobacter sp. We were able to clinically evaluate E. amnigenus in 7 patients, in whom infection by this microorganism was classified as definitive in 4, probable in 1, and improbable in 2. Antibiotic susceptibility studies showed a resistance level of 83% to ampicillin, 75% to cefazoline and cephoxitine, and 33% to amoxicillin-clavulanic acid. All isolates were susceptible to third-generation cephalosporins, aztreonam, ciprofloxacin, cotrimoxazole and aminoglycosides. CONCLUSIONS: E. amnigenus cause well-documented bacterial infection in man. Thus, isolation of this microorganism should not be considered as a contaminant or simple colonizer. The clinical behavior and antimicrobial susceptibility of E. amnigenus is similar to that of E. cloacae, a taxonomically-related species.