[Enterobacter amnigenus. An unusual human pathogen]

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.

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.

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 cefoxitine, and 33% to amoxicillin-clavulanic acid. All isolates were susceptible to third-generation cephalosporins, aztreonam, ciprofloxacin, cotrimoxazole and aminoglycosides.

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.