Two epidemiologically related cases of Rahnella aquatilis bacteremia

Rahnella aquatilis was isolated from the blood cultures of two patients who were in different units of the same hospital. Both isolates were susceptible to aminoglycosides, fluoroquinolones, cotrimoxazole, piperacillin, third generation cephalosporins and amoxicillin-clavulanate, but resistant to amoxicillin, ticarcillin, and first generation cephalosporins. The synergistic activity of amoxicillin and clavulanic acid suggested the presence of a beta-lactamase, confirmed by a positive nitrocefin test and by analytical isoelectric focusing. Pulsed-field gel electrophoresis and ribotyping with the pKK3535 probe showed that the isolates shared the same banding pattern. The results of an epidemiological study suggested that an in-house total parenteral nutrition solution might be the source of this unusual gram-negative rod.