Bacteraemia caused by non-freundii, non-koseri Citrobacter species in Taiwan

This study analysed the clinical characteristics of bacteraemia due to unusual Citrobacter species. All non-freundii and non-koseri Citrobacter isolates were identified to species level by two commercial identification methods and 16S rRNA gene sequence analysis. A total of 306 patients with Citrobacter spp. bacteraemia were identified from January 2000 through December 2009. Four patients (1.3%) had C. braakii bacteraemia, and one had C. amalonaticus and C. sedlakii sepsis, respectively. Misidentification as non-freundii and non-koseri Citrobacter spp., which occurred in eight isolates with the Phoenix automated system PMIC/ID-30 and three with the Vitek II system, occurred in five of six infection episodes. Among the six patients with bacteraemia caused by non-freundii and non-koseri Citrobacter spp., five (83.3%) had healthcare-associated infection and five (83.3%) infections were secondary to intra-abdominal infection. Cancer and liver cirrhosis were the commonest underlying diseases. An attributable mortality was 33.3%. Antimicrobial susceptibility testing showed that the resistance patterns varied among different Citrobacter species. Non-freundii and non-koseri Citrobacter species are difficult to identify and are a rare cause of intra-abdominal infections with secondary healthcare-associated bacteraemia in immunocompromised patients.