Citrobacter farmeri bacteremia in a child with short-bowel syndrome

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.

Fatal Citrobacter farmeri meningitis in a patient with nasopharyngeal cancer

We describe the case of an adult male with nasopharyngeal carcinoma who had meningitis caused by Citrobacter farmeri. The isolate was confirmed as C. farmeri by two commercial identification systems and 16S rRNA gene analysis. The patient developed multiorgan failure and died despite antibiotic treatment with in vitro active agents (ceftriaxone and meropenem).

Cloning and sequencing of the beta-lactamase gene and surrounding DNA sequences of Citrobacter braakii, Citrobacter murliniae, Citrobacter werkmanii, Escherichia fergusonii and Enterobacter cancerogenus

To further identify the origins of plasmid-mediated cephalosporinases that are currently spreading worldwide, the chromosomal beta-lactamase genes of Citrobacter braakii, Citrobacter murliniae, Citrobacter werkmanii reference strains and of Escherichia fergusonii and Enterobacter cancerogenus clinical isolates were cloned and expressed into Escherichia coli and sequenced. These beta-lactamases had all a single pI value >8 and conferred a typical AmpC-type resistance pattern in E. coli recombinant strains. The cloned inserts obtained from genomic DNAs of each strain encoded Ambler class C beta-lactamases. The AmpC-type enzymes of C. murliniae, C. braakii and C. werkmanii shared 99%, 96% and 95% amino acid sequence identity, respectively, with chromosomal AmpC beta-lactamases from Citrobacter freundii. The AmpC-type enzyme of E. cancerogenus shared 85% amino acid sequence identity with the chromosomal AmpC beta-lactamase of Enterobacter cloacae OUDhyp and the AmpC-type enzyme of E. fergusonii shared 96% amino acid sequence identity with that of E. coli K12. The ampC genes, except for E. fergusonii, were associated with genes homologous to regulatory ampR genes of other chromosomal class C beta-lactamases that explain inducibility of beta-lactamase expression in these strains. This work provides further evidence of the molecular heterogeneity of class C beta-lactamases.