[Taxonomy of Citrobacter rods found in human specimens]

The aim of this study was the identification of 181 Citrobacter strains on the basis of the recently proposed taxonomic changes of Brenner. All strains were isolated from diarrhoeic patients; 124 strains were originally sent for identification to Laboratory of Enterobacteriaceae DB NIH, 57 strains was isolated in Czech Republic. Citrobacter isolates were initially identified as C. koseri (3 strains), C. amalonaticus (1 strain) or as members of the C. freundii complex (177 strains). Additionally some biochemical tests were performed. The ability to grow in medium containing KCN, lysine decarboxylase production, lactose fermentation and PYR test were examined. Strains belonging to the C. freundii complex were identified to the species level by biochemical methods on the basis of the results of Brenner, who found some tests to be useful in separating Citrobacter species. These test included citrate and acetate utilization, arginine dihydrolase and ornithine decarboxylase activities, motility, urease production, esculin hydrolysis, and acid production from sucrose, dulcitol, melibiose, raffinose and salicin. On the basis of the criteria described above, 96.6% of the strains tested could be assigned to one of the recently named species of C. freundii complex. Using biochemical tests suggested by Brenner we were able to identify Citrobacter strains members of newly recognised species. A five-test system is proposed to identify the most frequently encountered species currently residing in the C. freundii complex.