Rapid presumptive identification of Citrobacter diversus as an aid in controlling infections.

During an outbreak of neonatal meningitis caused by kanamycin-resistant Citrobacter diversus, a field procedure for presumptive identification of the organism was evaluated, and using it resulted in the early recognition of patients colonized by the epidemic strain of C. diversus. Rectal and nasopharyngeal specimens were plated and incubated on MacConkey agar containing 10 micrograms of kanamycin per ml. After 18 h of incubation, lactose-nonfermenting colonies present on the selective medium were picked and identified 8 h later with the following biochemical tests: indole, adonitol, dulcitol, citrate, and triple sugar iron agar. This presumptive identification of C. diversus was later confirmed for all cases by conventional testing with a complete set of biochemicals. In 1 week, 253 specimens from patients were processed with this technique, and 49 strains of C. diversus were identified. The rapid identification of C. diversus and transfer of carriers into appropriate cohorts resulted in a 64% reduction in the prevalence of colonization.