Citrobacter koseri (syn. C. diversus): biotype, serogroup and drug resistance patterns of 517 strains

The names Citrobacter koseri and C. diversus are synonyms for a species of enterobacterium with a particular ability to cause neonatal meningitis. 517 strains belonging to this species were examined using biotyping and serotyping techniques. 40% of the strains belonged to serogroups O2 and O1 and 72% belonged to biotypes d and a. Strains isolated from cerebrospinal fluid belonged to several different serogroups and biotypes but serogroups O2 and O3 and biotypes d and a were the most common. All the strains were resistant to ampicillin, 42% were resistant to neomycin/kanamycin and 38% were resistant to cephaloridine. 37% of the strains were resistant to three or more drugs.