Antimicrobial Susceptibility Patterns (Antibiograms) as an Aid in Differentiating Citrobacter Species

Abstract

The hydrogen sulfide-negative Citrobacter group represents a taxonomic problem. Various investigators have proposed such designations as Padlewskia, Levinea, atypical Enterobacter cloacae, H2S-negative variants of Citrobacter, Citrobacter koseri and Citrobacter diversus. This problem has been investigated with emphasis on antibiograms as a means of discrimination. Clinical isolates fitting the designation Citrobacter were studied and, using the criteria of Ewing and Davis, separated into two groups: C. diversus (40 strains) or C. freundii (25 strains). Susceptibilities to ampicillin, carbenicillin, cefazolin, cephaloridine and cephalothin were determined by the agar-dilution method. C. diversus strains were resistant to 8 mug/ml ampicillin (97.5%) and 32 mug/ml carbenicillin (87.5%), and were susceptible to 8 mug/ml cephalosporins (greater than or equal to 90%). C. freundii strains were moderately susceptible to 8 mug/ml ampicillin (25%) and susceptible to 8 mug/ml carbenicillin (92%), and were resistant to 8 mug/ml cephalosporin (greater than or equal 92%). Using these data one can separate C. diversus from C. freundii with 90% accuracy.

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

“…Holmes et al (1974) and Southern & Bagby (1977) reported that most strains of C. koseri were resistant to ampicillin and sensitive to cephaloridine and suggested that drug resistance was valuable in distinguishing between C. koseri and C. freundii. In the present study, however, 380 of strains were resistant to cephaloridine.…”

A brief insight into Citrobacter species - a growing threat to public health

“…However, only experimental and in silico serotyping systems for Citrobacter detection have been developed to manage infections caused by it (Qian et al, 2018). It has been proposed that the affinity of C. koseri for nerve tissues and its propensity to induce meningitis and abscesses were related to a unique 32 kilodalton (kDa) outermembrane protein (Southern and Bagby, 1977;Kline et al, 1988;Li et al, 1990).…”