Antimicrobial susceptibility patterns (antibiograms) as an aid in differentiating Citrobacter species

Area of Science:

• Clinical microbiology
• Bacterial taxonomy
• Antimicrobial resistance

Background:

• The hydrogen sulfide-negative Citrobacter group presents a significant taxonomic challenge.
• Previous classifications include Padlewskia, Levinea, and atypical Enterobacter cloacae.
• Accurate identification is crucial for effective patient management.

Purpose of the Study:

• To investigate the utility of antibiograms in differentiating hydrogen sulfide-negative Citrobacter species.
• To establish clear criteria for distinguishing between Citrobacter diversus and Citrobacter freundii.

Main Methods:

• Clinical isolates were classified as C. diversus (40 strains) or C. freundii (25 strains) based on Ewing and Davis criteria.
• Antimicrobial susceptibility testing was performed using the agar-dilution method.
• Susceptibilities to ampicillin, carbenicillin, and cephalosporins were evaluated.

Main Results:

• Citrobacter diversus showed high resistance to ampicillin (97.5%) and carbenicillin (87.5%), but susceptibility to cephalosporins (≥90%).
• Citrobacter freundii exhibited moderate susceptibility to ampicillin (25%), susceptibility to carbenicillin (92%), and resistance to cephalosporins (≥92%).
• These antibiotic susceptibility profiles allowed for 90% accurate separation of the two species.

Conclusions:

• Antibiogram profiles provide a reliable method for distinguishing C. diversus from C. freundii.
• This approach aids in resolving the taxonomic ambiguity within the hydrogen sulfide-negative Citrobacter group.
• Accurate species identification through antimicrobial susceptibility testing has significant clinical implications.