Routine disc diffusion antimicrobial susceptibility testing of Clostridium difficile and association with PCR...

Area of Science:

• Clinical microbiology
• Infectious diseases
• Antimicrobial resistance

Background:

• Reduced susceptibility to metronidazole and vancomycin in Clostridium difficile is a growing concern.
• Simple and reliable antimicrobial susceptibility testing (AST) methods are needed for routine clinical use.

Purpose of the Study:

• To evaluate a published disc diffusion method for Clostridium difficile susceptibility testing.
• To correlate zone diameter breakpoints with EUCAST epidemiological MIC cut-off values.

Main Methods:

• Disc diffusion testing was performed on 2702 Clostridium difficile isolates.
• Metronidazole and vancomycin zone diameters were recorded and analyzed.
• Results were compared against established breakpoints and PCR ribotype 027 prevalence.

Main Results:

• Fifteen isolates showed reduced susceptibility to metronidazole (zone diameter <23 mm).
• Five isolates showed reduced susceptibility to vancomycin (zone diameter <19 mm).
• Clostridium difficile PCR ribotype 027 isolates exhibited smaller zone diameters compared to non-027 isolates.

Conclusions:

• The disc diffusion method is a simple, inexpensive, and effective tool for detecting Clostridium difficile with reduced susceptibility to metronidazole and vancomycin.
• Published zone diameter breakpoints can reliably identify resistant strains in a routine laboratory setting.
• This method aids in the early detection of concerning Clostridium difficile strains like PCR ribotype 027.