Disk diffusion susceptibility testing of Nocardia species

Area of Science:

• Microbiology
• Infectious Diseases
• Pharmacology

Background:

• Nocardia infections pose a significant clinical challenge.
• Accurate antimicrobial susceptibility testing is crucial for effective treatment of Nocardia infections.

Purpose of the Study:

• To determine the in vitro effectiveness of 13 antimicrobial agents against clinical isolates of Nocardia.
• To compare agar dilution and disk diffusion methods for Nocardia susceptibility testing.

Main Methods:

• Agar dilution and disk diffusion methods were employed.
• Fifty-one clinical isolates of Nocardia were tested against 13 antimicrobial agents.
• Minimal inhibitory concentrations (MICs) and zone diameters of inhibition were recorded.

Main Results:

• Sulfisoxazole and trimethoprim-sulfamethoxazole demonstrated high activity against Nocardia isolates.
• Amikacin and other aminoglycosides showed good correlation between MICs and zone diameters.
• Minocycline inhibited all isolates, but susceptibility determination by zone diameter was not feasible.
• Variability was observed with sulfa disks, yet they distinguished sensitive from intermediate strains.
• Growth rate limitations affected susceptibility testing for approximately one-third of Nocardia isolates.

Conclusions:

• Trimethoprim-sulfamethoxazole and sulfisoxazole are promising agents for Nocardia treatment.
• Standardized susceptibility testing methods are needed for Nocardia, considering inoculum effects and growth rates.
• Further research is warranted to optimize antimicrobial susceptibility testing for Nocardia.