Gram negative anaerobe susceptibility testing in clinical isolates using Sensititre and Etest methods

Area of Science:

• Clinical Microbiology
• Infectious Diseases
• Antimicrobial Resistance

Background:

• Gram-negative anaerobic bacteria are significant pathogens in various infections.
• Antimicrobial susceptibility testing for these organisms is not routinely performed.
• Accurate identification and susceptibility data are vital for effective treatment.

Purpose of the Study:

• To evaluate anaerobic susceptibility testing methods for Gram-negative anaerobes.
• To assess the susceptibility patterns of clinical isolates to key antibiotics.
• To compare the performance of Sensititre and Etest methods.

Main Methods:

• 70 Gram-negative anaerobic isolates identified via MALDI-TOF MS.
• Susceptibility testing using Sensititre trays (15 antibiotics) and Etests (5 antibiotics).
• Comparison of Sensititre and Etest methods against a gold standard.

Main Results:

• All isolates were susceptible to metronidazole.
• High susceptibility rates observed for piperacillin-tazobactam (93-100%) and amoxicillin-clavulanate (89-100%).
• Two Bacteroides fragilis isolates showed resistance to broad-spectrum β-lactams and carbapenems; high agreement between testing methods (92-100%).

Conclusions:

• Metronidazole is an appropriate broad-spectrum anti-anaerobic agent in this region.
• Anaerobic susceptibility testing is recommended for clinical isolates, especially from sterile sites.
• Emerging resistance in Bacteroides fragilis warrants monitoring; Etest method preferred for its advantages.