Transferable trimethoprim resistance of shigellae encountered in Vellore (south India)

Area of Science:

• Microbiology
• Infectious Diseases
• Antimicrobial Resistance

Background:

• Shigella species are significant causes of bacterial dysentery worldwide.
• Antimicrobial resistance in Shigella poses a major public health challenge, particularly in developing regions.
• Trimethoprim and trimethoprim-sulfamethoxazole are commonly used antibiotics for treating Shigella infections.

Purpose of the Study:

• To investigate the prevalence and mechanisms of trimethoprim and trimethoprim-sulfamethoxazole resistance in Shigella flexneri and Shigella shigae strains.
• To determine if high-level resistance observed in these strains is transferable and plasmid-mediated.

Main Methods:

• Clinical isolates of Shigella flexneri and Shigella shigae from Vellore, South India were screened for antibiotic susceptibility.
• Minimum Inhibitory Concentrations (MICs) were determined for trimethoprim and trimethoprim-sulfamethoxazole.
• Plasmid transfer experiments (conjugation) were performed using resistant strains as donors and susceptible strains as recipients.

Main Results:

• A high prevalence of resistance to trimethoprim and trimethoprim-sulfamethoxazole was observed in the studied Shigella strains.
• Eighty-four percent of the resistant isolates exhibited high-level resistance.
• Plasmid transfer studies confirmed that high-level trimethoprim resistance is transferable, indicating a plasmid-mediated mechanism.

Conclusions:

• Shigella flexneri and Shigella shigae in Vellore exhibit significant high-level resistance to trimethoprim and trimethoprim-sulfamethoxazole.
• The resistance is largely plasmid-mediated, suggesting potential for further dissemination.
• These findings highlight the urgent need for monitoring and alternative therapeutic strategies against Shigella infections in the region.