Azithromycin Resistance in Clinical Isolates of Salmonella enterica Serovars Typhi and Paratyphi in Bangladesh

Objective: Salmonella enterica serovars Typhi and Paratyphi, the causative agents of typhoid and paratyphoid, are major threats in developing countries. The present study aimed to investigate the resistance pattern of 40 clinically isolated Salmonella enterica serovars Typhi (n = 33) and Paratyphi (n = 7) to commonly used antibiotics, particularly azithromycin. Materials and Methods: The disc diffusion method was used to investigate the resistance pattern of the clinical isolates against selected antibiotics. Minimum inhibitory concentration (MIC) was determined by the broth dilution method. Plate-based assays were used for the detection of efflux pumps. Results: It was observed that 95% of the test isolates were resistant to azithromycin and 100% were resistant to clindamycin. MIC values of azithromycin ranged between 32 and 128 mu g mL(-1). Although 90% of isolates contained efflux pump, none of the isolates was found to have the mef(A) gene, indicating that some other efflux pump(s) might be present. Macrolide resistance gene, erm(B), was present in 25 isolates (62.5%). Other resistance genes were absent. Plasmids were absent, but class 1 integrons were present in 80% of the isolates. Conclusions: The occurrence of macrolide resistance in clinical Salmonella enterica serovars Typhi and Paratyphi is of particular significance in Bangladesh where azithromycin is a commonly used drug against most diseases.