Antimicrobial Resistance in Salmonella Experience of an Infectious Diseases Hospital in Mumbai, India

Background: Enteric fever (EF) remains an important public health problem, particularly in the developing countries. The last two decades have witnessed the emergence of multidrug- resistant (MDR) salmonella strains.Objectives: To detect antimicrobial resistance among salmonella isolates from EF cases and to determine the minimum inhibitory concentration (MIC) of ciprofloxacin in nalidixic acid (NA) sensitive/ resistant strains of salmonellae.

Material and Methods: 890 clinically suspected cases of EF were studied at an Infectious diseases hospital in Mumbai between January June 2006. Clot culture was done in bile broth using conventional techniques. Typical nonlactose fermenting colonies on MacConkey agar were selected and identified by Gram's stain and conventional biochemical tests. Salmonella species were further confirmed by slide agglutination test using polyvalent and factor sera (Denka seiken, Japan). Antimicrobial susceptibility testing was done by Kirby-Bauer disk diffusion method in accordance with the CLSI guidelines and interpretative criteria.

Results: Fifty salmonella isolates from 890 suspected cases of EF (5.6%), comprised of Salmonella typhi (28;56%) and Salmonella paratyphi A (22;44%). All the isolates were sensitive to ciprofloxacin. The 49 (98%) NA-resistant strains had raised MIC of ciprofloxacin. Analysis of 5-year data revealed increasing resistance to NA, increasing sensitivity to chloramphenicol with ciprofloxacin sensitivity constant at 100%.

Conclusions: Recognition of a distinct subset of EF salmonellae having low-level resistance to ciprofloxacin is important for proper patient management in these cases. Vigilance for the emergence of ciprofloxacin or ceftriaxone-resistant strains is recommended.