Antimicrobial susceptibility profile, treatment outcome and serotype distribution of clinical isolates of Salmonella enterica subspecies enterica: a 2-year study from Kerala, South India

Abstract

Background/purpose: Typhoid and paratyphoid fever continue to be important causes of illness and death in parts of Asia, being associated with poor sanitation and consumption of unsafe food and water. Antimicrobial resistance has emerged to traditional first-line drugs, namely, the fluoroquinolones, as well as to third-generation cephalosporins, posing challenges to treatment. Azithromycin has proven to be an effective alternative for treatment of uncomplicated typhoid fever. The purpose of this study was to determine the antimicrobial susceptibility, clinical outcome and serotype distribution pattern of clinical isolates belonging to Salmonella enterica subspecies enterica.

Methodology: All clinical isolates of S. enterica obtained from blood, sterile body fluids, as well as stool and urine samples at Amrita Institute of Medical Sciences and Research Centre, Kerala, India, between August 2011 and July 2013 were included in the study and processed based on standard microbiology protocols.

Results: A total of 118 isolates of Salmonella were obtained during the study period. Out of these, 79 were of S. Typhi (66.95%), followed by isolates of S. Paratyphi A (22; 18.64%) and S. Typhimurium 12 (10.17%). Five isolates could not be identified further. There was 100% susceptibility to ceftriaxone in all S. enterica subspecies. Ciprofloxacin susceptibility was 32.91% for S. Typhi and 40.90% for S. Paratyphi A as determined by the disk diffusion method. The susceptibility profile of S. Typhi isolates to different antimicrobials was as follows: chloramphenicol (94.93%), ampicillin (77.21%), cotrimoxazole (75.94%) and azithromycin (78.48%). For S. Typhi, the minimum inhibitory concentration (MIC) of ciprofloxacin required to inhibit the growth of 50% of organisms was 0.5 μg/mL (intermediate) and MIC required to inhibit the growth of 90% of organisms was 1 μg/mL (resistant). S. Typhimurium was 100% susceptible to cotrimoxazole, ampicillin, ceftriaxone, chloramphenicol, ofloxacin and azithromycin. Susceptibility to ciprofloxacin was 66.66%. Patients from whom S. Typhimurium was isolated had comorbidities with documented risk. Of the 118 patients, 3 expired. Two had typhoid fever and were in sepsis at admission. One had S. Typhimurium and was suffering from multiple myeloma.

Conclusion: S. Typhi was the predominant isolate. All isolates were susceptible to ceftriaxone. Chloramphenicol susceptibility was >90%. No multidrug-resistant Salmonella strains were isolated. Susceptibility to ciprofloxacin for S. Typhi was 33%. Recovery rate was 97%.

Keywords: Salmonella enterica; clinical isolates; susceptibility profile.