Drug Resistance Pattern in the Recent Isolates of Salmonella Typhi with Special Reference to Cephalosporins and Azithromycin in the Gangetic Plain.

INTRODUCTION: Typhoid fever is an endemic disease in India against which many antibiotics are available. In the recent times, emerging resistance to traditional antibiotics, such as Ampicillin, Chloramphenicol and Trimethoprim/sulfamethoxazole, Azithro-mycin and third generation Cephalosporins are being reported and increasingly being used in the treatment of invasive Salmonella infections. However, the latter two drugs have been reported with occasional clinical failures. Currently, we do not have data regarding their drug resistance levels in the recent isolates of Salmonella enterica subspecies enterica serotype Typhi.

AIM: To determine the current levels of drug resistance of the two drugs (i.e., cephalosporins and azithromycin) against S. Typhi isolates.

MATERIALS AND METHODS: It is a prospective case study. A total of 47 recent strains of S. Typhi were isolated from blood and stool specimens. These isolates were subjected to identification and confirmation by biochemical, serological tests followed by genotypic methods. The antimicrobial testing was done by disc diffusion and Minimum Inhibitory Concentration (MIC) methods for various in use antibiotics including ceftriaxone and azithromycin from February 2011 to March 2013 in the Department of Microbiology, Institute of Medical Sciences, Banaras Hindu University, Varanasi, India.

RESULTS: It was intriguing to see the return of conventional drugs such as chloramphenicol, amoxicillin and co-trimoxazole. The drugs like quinolones, ceftriaxone and azithromycin were found to be ineffective against >20% of the isolates. However, nalidixic acid was found to have maximum resistance (36/47,76.6%) while highest sensitivity was observed for chloramphenicol (1/47,2.1%). Moreover, co-trimoxazole (9/47,19.1%) has displayed with significant come back.

CONCLUSION: It could be concluded that combination of amoxicillin and co-trimoxazole would prove as good as azithromycin or ceftriaxone alone for empirical therapy of S. Typhi infection. However, detection of an isolate (1/47, 2.1%), sensitive only to chloramphenicol, a drug known for causing bone marrow suppression, is an alarming sign.