Rapid emergence of third-generation cephalosporin resistance in Shigella sp. isolated in Andaman and Nicobar Islands, India.

Shigellosis is a major cause of diarrheal diseases among children in Andaman & Nicobar Islands, India, which have a population of 350,000 people, including settlers from mainland India and 6 indigenous tribes. From the last one-and-half decade, we have been monitoring the species distribution and emergence of antibiotic resistance among the isolates of Shigella. The circulating Shigella strains have been found rapidly acquiring resistance to a wide spectrum of antibiotics. The recent data indicate that a significant proportion of Shigella isolates have been resistant to newer generation of cephalosporins, which are used as an alternative of quinolones to treat the patients with shigellosis. In this communication, we report the antibiotic-resistant pattern of Shigella isolates that are recently isolated from these islands. From January 2008 to December 2009, 311 stool samples were processed and 44 (14%) Shigella isolates were recovered. Out of these 44 Shigella isolates, 6 (14%) were found to be resistant to all the three third-generation cephalosporins tested. The minimum inhibitory concentrations of the resistant isolates were all above the breakpoint for reduced susceptibility as per the Clinical and Laboratory Standards Institute guidelines. All of the cephalosporin-resistant Shigella strains were confirmed to produce extended-spectrum ß-lactamases. By analyzing trends in the resistance patterns of the various Shigella species, we found that Shigella dysenteriae (40%) is currently more resistant, followed by Shigella flexneri (14%), than the other Shigella species in these islands of India, especially to the third-generation cephalosporins. The acquisition of resistance by enteric pathogens to the increasing number of antibacterial drugs is becoming a grave concern, particularly in developing countries where shigellosis is of a common occurrence.