Decreased susceptibility to antimicrobials among Shigella flexneri isolates in Manipal, South India - A 5 year hospital based study

Shigellosis is endemic in many developing countries and an important cause of bloody diarrhea worldwide. Our study was undertaken as a continuation of our earlier study during 2001-2006. The aim of this study was to monitor changes in Shigella serogroups and resistance patterns to antimicrobials among Shigella isolates. Two thousand one hundred fecal samples were obtained from patients with diarrhea during June 2006 - June 2011. Isolates were identified by standard microbiological techniques as Shigella spp and the disk diffusion method was used to determine antimicrobial susceptibility following CLSI guidelines. Of the 2,100 fecal samples, 77 (3.7%) contained Shigella spp, of which 73 (94.8%) were S.flexneri, 3 (3.9%) were S. sonnei and 1 (1.3%) was S. dysentriae type 1. S. boydii was not identified. One hundred percent resistance was noted against nalidixic acid. There were high levels of resistance to other antimicrobials: ampicillin (100%), Co-trimoxazole (89.6%), tetracycline (84.4%), ciprofloxacin (87%) and norfloxacin (83.1%). Most of the isolates were susceptible to ceftriaxone except for 2 isolates of S. flexneri. Antibiotic treatment of shigellosis is needed to prevent mortality. Increasing fluoroquinolone resistance leaves us dependent on third generation cephalosporins for treating shigellosis. Emerging resistance to these cephalosporins was seen in our study.