Species Diversity and Changing Patterns of Antimicrobial Susceptibility of Shigella Serotypes Isolated from Stool Samples in a Tertiary Health Care Hospital of Punjab, North India, a 5 Year Study

Shigella is an important cause of invasive dysentery in children and others. The present study was done to study the prevalence, any seasonal variation, distribution among children and adults, and antimicrobial susceptibility pattern of Shigella isolates in stools. A retrospective study was conducted over a period of 5 year from 1 January 2009 to 31th December 2013 in the department of microbiology, in a tertiary care hospital in Punjab. Stool specimens from diarrhea/dysentery cases in different age-groups were processed. The specimens were processed by standard microbiological techniques. The suspected colonies of Shigella were identified by standard biochemical tests and serotyping was done by group specific antisera. The susceptibility of all the isolated Shigella species to different antibiotics were done by KirbyBauer’s disk diffusion technique as per the Clinical and Laboratory Standards Institute (CLSI) guidelines. Shigella species were isolated from 146 (2.42%) of the total 6025 stool samples received during the study period. Among these, S.flexneri was the predominant species accounting for 67.1% of isolates, followed by S.sonnei 25.3%, S.boydii 5.4% and S. dysenteriae in 2.1% of the total number of isolates. Of these, 53% were from children from 0-18 years and the rest 47% were from adults. Over 70% of Shigella isolates were resistant to two or more drugs including ampicillin, and co-trimoxazole and approximately, 3% Shigella isolates were resistant to ceftriaxone, during the study period. Analysis of the antibiotic susceptibility data showed a gradual increase in resistance to ampicillin, fluctuating resistance to norfloxacin and persistent resistance to co-trimoxazole. No resistance was observed to cefoperazone/sulbactam, piperacillin/tazobactam, and imipenem during the study period. The results of the study revealed the high prevalence of shigellosis with S. flexneri as the predominant species. The result also suggests that ampicillin, co-trimoxazole and norfloxacin should not be used empirically as the first line drugs in the treatment of shigellosis. Periodic analysis and reporting of antibiotic susceptibility is an important measure to check for antibiotic resistance and form appropriate treatment protocols.