Shifting serotypes, plasmid profile analysis and antimicrobial resistance pattern of shigellae strains isolated from Kolkata, India during 1995-2000.

One hundred and sixty-six shigellae strains, isolated from stool samples of paediatric patients (< 5 years old) at a Childrens' Hospital in Kolkata, India during the period of 1995-2000 were examined for serotyping, drug resistance pattern and plasmid profiles. Sh. flexneri (58 %) was found to be commonest isolate of total shigellae, followed by Sh. sonnei (28 %), Sh. boydii (9%) and Sh. dysenteriae (5%). This profile of species was in sharp contrast to the picture obtained before 1995, when Sh. dysenteriae 1 predominated over Sh. flexneri. In Sh. flexneri strains, Sh. flexneri 2a (35%) was the most prevalent serotype, following Sh. flexneri 3a (31%), Sh. flexneri 6 (14%), Sh. flexneri 2b (11%) and Sh. flexneri 4 (9%). Resistance patterns of the strains to 12 commonly used antimicrobial agents and minimum inhibitory concentrations (MICs) of the antibiotics were also tested. All strains were found uniformly susceptible to norfloxacin, but more than 90% strains were resistant to tetracycline, co-trimoxazole and 67% strains were resistant to ampicillin. Resistance to amoxicillin, chloramphenicol and nalidixic acid was found in 55% (range 45-74%), 46% (range 40-60%) and 29% (range 15-40%) strains respectively. Overall, shigellae strains showed statistically significant increase in resistance against tetracycline, nalidixic acid and furazolidone (P < 0.05) over the years of this study. This indicates decreased efficacy of furazolidone, cotrimoxazole and nalidixic acid for the empirical treatment of shigellosis in Kolkata. Although a few strains showed intermediate susceptibility to ciprofloxacin (4%) and cefotaxime (10%) by disk diffusion test, but the MICs of those antibiotics were within the normal limits. Almost 57% of the strains were resistant to four or more drugs with high MICs of the antibiotics. Plasmid profile analysis revealed presence of large plasmid of 220 kb in majority of the strains except in Sh. sonnei and a correlation between presence of smaller plasmids and shigellae serotypes. Hence this study reports epidemiological change of shigellae species in Kolkata, India with regard to serotypes and antibiotic resistance patterns.