Antimicrobial resistant Shigella in North India since the turn of the 21st century

Purpose: The ubiquitous presence and rampant spread of antibiotic resistant strains of Shigella spp is a major public health concern. Therefore, monitoring the trends of antimicrobial resistance in them is essential. Methods: A total of 15440 stool samples were inoculated on MacConkey agar, lysine deoxycholate agar and Selenite F enrichment broth from 2001 to 2015.Out of 491 shigellae isolated, 250 isolates were recovered from our culture collection. Antimicrobial susceptibility was performed by Kirby Bauer disc diffusion method, E-test and phenotypic resistance screening for ESBL and AmpC production was performed. For the detection of beta-lactamase genes, PCR for blaSHV, blaOXA, blaCTX-M-15, CMY-2 and mphA PCR in isolates with decreased susceptibility to azithromycin(DSA) was performed. Results: S. flexneri (n = 173) was most common, followed by S.dysenteriae (n = 24), S.sonnei (n = 23), S.boydii (n = 10) and Non agglutinating Shigella (NAG, n = 20). A see-saw pattern in the prevalence of S. flexneri and S. dysenteriae and rising prevalence of S. sonnei and NAG was seen. Majority (77%) of the isolates had MICs >4 mg/L for ciprofloxacin and >50% had high MIC90 (12 mg/L) for ceftriaxone and cefepime (8 mg/L). Nearly 20% of S.flexneri were resistant to third generation cephalosporin by disc diffusion and 33.7% had MIC >= 1 mu g/mL. Among the ceftriaxone resistant isolates (n = 29) the blaTEM beta-lactamase resistance gene was seen in all, blaCTX-M-15 in 37%, blaCMY-2 in 45.6% and blaOXA in 52%. The first report of DSA at our institute was in 2001 (n = 1, 2.5%) which increased to 35.1% (n = 40) in 2011-15. The isolates with DSA included S. flexneri (n = 40), S. boydii (n = 4) and S. sonnei (n = 1) and plasmid mediated resistance to azithromycin by mphA gene was detected in 19 out of 40 isolates of S. flexneri. Conclusion: Global emergence of resistance Shigella is a matter of concern and calls for systematic monitoring and periodic updates of countrywide and local antibiogram.