Drug resistant Shigella flexneri in & around Dibrugarh, north-east India

Background & objectives: Shigella flexneri is the most common species of Shigella causing diarrhoea and dysentery in Asia including India. Multidrug resistance in Shigella species has been reported worldwide and there is rising concern regarding development of fluoroquinolone resistance. This study was undertaken to find out the resistance pattern of Sh. flexneri, the commonest shigella isolated in Dibrugarh, north east India, including detection of fluoroquinolone resistance and extended spectrum beta lactamases. Methods: Stool samples collected from patients of diarrhoea and dysentery were tested for bacterial enteropathogens. Strains of Shigella species were confirmed by biochemical tests. Speciation was done using commercially available polyvalent antiserum. Antimicrobial susceptibility test was performed by Kirby Bauer disc diffusion method against 18 different antibiotics. Extended spectrum beta lactamase (ESBL) detection was done by disc approximation test as well as combination disc method and minimum inhibitory concentrations (MIC) of different antibiotics were also measured. Results: Multidrug resistance in Sh. flexneri was found to be common (90.2%) and the commonest phenotypic multi-drug resistance profile was ampicillin-tetracycline-co-trimoxazole-nalidixic acid. High resistance to nalidixic acid was detected in 90.3 per cent isolates (MIC >240 mu g/ml) and ciprofloxacin resistance was seen emerging in this region (11.2%, MIC >4 mu g/ml). Present of ESBL was phenotypically confirmed in two cases. Besides the fluoroquinolones, chloramphenicol, piperacillin-tazobactum and the third generation cephalosporins were effective in 87-100 per cent of the isolates. Interpretation & conclusions: Our study showed high resistance (MIC >240 mu g/ml) against nalidixic acid in Sh. flexneri isolates. Ciprofloxacin resistance is also emerging in this region. Shigellosis due to ESBL carrying Shigella can become a serious threat to public health. Guidelines for therapy should be monitored and modified based on regional reports of resistance to antimicrobial agents.