Antimicrobial Resistance Pattern of Shigella species Over Five Years at a Tertiary-care Teaching Hospital in North India

Sir, Shigellosis is a global human health problem, especially in developing countries where there are inadequate hygiene and unsafe water supplies (1,2). Shigella accounts for a significant proportion of cases of bacillary dysentery in many tropical and subtropical countries (3,4). Shigella is one of the most important causes of gastroenteritis-induced deaths in 3-5 million children aged less than five years in developing countries (5). The emergence of multiple drug resistance to cost-effective antimicrobials against Shigella is a matter of concern in developing countries (6). It is also well-documented that pandemic strains often exhibit multiple antimicrobial resistance and induce severe illness with high case fatality in all age-groups (7). In the tropics, most infections occur due to S. flexneri and infections that occur primarily due to Shigella sonnei are less common (8,9). Over a decade ago, results of active surveillance studies showed that, in most endemic countries, especially in Asia and sub-Saharan Africa, there was an emergence of multidrug resistance to different antimicrobials, including ampicillin, co-trimoxazole, and nalidixic acid (9). Besides the temporal changes in the antibiogram of Shigella species, it is well-known that antimicrobial susceptibility patterns in Shigella may differ between geographical areas. Such differences are never stable and may change rapidly, especially in places where antimicrobials are used excessively, particularly in developing countries (1). This warrants for robust monitoring of the pattern of antibiogram for this organism. Hence, the present study was conducted to determine the incidence and prevalence of Shigella serogroups isolated from cases of dysentery during a five-year period from 2004 to 2008 and also to determine the drug resistance pattern of Shigella in a tertiary-care hospital in North India. In this cross-sectional study, patients presenting with acute, bloody diarrhoea, suggestive of shigellosis, during 2004-2008, were included. Stool samples were collected from all patients presenting with symptoms of diarrhoea, blood or mucus in stool, fever, and abdominal pain. In total, 12,983 stool samples were received for culture and routine microscopy during 2004-2008. All the samples were subjected to routine microscopy and were examined for pus cells, trophozoites, and cysts. Only those samples which showed pus cells and/or red blood cells were cultured. The stool specimens from such symptomatic patients were cultured on differential and selective media, including MacConkey agar, Xylose-lysine desoxycholate agar, and deoxycholate citrate agar as primary plates. Loop-full sample was also inoculated into selenite-F broth. The plates were incubated at 37 [degrees]C for 24 hours. Suspected colonies on solid plates, which were Gram-negative upon Gram-staining and oxidase test-negative, were biochemically characterized as per standard procedures. Presumptive Shigella isolates on Triple Sugar Iron agar were serotyped by slide agglutination tests with Shigella polyvalent grouping and monovalent antisera (Denka Seiken Co. Ltd., Tokyo, Japan). Antimicrobial susceptibility testing and resistance patterns of the Shigella isolates to various antimicrobials were determined by the disc-diffusion technique (10). Every inoculum was prepared by inoculating 5 mL of Mueller-Hinton broth with five colonies of an 18-hour old pure Shigella culture, followed by incubation in ambient air and at 37 [degrees]C for 16 hours. Turbidity of the broth was equilibrated to match with 0.5 McFarland standards. A sterile cotton swab was dipped into the standardized suspension, drained, and used for inoculating 25 mL of Mueller-Hinton agar in a 90-mm plate. The inoculating plates were air-dried, and antimicrobial discs, included ampicillin (10 [micro]g), chloramphenicol (30 [micro]g), co-trimoxazole (25 [micro]g), tetracycline (30 [micro]g), gentamicin (10 [micro]g), nalidixic acid (30 [micro]g), and ciprofloxacin (5 [micro]g). …