DETECTION OF EXTENDED SPECTRUM βLACTAMASES IN SHIGA TOXIN PRODUCING ESCHERICHIA COLI ISOLATED FROM DIFFERENT RAW MEAT SAMPLES
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Date
2018-10
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SRI VENKATESWARA VETERINARY UNIVERSITY TIRUPATI - 517502. (A.P.) INDIA
Abstract
Shiga toxin producing Escherichia coli is an important foodborne pathogen having worldwide public health concern. The present study was undertaken to characterize STEC from raw meats of animal origin and human origin based on cultural and biochemical isolation, PCR detection, virulence profiles, antibiogram, serotyping and genetic diversity. A total of 523 samples comprising raw foods of animal origin (470) and human diarrhoeic stools (53) were examined. Out of 523 total samples collected, 178 (34.03%) samples were positive for Escherichia coli by cultural and molecular methods. Out of 178 E. coli isolates, 154/470 (32.76%) isolates were from raw foods of animal origin and 24/53 (45.28%) from human diarrhoeic stool samples.Out of 470 food samples screened,the highest rate of E. coli isolation was recorded from mutton (47.27%, 26/55), followed by cara beef (33.33%, 13/39) and chicken (30.58%, 115/376). Out of a total of 178 E. coli isolates, m-PCR revealed 43 (24.1%) isolates as STEC. Among the 43 STEC isolates, 9 (34.6%) were from mutton samples, 6 (46.1%) cara beef samples, 19 (16.5%) chicken samples and 9 (37.5%) human isolates. The genes stx1, stx2, eaeA and hlyAwere detected in 93.02%, 39.53%, 44.18% and 46.51% of STEC isolates, respectively. Two mutton samples showed all the four targeted genes in present study. Antibiogram study of STEC isolates revealed sensitivity towards fosfomycin (100%) chloramphenicol (95.3%), gentamicin (55.8%) and Amikacin (53.4%). Higher resistance was observed for vancomycin (100%), erythromycin (100%), streptomycin (100%), ciprofloxacin (95.3%), naladixic acid (93%), Ampicillin (90.6%), cefotaxime (86%), ceftazidime (81.3%), ceftriaxone (74.1%) and co-trimoxazole (58.1%). Notable percentages of isolates were intermediately resistant against norfloxacin (32.5%), kanamycin and tetracycline (27.9% each)and aztreonam (16.2%). ESBL phenotypes were confirmed in a total of 21 STEC isolates using phenotypic confirmation tests. β-lactamase genes were detected in a total of 21(48.8%) STEC isolates, with blaTEM being the predominant gene detected (25.5%, 11/43) followed by blaCTX-M group I (20.9%, 9/43), blaOXA(13.9%, 6/43), blaSHV(9.3%, 4/43), blaCTX-M group II ( 4.6%, 2/43) and no single isolate showed blaAmpCgene among all the tested STEC isolates. Prevalence rates of βlactamase genes among different samples is 57.8%, 44.4%, 50% and 33.3% among the STEC isolates obtained from raw meat of chicken, mutton, cara beef and human diarrhoeic stool samples, respectively. CTX-M beta-lactamase was found to be the most frequent mechanism of ESBL resistance in STEC isolates of the present study. All the 21 ESBL producing STEC isolates were sent for serotyping on the basis of ‘O’ antigen and 9 of them were belonging to serotype O22, 4 were serotype O88 and others were ONT. ERIC PCR and REP-PCR analysis revealed a greater degree of heterogeneity among STEC isolates from different and within the same sources. Of the 21 ESBL producing STECisolates analyzed, 21 ERIC-PCR patterns and 21 REP-PCR patterns were obtained by using ERIC and REP-PCR analysis, respectively. The discriminatory power for both ERIC and REP-PCR was found to be 0.999. Genetic diversity of STEC recovered from foods of animal origin and humans in India adds to the heterogeneity reports among STECspecies world-wide, supporting diversity among same species. Close clustering between STECfrom raw meats of animal origin and human origin is apossible indicative of probable cross contamination and its zoonotic significance.
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