Multidrug Resistance in Large-Plasmid-Associated Presumptive Enterohaemorrhagic Escherichia coli Isolated from Contaminated Lake Water

Abstract

To determine the presence of enterohaemorrhagic Escherichia coli (EHEC), 50 water samples of three different lakes in Dhaka, Bangladesh were studied. A total of 90 strains were examined thoroughly to isolate sorbitol non-fermenting (NSF) E. coli. Twelve of 90 isolates (13.3%) from 5 samples were found to be sorbitol nonfermenter, which were further screened for rhamnose, cellobiose and sucrose fermentation. Eleven (12.2%) of 90 isolates also tested negative for cellobiose and sucrose fermentation, while only 3 (3.3%) of them were found to be rhamnose non-fermenting. Biochemical tests confirmed that 91.7% (11 of 12) of NSF strains were indole positive. Eleven NSF E. coli isolates survived at 45.5°C and mostly produced gas by fermentation within 24h. After antimicrobial susceptibility testing, 91.7% (n=11) of these isolates were found resistant to cephalexin, ampicillin and amoxicillin. Ceftazidime and nalidixic acid resistance was also observed in 75% (9 of 12) and 58.3% (7 of 12) isolates, respectively. Plasmid profile analysis revealed that nine (75%) strains harboured large plasmids of >35.8-140 megadaltons (MDa), four (33.3%) of which contained 60-MDa plasmid. Also, the large-plasmid-associated strains shared common behaviour in antimicrobial resistance and eight (88.9%) of these were resistant to four or more antibiotics. Our data suggest a possible association of source water contamination in Bangladesh with multidrug-resistant (MDR) EHEC, which is alarming to public health. DOI: http://dx.doi.org/10.3329/bjm.v28i1.11807 Bangladesh J Microbiol, Volume 28, Number 1, June 2011, pp 33-40