Characterization of Coliform Bacteria Isolated From Surface Water

The present study was undertaken to assess the phenotypic and genotypic characteristics of total coliforms bacteria. The work involved in isolation, identification and characterization of the coliform bacteria e.g. Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae and Citrobacter freundii from surface waters in and around Dhaka, Bangladesh. Among the 278 environmental isolates, 48 were Escherichia coli, 19 Klebsiella pneumoniae, 18 Enterobacter cloacae and 37 Citrobacter freundii which were primarily identified by cultural, biochemical and analytical profile index test (API) tests. Escherichia coli were further confirmed by using the fluorescence agent, 4-methylumbelliferyl-β-D-glucuronide (MUG). At 37oC, 84% E. coli gave positive result for MUG whereas only 46% E. coli were MUG positive at 44.5oC. Only 16% K. pneumoniae was MUG positive at 37oC and E. cloacae and C. freundii could not grow on MUG medium. In this study, Ceftazidime, Aztreonam, Cefixime and Amoxycillin/Clavulanic acid (2:1) antibiotics were used to assess extended spectrum β- lactamase producing bacteria. Total 86% of the coliform showed positive result for ESBL. In this study, sixteen different antibiotics were used for observation of drug resistance pattern by disk diffusion method. Most of the strains were resistant to penicillin, oxacillin, erythromycin, bacitracin respectively and the lowest resistance was against imipenam. Correlation with the tolerance/susceptibility of antibiotics and the plasmid profile of coliforms was studied. Based on the result, the most resistant isolate was identified as Klebsiella pneumoniae and its plasmid size was 20.92 KB. Congo red binding test was also performed to differentiate between virulent and avirulent E. coli. Within coliform, 27% and 11% of E. coli and Klebsiella sp. gave positive result for congo red binding assay respectively. The finding of this study revealed that drug resistance and other virulence properties potential of the members of the coliforms was observed in many isolates that reflects an alarming signal for water quality. It also presents a scenario of the acquiring of virulence properties and drug resistance to a group of bacteria that are considered to be avirulent commensals to human.