Hastyar H. Najmuldeen
Aims: This study was designed to determine the extent of contamination of water storage tanks by non-lactose fermenter Enterobacter spp, and to characterize the chlorine and antibiotic resistance status. Finally, to find the correlation between biofilm formation and resistance to chlorine. Methods: A total of 60 water samples were collected from residential and restaurant water storage tanks. Bacterial analysis and antibiotic susceptibility profiles of the samples were assessed by the most probable number (MPN) and Vitek 2 compact tests, respectively. The biofilm formation was quantified by crystal violet staining method and chlorine resistance test by microdilution technique. Results: More coliform group contamination was recorded in residential- 40% than the restaurant water tanks 30%. Further evaluation of the samples assessed to be negative by the MPN test showed that 44% of home- and 43% of restaurant water samples were positive for Enterobacter cloacae. Further analysis of these isolates revealed that they displayed variation in resistance to different concentrations of chlorine, and similar antibiotic susceptibility profiles. Biofilm analysis showed no difference in biofilm formation, except the isolates that were resistant to concentration of chlorine, 400 mg L-1, formed significantly more biofilm than those that were resistant to other concentrations. A moderate positive non-linear correlation (r = 0.72) was found between the degree of biofilm formation and the ability of isolates to resist different chlorine concentrations (p<0.05), and no correlation has been detected between antibiotic and chlorine resistance. Conclusions: The presence of E. cloacae in drinking water suggests a public health concern. The routine microbial water analysis should be modified to include detection of non-lactose fermenter Enterobacter. Impact of Study: The presence of chlorine resistant, non-lactose fermenter Enterobacter spp in drinking water can pose a real public health threat. Therefore, the water samples should be routinely tested for the presence of Enterobacter spp.
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