Culture-Dependent and Culture-Independent Methods in Evaluation of Emission of Enterobacteriaceae from Sewage to the Air and Surface Water

Abstract

The number of Enterobacteriaceae, with particular attention given to the presence of Escherichia coli and Klebsiella pneumoniae, was determined in hospital effluents and municipal wastewater after various stages of purification. The emission of these microorganisms to the ambient air near wastewater treatment plant (WWTP) facilities and to the river water, which is a receiver of the WWTP effluent, was also studied using fluorescence in situ hybridization (FISH) and cultivation methods. The number of Enterobacteriaceae determined by cultivation and fluorescence methods in different kinds of sewage sample ranged from 0.5 × 103 to 2.9 × 106 CFU/ml and from 2.2 × 105 to 1.3 × 108 cells/ml, respectively. Their removal rates during treatment processes were close to 99 %, but the number of these bacteria in the WWTP outflow was quite high and ranged from 5.9 × 103 to 3.5 × 104 CFU/ml and from 1.1 × 105 to 6.1 × 105 cells/ml, respectively. In the river water and the air samples, the number of Enterobacteriaceae was also high and ranged from 4.1 × 103 to 7.9 × 103 CFU/ml and from 3 to 458 CFU/m3, respectively. The numbers of these microorganisms obtained from fluorescence and cultivation methods were statistically and significantly correlated; however, the analysis of the studied samples indicated that the FISH method gave values up to 103-fold times greater than those obtained by the cultivation method. From a sanitary point of view, this means that the number of viable fecal bacteria is systematically underestimated by traditional culture-based methods. Thus, the FISH proves to be a method that could be used to estimate bacterial load, particularly in air samples and less contaminated river water.