Isolation and characterization of coliphages from different water sources and their biocontrol application combined with electron beam irradiation for elimination of E. coli in domestic wastewater

Abstract

Antibiotic-resistant bacteria, including Escherichia coli (E. coli), are high-risk waterborne pathogens that pose a vital threat to the general public’s health. Therefore, this study aims to develop alternative and affordable treatment approaches. Coliphage treatment is an economically and environmentally sustainable method for eliminating pathogenic bacteria. A significant step toward improving germicidal effectiveness might be to combine coliphage with electron beam treatment. Twelve isolated E. coli were used as host bacteria. In addition, eleven coliphages were isolated and characterized to determine their suitable host range and lytic activities. Antibiotic resistance was tested to detect the most antimicrobial-resistant E. coli isolates. Results indicated that E. coli-2 and E. coli-10 were the most resistant bacterial isolates. Both somatic coliphage-3 (S3) and F-specific coliphage-3 (F3) were the most active lytic coliphages. Based on transmission electron microscope analysis, S3 was classified as a member of the Myoviridae family, while F3 belonged to the Leviviridae family. Genome types were detected; the S3 genome was a linear double-stranded DNA virus, while the F3 genome was a single-strand RNA virus. The adjustment of pH to 7 and temperature to 38 °C increased coliphage activity by 32.2% for S3 and 14% for F3. The optimum multiplicity of infection (MOI) for S3 was 1:1 and 2:1 for F3. From the one-step growth curve, both the latent periods of S3 and F3 were estimated to be 30 and 20 min, and the burst sizes showed 5.8 and 4.6 (PFU)/infected cells, respectively. The D10 values of the most two antimicrobial-resistant strains (E. coli-2 and E. coli-10) were calculated, showing nearly identical values (0.37 and 0.38 kGy), respectively. Both coliphages were used, either alone or in combination with electron beam irradiation (EBI), to eradicate the most multidrug-resistant E. coli in domestic wastewater. EBI reduced the counts of E. coli-2 and -10 by 59% and 65%, respectively. While the combination of coliphages and EBI completely eradicated these microbes. Combination of each individual coliphage and EBI decreased the growth of E. coli in domestic wastewater to an undetectable level.