Microbiological Risk Assessment of Drinking Water Using Integrated Phenotypic and Molecular Approaches in Guaranda

This study evaluates the microbiological quality of drinking water in the urban area of Guaranda through an integrated approach combining culture-based methods, biochemical characterization, and polymerase chain reaction (PCR) analysis. A total of 50 drinking water samples were collected from strategically selected points within the urban distribution system following Ecuadorian technical standards. Microbiological analyses included the detection of total and fecal coliforms, as well as the isolation and identification of Escherichia coli O157:H7, Salmonella spp., and Listeria monocytogenes. Culture-based analyses revealed that 22% of samples were positive for total coliforms and 4% for fecal coliforms. In selective culture media, contamination rates reached 18% for E. coli O157:H7, 8% for Salmonella spp., and 46% for Listeria monocytogenes. However, biochemical profiling showed substantial inconsistencies with the expected phenotypic characteristics of these pathogens, particularly in oxidase and citrate tests, suggesting possible false-positive identifications in complex environmental matrices. PCR assays confirmed lower detection frequencies, identifying E. coli O157:H7 and Salmonella spp. in 2% of samples each, and Listeria monocytogenes in 10% of samples. Agarose gel electrophoresis validated the amplification of specific DNA fragments of 212 bp, 244 bp, and 388 bp, respectively. The findings demonstrate significant discrepancies between conventional phenotypic methods and molecular techniques, highlighting the limitations of culture-based identification when used alone. This study emphasizes the importance of integrating molecular diagnostics into routine water quality monitoring programs to improve the reliability of pathogen detection and support more effective public health risk management in urban drinking water systems.