Assessment of thermotolerant coliforms, Escherichia coli, and Pseudomonas aeruginosa throughout a drinking water treatment plant and supply system in Culiacan, Mexico

Beyond conventional fecal indicators, opportunistic pathogens like Pseudomonas aeruginosa warrant closer examination. This study quantified thermotolerant coliforms, Escherichia coli, and P. aeruginosa in potable water in Culiacán, Sinaloa, México. Monthly stratified sampling (January–August 2024) was conducted at two treatment plants. In the same period, tap water, 20-L bottled water, and dispenser water were randomly sampled at 30 households from Northern and Southern city sections. Microorganisms were enumerated by membrane filtration using CHROMagar ECC and Cetrimide agar. In treatment plant samples, 81% showed no microbial contamination; household contamination was higher in the Southern (64%) than Northern area (41%), suggesting local factors require further investigation. Thermotolerant coliforms (29%), E. coli (3%), and P. aeruginosa (20%) were detected in household samples, indicating potential distribution or handling deficiencies. Higher bacterial mean concentrations were observed in bottled water (thermotolerant coliforms: 1.98 ± 1.49 Log CFU 100mL−1; P. aeruginosa: 3.19 ± 3.07 Log CFU·100mL−1) and dispenser water (thermotolerant coliforms: 2.23 ± 1.79 Log CFU·100mL−1; P. aeruginosa: 3.13 ± 3.02 Log CFU·100mL−1), with 34% of bottled samples exceeding national limits. These findings underscore the need for expanded microbial surveillance, including opportunistic pathogens, and strategies to ensure microbiological safety throughout the distribution network and commercial presentations.