Microbiological Quality of Purified Water from Vending Machines: Occurrence, Antimicrobial Resistance, and Biofilm Formation of Pseudomonas aeruginosa

Purified water from vending machines offers consumers an alternative source of clean, safe water. However, data regarding its microbiological quality are limited, particularly concerning the prevalence of Pseudomonas aeruginosa harboring virulence traits. This study aimed to evaluate the microbiological quality of 125 purified water samples collected from vending machines across six cities of Michoacan, Mexico. Additionally, it sought to assess the occurrence of Pseudomonas aeruginosa and characterize its antimicrobial resistance profiles and biofilm-forming capacity. Aerobic mesophilic bacteria (AMB) were detected in all analyzed samples. A total of 71 (56.8%), 40 (32.0%), and 31 (24.8%) samples were positive for total coliforms (TC), fecal coliforms (FC), and Escherichia coli, respectively. Among the samples, 43 (34.4%) were positive for P. aeruginosa. There were significant correlations between the presence of P. aeruginosa and AMB (rho = 0.4445; p < 0.0001), TC (rho = 0.4094; p < 0.0001), FC (rho = 0.3389; p = 0.0001), and E. coli (rho = 0.3242; p = 0.0002). Moreover, the presence of TC in purified water samples increased the risk of P. aeruginosa nearly seven-fold (odds ratio = 6.91; p < 0.001). The resistance rate among P. aeruginosa strains to the most tested antibiotics ranged from 2.3 to 16.3%, and two (4.6%) of the isolates were multidrug-resistant. All P. aeruginosa strains were strong biofilm producers. Consequently, we recommend periodic maintenance of vending machines, the establishment of P. aeruginosa control protocols, and enhanced regulatory monitoring of the water vending industry.