Antimicrobial susceptibility profile of gram-negative bacteria isolated from selected hot springs in Laguna, Philippines

Geothermally heated hot springs often serve as reservoirs for diverse microorganisms, including pathogenic Gram-negative bacteria and potential carriers of antimicrobial resistance (AR). Thus, this study determined the microbial concentration and AR profiles of Gram-negative bacteria isolated from selected recreational hot springs in Calamba, Laguna, Philippines. The physicochemical parameters of the water were also analyzed to determine their correlations with the bacterial AR profiles. From 80 water samples collected over two months (March and April) in 2025 from four hot springs, the estimated average concentrations of Escherichia coli, total coliforms, and non-coliforms (in CFU/100 mL) were 93, 246, and 1,490, respectively. Two sampling sites failed to meet the Class B standards for primary contact recreation, as specified in the 2015 Guidelines for Recreational Waters Monitoring Program of the Philippine Department of Environment and Natural Resources. Moreover, antimicrobial susceptibility testing of 80 isolates against 21 antibiotics revealed low resistance rates, with key correlations identified between AR and environmental variables such as water temperature, pH, dissolved oxygen (DO), and conductivity. These findings suggest potential environmental influences on AR dynamics. However, the study's limited geographic scope and temporal coverage highlights the need for future longitudinal and broader geographic investigations. Nevertheless, the study provided baseline data for monitoring AR in recreational hot springs. It contributed to the understanding of AR ecology, offering insights for policymakers and researchers to design evidence-based strategies that mitigate the potential risk of contamination from runoff, maintain water quality standards, and safeguard public health.