Antibiotic resistance profile of <i>Escherichia coli</i> from Marikina River in the Philippines: Environmental and public health implications

The Marikina River in the Philippines is faced with problems caused by urbanization through the indiscriminate discharge of agricultural and municipal effluents, thus making the river potentially take part in the transmission of antimicrobial resistance (AR). This study, therefore, focused on determining the concentration and AR profile of Escherichia coli isolated from surface waters across various river sites. The results showed that the concentration of E. coli from all six sampling sites, including one within a Philippine-protected landscape, has far exceeded the upper microbial limit for all water body classifications designated for beneficial use, including Class D water (400 CFU/100 mL). The estimated average E. coli and coliform concentrations from all sampling sites were 1.9 x 105 CFU/100 mL and 12.0 x 105 CFU/100 mL. Even in a protected area, average concentrations of E. coli (1.5 x 103 CFU/100 mL) and coliforms (5.6 x 103 CFU/100 mL) were far above the Class A water limit of 100 CFU/100 mL. Moreover, 18.8% and 22.9% of the isolates were classified as multidrug-resistant (MDR) and extended-spectrum beta-lactamase (ESBL) producers. Some isolates from the most upstream sites exhibited resistance to third-generation cephalosporins. These findings underscore the need for further surveillance, particularly in upstream areas, to better understand how human activities are contributing to the progression of AR in the river. Such studies are essential to keep authorities and policymakers informed and to guide more effective management and remediation efforts.