Abundance, Diversity, and Antibiotic Resistance of Aeromonas spp. in Well Water from Selected Barangays in Iloilo City, Philippines

Abstract

This study investigated the abundance, diversity, and antibiotic resistance patterns of Aeromonas spp. in well water from five selected barangays (villages) in Iloilo City, alongside heterotrophic bacterial counts and physicochemical parameters during the dry (March to May) and wet (June to August) seasons. Presumptive Aeromonas counts reached 10³ CFU/mL during the dry season and 10² CFU/mL during the wet season, while heterotrophic plate counts peaked at 10⁴ CFU/mL and 10³ CFU/mL, respectively. Seasonal variations significantly influenced water quality, with higher temperatures, biochemical oxygen demand, and total dissolved solids recorded during the dry season, while dissolved oxygen levels were elevated during the wet season (p < 0.05). Aeromonas hydrophila was the most prevalent (59%), followed by A. veronii (21%). Other predominant bacterial species included Escherichia coli (12%), Enterococcus faecium (5%), and Staphylococcus aureus (7%), the latter found only in the wet season. Antimicrobial susceptibility testing of 10 antibiotics commonly used in human-veterinary medicine, and aquaculture, revealed high resistance to amoxicillin (A. hydrophila: 98.6%; A. veronii: 96%; E. faecium: 100%; E. coli: 100%; S. aureus: 100%), erythromycin (100%; 60%; 100%; 100%; 100%), and neomycin (97.1%; 92%; 50%; 57.1%; 100%). Multidrug resistance was widespread, with MAR indices exceeding 0.2, indicating substantial antibiotic exposure and contamination from high-risk sources. This is the first report on the load, composition, and antibiotic resistance of Aeromonas spp. in well water in the Philippines, underscoring the need for continuous microbial monitoring, improved well-water disinfection, and strengthened antibiotic stewardship to mitigate public health risks associated with contaminated groundwater sources.