JOURNAL OF BACTERIOLOGY AND VIROLOGY ISSN:1598-2467(Print) 2093-0429(Online)

Landfill ecosystems are increasingly recognized as environmental reservoirs of antimicrobial resistance (AMR), yet information from the Philippines remains limited. This study characterized the physicochemical properties of landfill sediments and examined their relationships with the cultivable bacterial community and antimicrobial resistance in the Calajunan Sanitary Landfill, Iloilo City, Philippines. Sediment samples were collected from five functional zones representing organic, medical, mixed-waste, and leachate-impacted areas. Significant spatial variation (p < 0.05) was observed in sediment pH, organic carbon, nutrient content, and moisture. Total heterotrophic plate counts ranged from 7.05 to 7.89 log₁₀ CFU/g, with the highest counts recorded in the organic-rich station. A total of 489 bacterial isolates were recovered and identified by biochemical characterization and 16S rRNA gene sequencing (99.63–100% sequence similarity). The cultivable bacterial community was dominated by Bacillus spp., together with opportunistic Gram-negative genera including Aeromonas, Citrobacter, Enterobacter, Klebsiella, Morganella, Proteus, Providencia, and Pseudomonas. Spearman's correlation analysis identified organic carbon, total nitrogen, pH, and calcium as the sediment properties most closely associated with bacterial distribution. Following exclusion of intrinsic resistance according to current EUCAST recommendations, acquired resistance was most frequent against β-lactams, macrolides, aminoglycosides, nitrofurans, and tetracyclines. MAR indices ranged from 0.1 to 0.8, with most bacterial taxa exhibiting values ≥0.2 and several species exhibiting values ≥0.4. This study provides the first baseline characterization of cultivable landfill bacterial communities in Western Visayas and demonstrates that landfill sediments are important environmental reservoirs of antimicrobial-resistant bacteria, supporting their inclusion in One Health-based AMR surveillance.