Molecular Identification, Phylogenetic Analysis, and Antibiotic Susceptibility Profiles of Bacteria Isolated from Borehole Water across Seasonal Variations

Abstract

Groundwater serves as a major source of potable water in many developing regions; however, its microbiological quality remains a public health concern. This study evaluated the bacterial diversity, seasonal variation, molecular identification, phylogenetic relationships, and antibiotic susceptibility profiles of bacteria isolated from borehole water sources. Total bacterial counts were determined for both rainy and dry seasons, revealing values ranging from 3.65–3.92 Log CFU/mL and 3.54–3.83 Log CFU/mL, respectively, with slightly higher counts observed during the rainy season. Bacterial isolates were identified using 16S rRNA gene sequencing and analyzed through BLASTn, which confirmed high similarity (97.88 – 99.86 %) with known species including Escherichia coli, Klebsiella aerogenes, Salmonella enterica, Proteus mirabilis, Pseudomonas aeruginosa, and Pseudomonas fluorescens. Phylogenetic analysis using the Neighbor-Joining method revealed clear clustering of isolates with reference strains, supported by high bootstrap values. Antibiotic susceptibility testing showed that most isolates were sensitive to fluoroquinolones, with ciprofloxacin demonstrating the highest efficacy. The findings highlight the presence of potentially pathogenic bacteria in borehole water and underscore the importance of continuous monitoring and appropriate water treatment strategies to safeguard public health.