The global increase in resistance to critically important antibiotics poses a serious public health threat, particularly due to mobile antibiotic resistance genes (ARGs) that facilitate rapid spread among bacteria through horizontal gene transfer. This study was conducted to assess antibiotic resistance genes and antibiotic resistance patterns in bacterial isolates from selected borehole water around open dump sites in the Onitsha South metropolis. Ten (10) borehole water samples were aseptically collected from ten (10) different boreholes 50 to 100m distance from the open dump sites and transported to Nnamdi Azikiwe University microbiology laboratory for microbial analysis. The membrane filtration method was used for the enumeration of total coliforms and fecal coliforms in the water samples, while serial dilution and pour plate methods were used for total heterotrophic bacterial counts. Bacterial isolates were identified based on cultural, morphological, and biochemical characteristics. Antibiotic susceptibility testing was carried out on the bacterial isolates using the Kirby-Bauer method, and results were interpreted in accordance with standard guidelines. The multiple antibiotic resistance (MAR) index was calculated for each isolate to assess antibiotic exposure levels. Antibiotic-resistant genes present in the MAR isolates were assessed by polymerase chain reaction (PCR) amplification of resistance genes (blaNDM, blaCTX-M, aac(6’)-Ib-cr ) followed by visualization by agarose gel electrophoresis. The isolates suspected in the water samples include Staphylococcus aureus (37.5%), Bacillus specie (25.0%), Vibrio specie, Staphylococcus specie,  and Escherichia coli are 8.3% respectively,  while Shigella specie, Klebsiella specie,  and Salmonella specie are 4.3% respectively. The results showed widespread bacterial contamination, with a high prevalence of multidrug resistance among isolates. Ceftazidime and Cefuroxime were resistant to 100% of the Gram-positive isolates while Levofloxacin was resistant to 63.2% of the Gram-positive isolates. All the antibiotics were resistant to 100% of the Gram-negative isolates except streptomycin which was resistant to 60% of the Gram-negative isolates. MAR index values ranged from 0.5 to 1.0, with 100% of the isolates showing values > 0.2, an indication of exposure to high-risk sources of contamination. PCR showed 100% detection of blaNDM in all the selected isolates, blaCTX-M was detected in 33.3% of the isolates selected, while aac(6')-Ib-cr was not detected in any of the isolate. This study calls attention to routine water quality monitoring, improved sanitation practices, and strict regulation of antibiotic use in Nigeria.