Antimicrobial Susceptibility and Biofilm-Forming Ability of Airborne Bacteria Isolated from Selected Livestock Farms and Abattoirs in Port Harcourt, Nigeria

Abstract

Background: Airborne microbial contamination in livestock farms and abattoirs poses significant public health, animal welfare, and food safety risks because of high animal density, inadequate ventilation, and processing activities that generate bioaerosols. Materials and Methods: This study assessed the distribution, diversity, antibiotic susceptibility, and biofilm-forming potential of airborne microorganisms in six livestock-related environments in Port Harcourt, Nigeria: Piggery Farm, Goat Farm, Cattle Farm, Rumuokoro Abattoir, Eagle Island Abattoir, and Tech Farm Abattoir. Air samples were collected by passive sedimentation using exposed Nutrient Agar, MacConkey Agar, and Sabouraud Dextrose Agar plates placed in areas of high animal activity, waste disposal, and slaughter-processing operations for 10 minutes. The plates were incubated at 37°C for 24–72 hours. Bacterial isolates were identified using colonial morphology, Gram staining, and standard biochemical tests, while fungal isolates were identified based on their macroscopic and microscopic characteristics. Antibiotic susceptibility was determined using the Kirby–Bauer disc diffusion method, and microbial load was expressed as colony-forming units per minute per square metre (CFU/min·m²).   Results: Rumuokoro Abattoir recorded the highest microbial load, with total heterotrophic bacterial count, total coliform count, and total fungal count of 36.38 ± 15.91, 38.60 ± 18.24, and 5.10 ± 0.28 CFU/min·m², respectively. A total of 24 bacterial isolates belonging to nine genera were identified, comprising Staphylococcus spp., Bacillus spp., Lederbergia sp., Micrococcus sp., Serratia spp., Arsenophonus sp., Cronobacter sp., Klebsiella spp., and Citrobacter spp. Staphylococcus spp. showed the highest occurrence (29.2%), followed by Bacillus spp. (20.8%). Five fungal taxa were recovered: Penicillium sp., Mucor sp., Aspergillus niger, Trichophyton sp., and Fusarium sp. Antibiotic susceptibility testing showed that most Bacillus spp. and Staphylococcus spp. were resistant to rifampicin, ceftazidime, azithromycin, and cefuroxime, with only limited susceptibility to gentamicin and levofloxacin. Among the Gram-negative isolates, Serratia spp. and Citrobacter spp. were resistant to all antibiotics tested, whereas Klebsiella spp. and Cronobacter spp. exhibited susceptibility to selected antibiotics with some intermediate responses. Biofilm production was detected in Klebsiella spp., Citrobacter spp., and Bacillus spp. Conclusion: The livestock farms and abattoirs in the study areas harbours diverse airborne microorganisms, including antibiotic-resistant and biofilm-forming bacterial species, with abattoirs exhibiting the highest microbial contamination.