Phenotypic Profiling of Multi-antibiotic Resistant Bacteria from Abattoir Effluent-impacted Soil: Implications for Environmental Health and Food Safety

Abstract

Antimicrobial resistance (AMR) is an emerging public health challenge, with abattoir effluent-contaminated soils serving as potential reservoirs of resistant bacteria. This study evaluated the antibiotic resistance profile of bacteria isolated from abattoir effluent-impacted soil (AEIS) obtained from an abattoir at Yenagoa, Bayelsa State. The soil sample was analysed for physico-chemical properties using standard analytical techniques. Isolation, enumeration, and identification of bacterial species were performed using standard microbiological and molecular methods. Antibiotic resistance profiling of the isolates was done using the Kirby–Bauer disc diffusion method. The AEIS pH (7.73) was above the standard permissible range (6.5-7.5), electrical conductivity (1,336 µS/cm), organic carbon (2.99%) and organic matter (5.14%) were within standard permissible limits; however, nitrate (3.82 mg/kg) and phosphate (1.40 mg/kg) were below standard permissible limits of 10-50 mg/kg and 5-30 mg/kg, respectively. Bacterial counts were 5.0 × 106±1.0 CFU/g on Blood agar, 5.4 × 105±4.0 CFU/g on Salmonella–Shigella agar, and too numerous to count (> 300 colonies) on Mannitol Salt agar. Biochemical tests identified two of the isolates as Salmonella sp. and Staphylococcus sp., while the others were identified via 16S rRNA gene sequencing as Proteus mirabilis and Kluyvera cryocrescens. Antibiotic resistance testing revealed multi-antibiotic resistance among Gram-negative isolates, with Salmonella sp., P. mirabilis and K. cryocrescens exhibiting resistance to cephems/cephalosporins, penicillins, β-lactam combination agents, and carbapenems, whereas Staphylococcus sp. was susceptible to all tested antibiotics. Multi-antibiotic resistance indices ranged from 0.33 to 0.58, exceeding the 0.2 threshold and indicating exposure to high-risk contamination sources. These findings demonstrate that the studied abattoir effluent-impacted soil serves as a reservoir for multi-antibiotic-resistant bacteria with potential environmental and food safety implications. Effective abattoir waste management, environmental monitoring, and antimicrobial stewardship are therefore recommended to reduce the spread of antibiotic-resistant bacteria.