In the process of determining the bacteriological quality of water from the Opa River, samples were taken from the river at five different points on five separate occasions. These samples were analysed by the most probable number method and by filtration, and the bacterial isolates obtained were identified by standard methods. The isolates obtained were tested for their resistance to thirteen antibiotics using the disc agar diffusion method, and four of the isolates were further tested for their ability to transfer their antibiotic resistances by conjugation. The microbial load at the different sampling points ranged between 0.01 × 102 and more than 300 × 102 while the most probable number of coliforms in 100 ml of samples were in excess of 1,800 cfu. The organisms most frequently isolated from the samples included those of the Genera Enterobacter, Enterococcus, Klebsiella, Flavobacteria, Proteus and Streptobacillus. The Opa River was found to be contaminated along its length by multiply antibiotic resistant organisms, some of which had the ability to transfer their resistance to another organism. Antibiotics to which the isolates were resistant included tetracycline (100%), ampicillin (98.9%), cephalothin (95.5%), doxycycline (92.4%), chloramphenicol (25.8%), tobromycin (24.2%) and spectionomycin (21.1%). Approximately, 30% of the isolates were resistant to norfloxacin while 6.1% were resistant to ciprofloxacin. The transferable resistances included those to tetracycline, cephalothin, trimethoprim and erythromycin. The Opa River is a source of antibiotic resistant organisms, and the presence of such organisms in this body of water which is used for many purposes within the area suggests a means whereby these organisms and the antibiotic resistances which they carry can spread through the populations that come in contact with the river.
Key words: Antibiotic resistance, contamination, Opa River, South-Western Nigeria.
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