TOXICITY OF SINGLE AND QUATENARY MIXTURE OF ANTIBIOTICS TO NATURAL MICROBIAL COMMUNITY

The toxicities of single antibiotics: ciprofloxacin, azithromycin, sulfathiazole and amoxicillin and their quaternary mixtures in different ratios were examined on three organisms Staphylococcus aureus, Bacillus cereus and Micrococcus luteus all isolated from Nworie River from three different points including the point of effluent discharge of a hospital. Toxicity of antibiotics and mixtures was assessed using inhibition of total dehydrogenase assay method. Result obtained from the study showed that Bacillus cereus isolated from the effluent point of discharge was more resistant to the drug mixtures. The trend of toxicity of the four antibiotics can be ranked as azithromycin > ciprofloxacin > sulphathiazole > amoxicillin. The toxicological unit of the quaternary mixture of ciprofloxacin, azithromycin, sulfathiazole and amoxicillin in the ratio 30:30:20:20 proved to be very toxic and had synergistic effect against all three isolates, while the equal mixtures of the four antibiotics proved to be strongly antagonistic and had very low effect against the three organisms. The risk quotient assessment of the antibiotics and their mixtures showed values higher than 1 for the drug mixture 30:30:20:20, while amoxicillin and sulfathiazole posed no ecological risk. Bacillus cereus which was the organism isolated from the point of effluent discharge was more resistant to the effect of the antibiotics mixture than Micrococcus luteus and Staphylococcus aureus. Antibiotics released into the environment deserve attention as some of their mixtures are harmful to the aquatic ecosystem and hence the need for control of the use and effluence especially from hospitals.