ABSTRACT

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.

Keywords: Antinbiotics, Toxicity, Assay, Synergistic, effluence