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