Cluster Analysis of Oxytetracycline and Chloramphenicol Susceptibility in Aeromonas spp. and Escherichia coli from an Aquaculture Environment

Abstract

Introduction: The worldwide growth of aquaculture has led to persistent infections and the emergence of antibiotic-resistant bacteria (ARB). The present study identified the similarity and correlativity of antibiotic susceptibility in the autochthonous bacterial flora of carps cultured in the East Kolkata Wetland and peri-urban Kolkata, India using clustering algorithms based on minimal inhibitory concentration (MIC) data. Materials and Methods: Motile Aeromonas spp. and Escherichia coli (50 each) isolated in selective media from carps and their environment were tested for susceptibility to oxytetracycline (OTC) and chloramphenicol (CH) using the agar-disc diffusion assay. The MICs of these two antibiotics were determined using the agar dilution method and clustered using the BioNumerics 7.6 software package. Results: The MICs of OTC and CH varied from 0.39 to 50 µg/ml and 1.56 to >100 µg/ml, respectively. Dendrogram-based cluster analysis of motile aeromonads showed relatively high internal homogeneity, as >5 subgroups were obtained under the main clusters. Escherichia coli also showed high internal homogeneity. Dendrogram-based advanced nodal cluster analysis of motile aeromonads as a group yielded a greater number of clusters. Conclusion: The varied susceptibility among motile aeromonads and E. coli isolated from an aquaculture environment with no history of antibiotic use implied the possible contamination of carps with ARB from domestic and hospital effluents. Nevertheless, E. coli strains isolated from this environment exhibited high heterogeneity in antibiotic susceptibility, which is a serious cause for concern.

Keywords

• motile aeromonads
• escherichia coli
• antibiotics
• minimal inhibitory concentration
• cluster analysis