Bacterial density and antibiotic resistance of Aeromonas sp. in organs of metal-stressed freshwater fish Channa punctatus

Abstract

Bacterial density was observed in liver, spleen, kidneys, muscles, and gills of freshwater fish Channa punctatus under stress from heavy metals including cadmium (Cd), chromium (Cr) (hexavalent) and lead (Pb) individually. Maximum density of aerobic heterotrophic bacteria was observed as colony forming units per gram (cfu gm⁻¹) of gills (TNTC), kidneys (2.8 × 10⁴ cfu gm⁻¹) and liver (1 × 10⁴ c.f.u. gm⁻¹) after Cd exposure followed by muscles (9.5 × 10³ cfu gm⁻¹) and spleen (8 × 10³ cfu gm⁻¹) after exposure to Pb and Cr, respectively. Random isolates, identified as Aeromonas sp., were examined for their antibiotic susceptibility and hemolytic activity. Multiple antibiotic resistance (MAR) to amoxycillin, chloramphenicol, nalidixic acid, and trimethoprim was exhibited by 50–90% of test aeromonads. Production of α-hemolysin was shown by 3% of isolates with β-hemolysin by 5% of isolates of Aeromonas sp. These data indicate that pollution due to toxic metals in aquatic ecosystem enhances density and pathogenic characteristics of bacteria in fish organs, which may pose a risk to fish fauna and public health.

Keywords:

• water
• metal
• bacteria
• antibiotic resistance

Acknowledgements

Authors are thankful to the Director, Indian Institute of Toxicology Research, Lucknow for his guidance and Council of Scientific and Industrial Research (CSIR), India, for financial support to complete this study. Thanks also to Mr Pyare Lal for his technical assistance during the study.