Stress of Five Heavy Metals on the Resistance of Isolates from Swine Wastewater to Four Antibiotics

Abstract

Co-existence of heavy metals and antibiotics becomes increasingly common in environmental pollution. To investigate the stress of heavy metals on microbial resistance to antibiotics, fifty-six strains of bacteria were initially isolated from some swine water in Guangzhou city, based on their resistance to four antibiotics (cefradine, norfloxacin, amoxicillin, tetracycline) and five heavy metals (Pb2+, Cr(VI), Hg2+, Cu2+, Zn2+), a gram-negative isolate, Pseudomonas putida XX6, was selected to study the detail stress rules of heavy metals on its resistance to antibiotics. The antibiotics incidences of these isolates were in the order of norfloxacin>amoxicillin>cefradine>tetracycline, and that of P. putida XX6 was  cefradine>amoxicillin≈tetracycline>norfloxacin. The addition of heavy metals made all isolates’  resistance to antibiotics decrease, and Cr(VI) impacted their resistance to norfloxacin most obviously. If the concentration of heavy metals was the most important factor affecting the resistance of P. putida XX6 to the antibiotics? There was a positive correlation between the bacterial resistances to antibiotics and heavy metals of low concentrations, and the correlation turned to negative with the concentrations of heavy metals increasing. But the bacterial resistance to amoxicillin or cefradine remained irrelevant to the concentrations of Cr (VI) or Pb2+. Results showed that the combined effect of antibiotics and heavy metals could alter their individual effect on bio-toxicity as well as on the biological removal capability of pollutants.