Antibacterial agents and heavy metal resistance in Gram-negative bacteria isolated from seawater, shrimp and sediment in Iskenderun Bay, Turkey

Abstract

The aim of the present study was to determine the level of antibiotic resistance patterns and distribution of heavy metal resistance of bacterial isolates from seawater, sediment and shrimps, and to determine if there is a relationship between antibiotic and heavy metal resistance. We undertook studies in 2007 in the industrially polluted Iskenderun Bay, on the south coast of Turkey. The resistance of 236 Gram-negative bacterial isolates (49 from seawater, 90 from sediment and 97 from shrimp) to 16 different antibiotics, and to 5 heavy metals, was investigated by agar diffusion and agar dilution methods, respectively. A total of 31 species of bacteria were isolated: the most common strains isolated from all samples were Escherichia coli (11.4%), Aeromonas hydrophila (9.7%) and Stenotrophomonas maltophilia (9.3%). There was a high incidence of resistance to ampicillin (93.2%), streptomycin (90.2%) and cefazolin (81.3%), and a low incidence of resistance to imipenem (16.5%), meropenem (13.9%) and cefepime (8.0%). Some 56.8% of all bacteria isolated from seawater, sediment and shrimp were resistant to 7 or more antibiotics. Most isolates showed tolerance to different concentrations of heavy metals, and minimal inhibition concentrations ranged from 12.5 μg/ml to > 3200 μg/ml. The bacteria from seawater, sediment and shrimp showed high resistance to cadmium of 69.4%, 88.9%, and 81.1% respectively, and low resistance to manganese of 2%, 6.7% and 11.3% respectively. The seawater and sediment isolates which were metal resistant also showed a high resistance to three antibiotics: streptomycin, ampicillin and trimethoprim-sulphamethoxazole. In contrast, the shrimp isolates which were metal resistant were resistant to four antibiotics: cefazolin, nitrofurantoin, cefuroxime and ampicillin. Our results show that Iskenderun Bay has a significant proportion of antibiotic and heavy metal resistant Gram-negative bacteria, and these bacteria constitute a potential risk for public health.