Abstract
Aeromonas hydrophila strains isolated from different naturally polluted environments (ten from wastewater, six from bay used for aquaculture, eight from sea coast water and six from fish) were subjected to 13 antibiotics, and to four heavy metals (Copper, Cobalt, Zinc and Mercury) by using agar diffusion and agar dilution methods, respectively. In addition, effect of heavy metals on slime production was also investigated. Results of the antibiotic resistance agreed with those of heavy metals resistance, however, treated wastewater and bay strains were much tolerant than seawater and fish bacteria. The range of metal concentrations that was tolerated in the liquid media yielded information on the tolerance levels of A. hydrophila to different tested concentrations of metals. Copper and zinc were the best tolerated metals. Mercury was the most toxic component for all bacteria. Almost all A. hydrophila produced slime and a small number of strains have changed their morphotype under the heavy metals concentration. Our results have shown that Tunisian aquatic biotopes have a significant proportion of antibiotic and heavy metal resistant to A. hydrophila. Key words: Antibiotic resistance, Aeromonas hydrophila, heavy metals and slime producing.
Highlights
The anthropogenic contamination of the environment with heavy metals is a serious problem
In this work, we focus on the current body of knowledge regar-ding (i) to characterize the A. hydrophila strains recovered from Tunisian aquatic biotopes; (ii) to determine the level of antibiotic resistance rates against widely used antibiotics in Tunisia; (iii) to determine the heavy metals resistance of the bacteria; (iv) to investigate the relationship between the antibiotics and heavy metals resistance and (v) to determine the heavy metals effect on A. hydrophila slime producing
The results showed that bay, treated waste water A. hydrophila isolates were more resistant to almost tested antibiotics than sea water and fish A. hydrophila (nalidixic acid (70 and 60%), ticarcyline (60 and 50%), cefoxitine and cefalotine (100 and 90%)), respectively
Summary
The anthropogenic contamination of the environment with heavy metals is a serious problem. Fish farmers frequently use pharmaceuticals (such as antibiotics) and metal containing products to prevent fouling, to feed and to treat fish in order to limit the spread of infections (Burridge et al, 2010). Bacterial communities of aquacultures are strongly exposed to the combination of heavy metals and antibiotics. The exposure to both antimicrobial substances may increase the likelihood of selection and co-selection of antibiotic resistance. The high nutritional value and the relatively low cost of wastewater, excreta, and sewage sludge convert such heavy metal containing waste to valuable fish feed, especially in developing countries (WHO, 2006)
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