Abstract

The pollution of marine environment with heavy metals, antibiotics, dyes and surfactants may possess a serious threat to human life and the other organisms because of their toxicity and ability to persist for long time. The metals and antibiotics resistance of 48 heterotrophic bacterial isolates from hospital waste water and polluted sea water were studied. The minimum inhibitory concentrations (MICs) of heavy metals were different for each isolate. All isolates showed high resistance to nickel, chromium, barium and copper. On the other hand, mercury was the highest toxic metal against all the isolates. The frequencies of resistance for all isolates to each metal ion tested were as follows: Ni, 88%; Ba, 88%; Cr, 75%; Cu, 38% and Hg, 13% for hospital waste water isolates, and Ni, 88%; Ba, 75%; Cr, 50%; Cu, 50%  and Hg, 0% for seawater bacteria. The response of the isolates to five antibiotics was tested; it ranged from complete resistance to total sensitivity. The hospital waste water isolates showed resistance for 4 of 5 antibiotics with percentages that ranged from 13 to 100%. On the other hand, 88% of seawater isolates resisted only one antibiotic. Multiple-metal resistance was exhibited by 100% of heterotrophic bacteria, while penta-metal-resistant bacteria was observed only in hospital waste water isolates. Multiple-antibiotic resistance was exhibited by 63% of the hospital waste water bacteria. The highest incidence of metal-antibiotic double resistance was observed in hospital waste water isolates compared with sea water isolates. Moreover, all isolates exhibited multiple resistances for different dyes as crystal violet, iodine and sufranine and other chemicals such as sodium lurayl sulfate. The bacterial isolates from hospital waste water showed higher resistance to dyes and surfactant than those isolated from polluted seawater. The composition of bacterial communities which were resistant to different chemicals ranged from 0.02 to 0.33% for the bacterial pathogens and from 1.95 to 15.0% for the fecal bacteria in the hospital waste water whereas, in seawater samples, the percentages of bacterial pathogens ranged from 0.04 to 0.12% and the percentages fecal bacteria ranged from 0.95 to 29.10%. This finding suggests that the discharge of hospital waste water without preliminary treatment is an important source for the spread of new phenotype bacteria with multiple-resistance in natural habitats which can pose a public health risk.

Key words: Metal resistance, antibiotic resistance, heterotrophic bacteria, hospital waste water, polluted sea water.