Waste Water Bacterial Isolates Resistant to Heavy Metals and Antibiotics

Sewage water of Casablanca, an industrial city in Morocco, was studied for microorganisms resistant to heavy metals. Isolates were purified and collected on agar slants to be screened for resistance to heavy metals, including mercury in vitro. The strains that showed high resistance to heavy metals were also studied for their resistance to antibiotics and aromatic hydrocarbons. Results indicated that the strains most resistant to all tested products belonged to Ps. fluorescens, Ps. aeruginosa, Klebsiella pneumoniae, Proteus mirabilis, and Staphylococcus sp. These strains exhibit high minimal inhibitory concentrations for heavy metals such as cadmium (2 mm) or mercury (1.2 mm). Growth of Ps. fluorescens and Klebsiella pneumoniae in the presence of heavy metals was also determined, and the growth curves indicated that mercury, copper, and zinc present a slight inhibitory action, while cadmium and silver could have a potent inhibitory action on growth compared with the controls. These studies also investigated growth in media containing aromatic compounds as the sole source of carbon. The results demonstrate that these strains could be good candidates for remediation of some heavy metals and aromatic compounds in heavily polluted sites. Received: 23 December 1999 / Accepted: 6 April 2000