One hundred strains of Gram-negative bacteria were isolated from a brackish water Lagoon, Kucukcekmece in Istanbul-Turkey. Identification studies showed that 31% of the isolated bacteria were Escherichia colt, 28% were Citrobacter, and 12% were Enterobacter. Antibiotic and heavy metal resistances exhibited by these bacteria were evaluated. In antibiotic susceptibility tests, 68% of the isolates appeared to be resistant to vancomycin, while 38% was resistant to erythromycin, 23% to penicilin G, 19% to ampicillin, 13% to nalidixic acid and streptomycin, 7% to chloramphenicol, 5% to amikacin, 2% to gentamycin, and 1% to kanamycin. Most of the isolates tolerated various concentrations of heavy metals, and the minimum inhibitory concentrations (MIC) ranged from 20 mu g/ml to >5000 mu g/ml. In terms of heavy metal sensitivity, 98% of the isolates were resistant to Fe, 95% to Cd, 85% to Co, 83% to Cu and Zn, and 74% to Ni. When antibiotic-heavy metals multiresistance index was examined, it was determined that the multiple heavy metal resistance (MHMR) index was remarkably high for the bacteria, while the multiple antibiotic resistance (MAR) index was low according to heavy metal resistance
