HIGH-LEVELS OF MULTIPLE METAL RESISTANCE AND ITS CORRELATION TO ANTIBIOTIC-RESISTANCE IN ENVIRONMENTAL ISOLATES OF ACINETOBACTER

Forty strains of Acinetobacter were isolated from different environmen tal sources. All the strains were classified into four genospecies, i. e. A. baumannii (33 isolates), A. calcoaceticus (three isolates), A. j unii (three isolates) and A. genospecies3 (one isolate). Susceptibilit y of these 40 strains to salts of 20 heavy metals and 18 antibiotics w as tested by the agar dilution method. All environmental isolates of A cinetobacter were resistant to multiple metal ions (minimum 13 metal i ons) while all but one of the strains were resistant to multiple antib iotics (minimum four antibiotics). The maximum number of strains were found to be sensitive to mercury (60% strains) while all strains were resistant to copper, lead, boron and tungsten even at 10 mm concentrat ion. Salts of these four metal ions may be added to the growth medium to facilitate selective isolation of Acinetobacter. Rifampicin and nal idixic acid were the most toxic antibiotics, inhibiting 94.5 and 89.5% of the acinetobacters, respectively. A. genospecies3 was found to be the most resistant species, tolerating high concentrations of all the 20 metal ions and also to a greater number of antibiotics than any oth er species of Acinetobacter tested. An inhibitory concentration (10 mm ) of Ni2+ and Zn2+ was observed to inhibit the growth of all of the cl inical isolates but allowed the growth of the environmental isolates, facilitating the differentiation between pathogenic and non-pathogenic acinetobacters.