ESCHERICHIA COLI AN INDICATOR OF ENVIRONMENTAL POLLUTION: INFECTIOUS RESISTANCE AGAINST HEAVY METALS/METALLOID IN E. COLI AND FREQUENCY OF THEIR CO-TKANSFER

摘要

Two hundred and eighty four strains of Escleriehia coli belonging to various pathological conditions of man and animals (103 from UTI and 49 from GTI of human beings : 77 from borine, 7 from ovine GTI and 48 from urinogenital tract infections of equines) were screened for the prevalence of metil resistance against cadmium, cobalt, nickel, mercury, silver, copper and a metalloid of arsenic (sodium arsenite). A new system of" evaluating the resistance was prooosed . All MIC values of different E. colistrains were compared with MIC values oi standard strain E. celi and were expressed as EGB-units. Four or more of ECB units were taken as the level of resistance. Nearly, 154 (54.23%) strains could be distinguished as 'resistant' strains which were resistant to either single or in combination with other metals. The highest resistance was recorded againstCo (40.14%) followed by Hg (19.17%), Ag (6.33%) As (2.11%) and least to Cd and Ni (1.05% each). The strains showed every high resistance towards mercuric chloride (toierat-inp even upto 32 ECU units). Resistance to single metal was observed among 73.88% of the strains, while resistance to double and triple metals was exhibited by 24 03%) and 2.59% of strains respectively. Strains of human origin were found more resistant (to metals as compared to animal strains (43.18%). Metal resistance was prevalent more (74.76%) among strains from UTI as compared to GTI (40.82%) in human origins. Nearly HO E. coli strains harbouring several metal resistance determinants simultaneously were exposed for conjugal transfer of metal-resistance plasmids. About 41.82% of the strains could transfer their resistance against 4 meUls (Hg, Co, Ni and As) in various pattern. Single resi>tmce transfer being highest '91.3%) followed by double (6.25%) and triple (2.17%) metal resistance. Transfer of resistance to Cd, Ag and Cu could not be recorded. Mercury resistance was transferred most frequently (50%) followed by nickel (23.28%) cobalt and sodium aisenite (6.25% each). The effect of acridine orange, a DNA inhibitor, was examined on 35 selccted E. coli strains having multiple resistance markers. The plasmids responcible for resistance to Hg, Co. Ni and As could be partially or completely cured by acridine orange. Its effect was limited on elimination of resistance markers to Cd, Ag and Cu. Elimination frequencies ot resistance factors differed greatly with different metals, indicating thereby a heferogenicity of DNA strtnds (plasmids) coding tor resistance to various metallic ions. The plasmids envolved in coding resistance for Hg, Co, Ni, and As are clinically important, thus their infectious spread among enterobacteriaceae group of organisms is hazardirms to human and animal health. The presence of metal resistance in E.ctli strains is an direct indication of environmental pollution by such metals. Therefore E. coli mains can be used as an indicator of environmental pollution.