Metal tolerance analysis of Gram negative bacteria from hospital effluents of Northern India

Effluents from different hospitals were analysed to Nickel, Chromium, Cobalt, Copper, Mercury, Cadmium and Zinc resistance among Gram negative bacteria. The resistance among the Gram negative bacterial population varied considerably in different metal and water sampling sites. Gram negative bacteria showed lower metal resistant viable count range 4.01 x104-1.3 x103 at 50-100 μg/ml in site-IV as compared to 11.03x105-1.03x104, 12.02x105-1.4x103 and 12.33x105-2.7x103 in site-I, II and III against all metal tested, respectively. Viable counts of Gram negative bacterial population were recorded higher against Nickel and Zinc from sampling site-III as compared to other sites tested. Lower viable counts of Gram negative bacteria were recorded against Mercury in all sites tested. All the isolates of Gram negative bacteria showed their tolerance level (Minimum inhibitory concentration) in the range of 50-1600μg/ml against all the metal tested. Of 88%, 76% and 86% isolates exhibited their MIC at 50-100 μg/ml against Mercury, Cadmium and Cobalt in all the sites tested, respectively. Maximum 60% and 32% of the isolates demonstrated their MIC at 1200-1600 μg/ml against Cr2+ and Cu2+ from the entire site tested, respectively. All Gram negative bacterial isolates also observed multiple resistance patterns (2-7 metal) in different combination of metals. The Multi metal resistance Index (MMR) index ranges were found (0.03-0.71) indicating the high risk of environmental contamination and emergence of metal resistance which may promote the development of resistance to antibiotics among the pathogens.