Molecular characterization and human health risk assessment of multi-drug and heavy metals tolerant bacteria from urban river water

Abstract

The present study characterized the multi-drug and heavy metal-resistant bacteria and their human health risks in the six major urban rivers. The bacterial strains were identified by molecular techniques based on 16 s rDNA gene sequence analysis, where most of the isolates belong to Bacillus spp. and Staphylococcus spp. The minimum inhibitory concentration (MIC) of the bacterial strains to different heavy metals like chromium, lead, cadmium, cobalt, mercury, and nickel ranged up to 3000 mg/L. The antibiotic susceptibility tests revealed that 69.23% of the strains resistant to ceftriaxone, while 61.54% were resilient to cefotaxime, 53.85% to ampicillin, 46.15% to amoxicillin, 30.77% to streptomycin, 15.38% to azithromycin, 15.38% to chloramphenicol, 7.69% to tetracycline, 7.69% to gentamycin, 7.69% to vancomycin. Interestingly, ciprofloxacin was found highly sensitive to all the bacterial strains in the present study. The multiple heavy metals resistance (MHMR) index of all the bacterial strains in the present study was very high compared to the standard value of 0.50. The multiple antibiotics resistance (MAR) index was highest for Bacillus cereus MKSMPbT1 (0.45), while it was lowest in B. xiamenesis MKSMCrB1 and B. pumilus MKSMNiT1 (0.09). The results of the hemolytic assay revealed that almost all the bacterial strains identified in the present study are highly pathogenic in nature. In essence, the bacterial strains identified in the present study could pose significant environmental and public health concerns that draw strict government attention.