Fifty seven isolates of thermotolerant E. coli were recovered from 188 drinking water sources, 45 (78.9%) were typable of which 15 (26.3%) were pathogenic serotypes. Pathogenic serogroup obtained were 04 (Uropathogenic E. coli, UPEC), 025 (Enterotoxigenic E. coli, ETEC), 086 (Enteropathogenic E. coli, EPEC), 0103 (Shiga-toxin producing E. coli, STEC), 0157 (Shiga-toxin producing E. coli, STEC), 08 (Enterotoxigenic E. coli, ETEC) and 0113 (Shiga-toxin producing E. coli, STEC). All the pathogenic serotypes showed resistance to bacitracin and multiple heavy metal ions. Resistance to streptomycin and cotrimazole was detected in two strains whereas resistance to cephaloridine, polymixin-B and ampicillin was detected in one strain each. Transfer of resistances to drugs and metallic ions was observed in 9 out of 12 strains studied. Resistances to bacitracin were transferred in all nine strains. Among heavy metals resistance to As(3+) followed by Cr(6+) were transferred more frequently.
The antibiotic resistance and heavy metal tolerance pattern of 201 water borne thermotolerant coliforms isolated from rural areas were studied. Most of the isolates exhibited resistance to one or more antibiotics under study, and expressed tolerance to multiple metals. Twenty four strains representing different resistance combinations were tested for plasmid transfer to Escherichia coli K-12 recipient strain. Plasmid transfer was detected in all 24 strains studied for conjugation. Among antimicrobials bacitracin, ampicillin, and among metals nickel, copper, cadmium, cobalt, chromium and arsenic resistances were transferred most frequently. Linked transfer of antibiotics and metals was demonstrated in 12 strains. Thirty two cultures of thermotolerant coliforms were studied for R-plasmid curing using acridine orange. Among antibiotics, curing of resistance was observed for streptomycin, cephaloridine and kanamycin. Curing of resistance to nickel, copper, mercury, chromium, copper and arsenic were also observed. The potential health risk of plasmid mediated resistances to antibiotics and metal ions in coliforms isolated from rural drinking water sources is discussed.
Simple microbial test comprising H2S paper strip test, presence-absence (PA) test, and fluorogenic brila broth (BB) test performed directly at 44.5 degrees C were evaluated and compared with the standard most probable number (MPN) method for detection of fecal coliforms in 173 drinking water sources. BB and PA test were comparable with standard MPN method, whereas, poor compliance was noted for H2S test. PA test when compared with standard MPN test only 15% disagreement was detected, whereas, highest disagreement of 40% was observed in case of H2S test. BB test was found to be highly sensitive as only 7.8% disagreement with that of standard MPN test was found. Three hundred cultures obtained from positive tests were identified in order to evaluate the specificities of test used in detection of fecal indicator Escherichia coli. BB test was also found highly specific in detection of indicator organism as compared to PA and H2S test. Among the organisms isolated from BB test 84.4% of them were identified as E. coli as compared to 43.4 and 33.3 in PA and H2S test, respectively. The low incidence of recovery of E. coli (18.1%) for the standard MPN method places doubt on the validity of its application in tropical areas. The result of this investigation suggest that BB performed directly at 44.5 degrees C could be suitable cost effective test to assess the microbiological quality of drinking water in India and other tropical countries.
In a field study 78 water samples were analysed employing Fluorocult Brilla Broth (BB) and its performance was compared with standard MPN procedure. Out of 78 water samples analysed 56 (71.7%) samples yielded positive reactions in BB whereas, 50 (64.1%) samples were positive by standard fecal coliform test. A comparative study of fluorogenic and chromogenic media containing substrate beta-D glucuronide for specific detection of environmental isolates of 313 thermotolerant E. coli has been undertaken. Five fluorogenic media were used: Fluorocult MacConkey agar (MCA), Fluorocult ECD agar (ECD), Fluorocult VRB agar (VRB), Fluorocult E. coli 0157:H7 agar (ECH7) and Fluorocult Brilla Broth (BB) and Chromogenic Chromocult agar (CCA). BB and CCA were found to be highly specific and sensitive media to detect E. coli as all E. coli yielded positive reaction on them. On ECH7 and ECD agar 67.5 and 64.9 of E. coli isolates gave positive reaction, respectively. Low sensitivity was observed in case of MCA and VRB agar in detecting E. coli. The performance of BB appears to be better when compared with standard MPN procedure employing MacConkey broth/Brilliant green bile broth in detecting E. coli in drinking water.
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