Isolation and characterization of arsenic resistant bacteria from wastewater

The present study proposed the isolation of arsenic resistant bacteria from wastewater. Only three bacterial isolates (MNZ1, MNZ4 and MNZ6) were able to grow in high concentrations of arsenic. The minimum inhibitory concentrations of arsenic against MNZ1, MNZ4 and MNZ6 were 300 mg/L, 300 mg/L and 370 mg/L respectively. The isolated strains showed maximum growth at 37 ºC and at 7.0 pH in control but in arsenite stress Luria Bertani broth the bacterial growth is lower than control. All strains were arsenite oxidizing. All strains were biochemically characterized and ribotyping (16S rRNA) was done for the purpose of identification which confirmed that MNZ1 was homologous to Enterobacter sp. while MNZ4 and MNZ6 showed their maximum homology with Klebsiella pneumoniae. The protein profiling of these strains showed in arsenic stressed and non stressed conditions, so no bands of induced proteins appeared in stressed conditions. The bacterial isolates can be exploited for bioremediation of arsenic containing wastes, since they seem to have the potential to oxidize the arsenite (more toxic) into arsenate (less toxic) form.

Aetiology of shigellosis in northern Pakistan.

People of northern Pakistan face health hazards because of poor sanitation practices. Bacterial gastrointestinal infections are very common, and sometimes outbreaks occur. The present study was aimed at evaluating and analyzing infestation of Shigella spp. in patients with suspected gastroenteritis and ascertaining the status of antibiotic therapy. Five hundred and eighty-five faecal samples of patients with suspected gastroenteritis, referred to the District Headquarter Hospital Gilgit, were investigated for common enteropathogenic bacteria from July 1997 to September 1999. Seventy-seven (13.2%) of the faecal specimens were infected with different strains of Shigella spp., 61% of which were Shigella dysenteriae, 15.6% were S. flexneri, and 23.4% were Shigella sp. All Shigella strains were sensitive to ceftriaxone, cefotaxime, ciprofloxacin, and enoxacin. Sixty-one percent of the strains were resistant to both ampicillin and chloramphenicol, and 3.9% to ampicillin and nalidixic acid, while 10.4% were resistant to ampicillin alone and 14.3% to chloramphenicol only. Only 10.4% of the strains were sensitive to all the antibiotics tested. Sixty strains of Shigella spp. were processed for isolation of plasmids, and 58 (97%) of these antibiotic-resistant bacteria harboured at least one plasmid. The number of plasmids varied from 1 to 9. Escherichia coli C600 were transformed with the isolated plasmids. Transformants, containing 23-kb plasmid, resisted growth in media containing antibiotics, thereby indicating that antibiotic resistance is plasmid-borne. Based on the findings of the study, it is concluded that the infestation of Shigella spp. is high in northern Pakistan, the aetiological agents are highly resistant to chloramphenicol and ampicillin, and the antibiotic resistance is mediated by the 23-kb plasmid.