SCREENING OF PLASMIDS FROM WASTE-WATER BACTERIA

Research on the plasmids in wastewater bacteria was carried out. From the results of comparative studies on plasmid screening methods, the method of Kado and Liu was considered to be most suitable for detecting plasmids in wastewater bacteria among the five methods tested. Forty five antibiotic resistant bacteria and 10 dominant bacteria were isolated from wastewater samples, and their plasmid contents were examined by using Kado and Liu's method with minor modifications. In total, 31 plasmids were detected in 14 of 45 antibiotic resistant strains, with 10 strains carrying multiple (2-4) plasmids. Their sizes were in the range of 1.8-168 kb, and plasmids with sizes 20-30 kb and less than 10 kb were dominant (29 and 26%, respectively). Several large plasmids detected in antibiotic resistant strains seem to be conjugative. On the other hand, 4 of 10 dominant strains had multiple (4-9) plasmids, and 63% of them were less than 10 kb. So it appeared that plasmids were ubiquitous in wastewater bacterial populations.