Isolation of indigenous wastewater bacterial strains capable of mobilizing plasmid pBR325

Members of the family Enterobacteriaceae have been isolated from raw wastewater, identified, and characterized with respect to their plasmid content and antibiotic resistance. Several strains possessing both antibiotic resistance and high-molecular-weight plasmid(s) transferred their resistance characteristics to recipient cells during a 25 h coincubation. Eight were characterized (six Escherichia coli and two Klebsiella pneumoniae); each produced 10(2) to 10(7) transconjugants per ml by the end of the incubation period. They were also able to mobilize pBR325 from a laboratory E. coli strain into plasmid-free recipients to yield 10(2) to 10(7) transconjugants per ml. These transconjugants possessed phenotypic characteristics specified by pBR325, the R plasmid, and the chromosome of the recipient. Many transconjugants exhibited recombinational rearrangements of the acquired plasmid material.