Spread of a "Pseudomonas-specific" beta-lactamase to plasmids of enterobacteria

Eleven isolates including Escherichia coli, Salmonella enteritidis, and Shigella sonnei, obtained in Brazil, Hong Kong, Indonesia, Thailand, and the United States, were found to produce beta-lactamase of the PSE-1 type, which was previously considered to be Pseudomonas specific. The enterobacterial strains produced a beta-lactamase with the same isoelectric point, immunological reactions, and substrate profile as those of the prototype PSE-1 enzyme determined by Pseudomonas plasmid RPL11. The producer strains were resistant to multiple antibiotics, and all contained plasmids, ranging in size from 37 x 10(6) to 130 x 10(6), that belonged to at last six incompatibility groups. Plasmids of IncH2 and IncFIme were shown to contain 8 x 10(6)-molecular-weight transposons Tn1401 and Tn1402 that encoded PSE-1 beta-lactamase production, resistance to streptomycin and spectinomycin via AAD(3"), and resistance to sulfonamide. PSE-1 beta-lactamase was not Pseudomonas specific and appeared to have spread among plasmids found in enterobacteria by transposition.