The differential expression of genes for the PSE-4 beta-lactamase in Pseudomonas aeruginosa and the Enterobacteriaceae.

The PSE-4 beta-lactamase has been identified, for the first time, in two non-pseudomonal strains. The gene in Klebsiella pneumoniae 241 (dal1) was located on a plasmid (pUK700) and was freely transferable to other enterobacterial strains and Pseudomonas aeruginosa. On the other hand, the gene in Enterobacter cloacae A113 (dal2) could only be transferred in the presence of a mobilizing plasmid. When both these genes were transferred within the Enterobacteriaceae, the beta-lactamase produced was slightly different from the prototype 'Dalgleish' PSE-4 enzyme. However, when dal1 and dal2 were transferred to P. aeruginosa the enzyme expressed was identical to this prototype enzyme. In addition, both these genes expressed higher levels of PSE-4 beta-lactamase production in P. aeruginosa than found in the Enterobacteriaceae. Thus it appears that the biochemical properties of the PSE-4 gene products from dal1 and dal2 are host-modified.