Isolation of Pseudomonas aeruginosa producing OXA-4 beta-lactamase in a Japanese hospital in 1996.

One-hundred and fifty isolates of Pseudomonas aeruginosa were collected from different patients' specimens at Showa University Fujigaoka Hospital between April and August 1996. The 23 isolates resistant to piperacillin (minimum inhibitory concentration, >or=100 microg/ml) were widely distributed in the hospital wards. Using polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) and isoelectric focusing (IEF) methods, we detected OXA-4 beta-lactamase hydrolyzing penams in 4 of the resistant isolates (17%) with O-serotype E. However, no other external beta-lactamase was detected by the IEF method. The hybridization results showed that the OXA-4 genes were located in chromosome, but not in plasmid. Furthermore, the isolation rate was significantly lower than that found between 1992 and 1993 (61%; P < 0.01; chi2-test), suggesting a decreased rate of hospital infection caused by P. aeruginosa producing the OXA-4 enzyme.