Secondary in-hospital epidemiological investigation after an outbreak of Pseudomonas aeruginosa ST357

The secondary in-hospital epidemiological investigation for drug-resistant Pseudomonas aeruginosa infections was conducted to evaluate the in-hospital situation and identify any associations between exoenzyme genotypes and other genotypes and antimicrobial resistance characteristics, at the University Hospital in Kyoto, Japan, following a reported outbreak of antimicrobial-resistant P. aeruginosa ST357 between 2005 and 2014. Twelve of the 546 P. aeruginosa isolates collected during the follow-up period were resistant to more than two classes of antimicrobials. All isolates were resistant to fluoroquinolones and 8 (66.7%) showed carbapenem resistance. None of the isolates fulfilled the clinical criteria for multidrug-resistant P. aeruginosa. All isolates were metallo-β-lactamase test-negative. Among five exoS (−)exoU (+) isolates, three possessing a class 1 integron with gene cassette aadB + cmlA6 were classified as ST357, and one isolate containing a class 1 integron with aacA31 was ST235. Collectively, the second survey results confirm that the initial outbreak is currently undergoing convergence. By combining data from the first and second surveys, we showed that prevalent STs such as ST357 and ST235 are associated with fluoroquinolone resistance, class 1 integron-associated resistance to β-lactams and aminoglycosides, and cytotoxic exoU (+) genotypes. With the current worldwide spread of ST357 and ST235 isolates, it is important to evaluate epidemiological trends for high-risk P. aeruginosa isolates by continuous hospital monitoring.