Characterization of acquired β-lactamases and their genetic support in multidrug-resistant Pseudomonas aeruginosa isolates in Taiwan: The prevalence of unusual integrons

Objectives: The present study was conducted to investigate acquired β-lactamases and their genetic support in 26 Pseudomonas aeruginosa isolates that were resistant to nearly all antipseudomonal drugs from six medical centres in Taiwan. Methods: Acquired β-lactamases and their genetic support were determined by PCR-based strategies. Results: Four and 16 of the 26 isolates were found to produce VIM-2 and VIM-3 metallo-β-lactamases (MBLs), respectively, and 1, 1 and 2 isolates produced OXA-17, OXA-10 and PSE-1, respectively. These bla genes are all in class 1 integrons that are probably chromosomally located. The bla_VIM-3-containing integron, with a deletion between int1 and the bla VIM-3 structural gene, has six gene cassettes, bla VIM-3, a probable fosfomycin resistance determinant, aacA4, aacA4, aadB and aacA4. The bla_VIM-2-containing integron, without detectable 5′-conserved segment, contains four genes cassettes (aacA7-bla_VIM-2-dhfr-aacA5) and is ended by tniC. The bla_OXA-102-containing integron includes a catB3 cassette and a fused gene cassette, which is made up of bla_OXA-17 and a novel streptomycin-spectinomycin gene, designated aadA15. The bla_OXA-17-containing integron has three gene cassettes (aacA4-catB2-bla_OXA-17) but the 59-base element of the bla OXA-17 cassette is interrupted by a putative transposase gene. The bla_PSE-1-containing integron has three gene cassettes, aacA4, an aadA3 -related gene designated aadA3b and bla_PSE-1. PFGE revealed genetic diversity among the multidrug-resistant isolates from different hospitals. Conclusions: This study demonstrated the high prevalence of VIM-type MBLs and the presence of unusual bla -encoding integrons in multidrug-resistant P. aeruginosa isolates in Taiwan. The spread of bla_VIM-2-related genes by horizontal transfer might have occurred.