Characterization of Acquired Beta-Lactamases and Their Genetic Support in Multidrug-Resistant Pseudomonas Aeruginosa Isolates in Taiwan: The Prevalence of Unusual Integrons

Abstract

Objectives: The present study was conducted to investigate acquired beta- 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 beta-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-beta- 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-10)-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.