PCR detection of metallo-β-lactamase gene (bla(IMP)) in gram-negative rods resistant to broad-spectrum β-lactams

We applied PCR to the rapid detection of the metallo-β-lactamase gene, bla(IMP) in clinically isolated gram-negative rods. A total of 54 high-level ceftazidime-resistant strains (MICs, > 128 μg/ml) were subjected to PCR analyses with the bla(IMP)-specific primers, since the bla(IMP)-bearing clinical isolates tested in our previous study always demonstrated high- level resistance to ceftazidime. Twenty-two bla(IMP)-positive strains including 9 Pseudomonas aeruginosa, 9 Serratia marcescens, 2 Alcaligenes xylosoxidans, 1 Pseudomonas putida, and 1 Klebsiella pneumoniae strains were newly identified from 18 different hospitals in Japan. These strains were mostly isolated from urine samples and showed high-level resistance to almost every cephem, while their levels of resistance to carbapenems were diverse. The PCR analyses with novel integrase gene-specific (intI3) and acc(6')-Ib gene-specific primers suggested that the integron structure found in a large plasmid harbored by S. marcescens AK9373 was also well conserved among bla(IMP)-positive strains. These results imply that the bla(IMP) gene cassettes have been dispersing into various gram-negative rods with the help of the newly identified integron element. Thus, the PCR-aided rapid detection will be helpful for the early recognition of emerging bla(IMP)-positive clinical isolates which demonstrate consistent resistance to β-lactams.