Direct screening of the IMP-1 metallo-β-lactamase gene (bla_IMP) from urine samples by polymerase chain reaction

Background: As Gram-negative bacterial isolates producing plasmid-mediated IMP-1 metallo-β-lactamase usually demonstrate resistance to various broad-spectrum β-lactams, including cephamycins and carbapenems, transmission and proliferation of these microorganisms in clinical settings could become a clinical threat in the near future. According to previous studies by the same authors, IMP-1-producing strains are usually isolated from urine samples. Therefore, in this study, a polymerase chain reaction (PCR) was applied for direct screening of the IMP-1 metallo-β-lactamase gene in urine samples. Method: Urine samples were collected from 273 inpatients to whom various broad-spectrum β-lactams, including carbapenems, had been administered in 57 hospitals in 1997. DNA templates for PCR analyses were prepared directly from 19 urine samples from whichSerratia marcescens strains demonstrating high-level resistance (minimal inhibitory concentration > 128 μg/mL) to both ceftazidime and cefoperazone-sulbactam were later isolated. Results: The IMP-1 metallo-β-lactamase gene (bla_IMF)-specific 578 bp fragments were able to be IMR amplified successfully in eight of the 19 samples. In the seven strains isolated from the eight samples, the presence of blaIMP was also detected by a DNA hybridization analysis. The lower limit of the PCR method was determined as 1 × 10² CFU of bla_IMP-bearing bacterial cells per 1 mL of urine sample. No false positive result was found. Conclusion: The PCR-aided direct screening of bla_IMP is applicable to early recognition of IMP-1-producing bacteria in urine samples. This method would help to prevent nosocomial and inter-hospital transmission of this kind of hazardous bacteria, as well as the advancement of rigorous infection control.