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

Background: As Gram-negative bacterial isolates producing plasmid-mediated IMP-1 metallo-beta -lactamase usually demonstrate resistance to various bro ad-spectrum beta -lactams, including cephamycins and carbapenems, transmiss ion and proliferation of these microorganisms in clinical settings could be come 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 ap plied for direct screening of the IMP-1 metallo-beta -lactamase gene in uri ne samples. Method: Urine samples were collected from 273 inpatients to whom various br oad-spectrum beta -lactams, including carbapenems, had been administered in 57 hospitals in 1997. DNA templates for PCR analyses were prepared directl y from 19 urine samples from which Serratia marcescens strains demonstratin g high-level resistance (minimal inhibitory concentration > 128 mug/mL) to both ceftazidime and cefoperazone-sulbactam were later isolated. Results: The IMP-1 metallo-beta -lactamase gene (bla(I M P))-specific 578 b p fragments were able to be amplified successfully in eight of the 19 sampl es. In the seven strains isolated from the eight samples, the presence of b la(IMP) was also detected by a DNA hybridization analysis. The lower limit of the PCR method was determined as 1 x 10(2) CFU of bla(IMP)-bearing bacte rial 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 ear ly recognition of IMP-1-producing bacteria in urine samples. This method wo uld help to prevent nosocomial and interhospital transmission of this kind of hazardous bacteria, as well as the advancement of rigorous infection con trol.