Abstract
OBJECTIVES: To evaluate four phenotypic tests for the detection of metallo-beta-lactamase (MBL) production in Pseudomonas aeruginosa in a low MBL prevalence setting. METHODS: Sixty clinical isolates of P. aeruginosa resistant to imipenem and/or meropenem and seven MBL-positive control strains were examined by: (i) MBL Etest; (ii) combined imipenem discs supplemented with EDTA (IPM-EDTA); (iii) beta-lactam discs on dipicolinic acid plates (DF-DIPI); and (iv) the Cica-beta test. Spectrophotometric analysis of crude cell extracts for imipenem hydrolysis along with consensus PCRs for bla(VIM) and bla(IMP) was used as reference methods. RESULTS: Two clinical isolates (3\%) were MBL-positive. The MBL Etest and IPM-EDTA test scored positive for all MBL-positive isolates, but showed specificities of 86\% and 91\%, and positive predictive values (PPVs) of only 20\% and 29\%, respectively. Adding resistance to ceftazidime (MIC \textgreater8 mg/L) as a criterion for MBL testing would reduce the number of isolates to be screened by 50\% and increase the PPVs of the MBL Etest and IMP-EDTA test to 29\% and 40\%, respectively. The Cica-beta test correctly identified all MBL-negative isolates, but misidentified one MBL-positive clinical isolate as an extended-spectrum beta-lactamase (ESBL)-producer and one as inconclusive (producing multiple beta-lactamases). No reliable breakpoints could be defined for the DF-DIPI test due to overlapping inhibition zone diameters for MBL-positive and -negative isolates. CONCLUSIONS: None of the phenotypic tests were optimal due to low sensitivity or specificity, resulting in low PPVs. Including ceftazidime resistance to the MBL-screening criteria would significantly improve the performance of the MBL Etest and IPM-EDTA disc test.
- aeruginosa,
- and
- bacterial
- bacterial,
- chain
- humans,
- imipenem,
- infections,
- microbial
- of
- polymerase
- predictive
- proteins,
- pseudomonas
- reaction,
- resistance,
- sensitivity
- specificity,
- spectrophotometry
- tests,
- value
- {beta-lactamases,}
- {beta-lactam}
- {dna,}
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