Phenotypic Detection of Carbapenemase in PseudomonasaeruginosabyCarbapenem DiskswithDipiclonic Acid and Aminophenylboronic Acid

Abstract

The spread of carbapenemase-producing Pseudo-monas has become a global threat. The emergence of resistance to carbapenems makes the treatment for infections caused by these carbapenem-resistant strains very limited. The main mechanism of resistance in carbapenems is the production of carbapenemase by gramnegative bacteria.Different types of carbapenemases have been reported, such as KPC and MBLs. Rapid and accurate detection of carbapenemase-producing P.aeruginosa is considered essential to implement appropriate treatment and infection control measures. The aim of this work is to establish a phenotypic screening test for identification of MBLs and KPC among P.aeruginosa isolates using carbapenem disks supplemented withdipiclonic acid (DPA) and aminophenylboronic acid (APB). This study was done onfifty clinical isolates of carbapenem resistantP.aeruginosa recovered from various clinical specimens referred to the Microbiology Laboratory of Ain Shams University Hospitals for routine culture and sensitivity in the period from March 2014 to October 2014. All isolates were subjected to CDT using carbapenem disks supplemented with DPA and APB for detection of MBLs and KPC respectively. Real time PCR was done for detection of blaIMP and blaKPC genes. Combined disk test (CDT) using imipenem and meropenem with DPA was positive in 10 specimens (20%) and was negative in 40 specimens (80%). BlaIMP gene was detected by PCR in 13 specimens (26%) and was negative in 37 specimens (74%). CDT using meropenem with APB was positive in 11 specimens (22%) and was negative in 39 specimens (78%), while CDT using imipenem with APB was positive in 9 specimens (18%) and was negative in 41 specimens (82%). BlaKPC gene was detected in 15 specimens (30%) and was negative in 35 specimens (70%). The CDT using MEM and IPM with DPA for detection of MBLs both showed 100% specificity, 76.9% sensitivity, and 94% accuracy. While CDT using MEM/APB for detection of KPC showed 66.7% sensitivity, 97.1% specificity, and 88% accuracy and CDT using IPM/APB showed 53.3% sensitivity, 97.1% specificity, and 84% accuracy.