CARBA NP - EVALUATING ITS PERFORMANCE USING THREE DIFFERENT INDICATORS

Abstract

INTRODUCTION: The greatest threat to antimicrobial treatment of infections caused by Gram-negative bacteria is the production of
carbapenemases. The CLSI has recommended CarbaNP (CNP) test based on the principle of acidimetry for the detection of these carbapenemases.
AIMS & OBJECTIVES: To evaluate the performance of CNP test for the detection of carbapenemases using three different indicators – phenol
red, cresol red and bromothymol blue.
METHODOLOGY: The CarbaNP test was done according to CLSI guidelines using three different indicators 0.05% phenol red / 0.05% cresol
red / 0.05% bromothymol blue on 72 well characterised E. coli isolates.
RESULTS: CarbaNP test with phenol red as the indicator could detect a total of 52/53 MBL producing E coli. The sensitivity of CNP test with
cresol red and bromothymol blue was 92.5% and 96.2% respectively. The specificity was 100% with all the three indicators.
CONCLUSION: The CLSI described CNP test using phenol red was more sensitive for detection of carbapenemases. But faster results were
obtained using cresol red, although weak carbapenemase activity could be better visualized using bromothymol blue indicator.