Abstract:
Background: Global carbapenem resistance is causing significant treatment failures and raising
mortality rates. However, there is limited local data on the prevalence of carbapenemase
production among multidrug-resistant (MDR) gram-negative bacteria.
Objectives: To determine the prevalence of carbapenem resistance and production of
carbapenemase using phenotypic methods of Modified Hodge Test (MHT), Carbapenem
inactivation method (CIM) and modified carbapenem inactivation method (mCIM) among MDR
gram-negative bacteria isolated at teaching hospital Karapitiya (THK) and to compare the
performance of the MHT, CIM with mCIM, which is the reference standard given in the Clinical
Laboratory Standard Institute (CLSI) guidelines
Methods: A cross-sectional study was conducted from August to October 2023. MDR gram
negatives were obtained from the Microbiology Laboratory at THK following identification using
routine microbiological methods. Consecutive samples from the same patient were excluded.
Their carbapenem resistance was tested using the disk diffusion method with meropenem (10 μg),
ertapenem (10 μg) and imipenem (10 μg). Carbapenemase production was detected using MHT,
CIM and mCIM.
Results: Of all 129 MDR gram-negative bacteria, found during the study period, 65.1% (n=84)
were resistant to carbapenem and 2.3% (n=3) showed intermediate resistance. Carbapenem
resistance among Acinetobacter spp. and Pseudomonas spp. were 100% whereas that was 53.4%
among Enterobacteriaceae. Prevalence of carbapenemase production by mCIM, MHT and CIM
were 46.4% (39/84), 34.5% (29/84) and 32.1% (27/84), respectively. Validity of tests were
assessed with 95% confidence interval. Sensitivity and specificity of MHT compared to mCIM
was 59.0% (43.5%-74.4%) and 87.2% (77.7%-96.8%), the sensitivity and specificity of CIM
compared to mCIM was 46.2% (30.5%-61.8%) and 80.9% (69.6%-92.1%). Positive predictive
value of MHT and CIM was 79.3% (64.6%-93.8%) and 66.7% (48.9%-84.4%), respectively when
compared to mCIM. Negative predictive value of MHT and CIM were 71.9% (60.3%-83.6%) and
64.4% (53.2%-76.6%), respectively when compared to mCIM.
Conclusions: Urgent attempts are required to combat carbapenem resistance in Sri Lanka. In
resource-limited clinical laboratories without genotypic detection methods, mCIM is the preferred
method for detecting carbapenemase synthesis.
