Abstract:
Background: Rapid and accurate identification of carbapenem resistance is a need, to reduce the
burden of emergence and spread of carbapenem resistant Gram-negative bacteria (CR-GNB).
Objective: To compare the carbapenem susceptibility results by Clinical Laboratory Standard
Institute disk diffusion method (DDM) and Minimum Inhibitory Concentration (MIC) by BD
PheonixTM automated system (PAS)
Method: A descriptive cross-sectional study was conducted from January to December 2023 in
University Hospital Kotelawala Defence University and Apeksha hospital to identify CR-GNB
from urine specimens received to microbiology laboratories, by both DDM and PAS. Organisms
were identified by biochemical tests and PAS while antibiotic susceptibility testing was performed
by DDM and PAS. Inter-rater agreement, Very Major Errors (VME), Major Errors (ME) and
Minor Errors (MiE) for imipenem and meropenem were calculated. Descriptive statistics were
analyzed by SPSS version 25.0.
Results: A total of 100 urinary CR-GNB were included. Organisms were identified up to the
genus level by biochemical tests where Coliforms were the commonest genus while, PAS
identified Klebsilla pneumoniae as the commonest species. AST results of meropenem and
imipenem were reported for all isolates in DDM while PAS reported for 96 isolates as the
taxonomy data of four organisms were not available. The PAS and DDM results showed a good
inter-rater agreement for both imipenem (p=0.00, k=0.70) and meropenem (p=0.00. k=0.70).
Though, VME rate of meropenem (0.00%) was acceptable, imipenem was beyond the acceptable
level (2.08%). No ME were reported in both carbapenems while, MiE were equal (2.08%).
Conclusion: Findings emaphazise the compatibility of PAS and DDM in detecting CR. Although,
vigilance is necessary for VME rate of imipenem. Further analysis should be performed to identify
specific factors like unclear assessment criteria and differing interpretations. However, species
identification by automated system will be helpful in early identification of outbreaks.
