Original Research Article
Year: 2019 | Month: October-December | Volume: 4 | Issue: 4 | Pages: 110-115
Colistin Susceptibility for Carbapenem Resistant Gram Negative Bacilli; Comparative Study of E-test and Vitek 2 Compact™ with Broth Microdilution
Ayushi Sharma1, Mohit Agrawal2
1Postgraduate student, 2Associate Professor,
Department of Microbiology, Mahatma Gandhi University of Medical Sciences and Technology, Jaipur
ABSTRACT
Purpose: Colistin remains part of the last line drugs used to treat multi-drug resistant Gram negative bacilli, like carbapenem resistant GNB. At present CLSI-EUCAST joint recommendations are for using Broth microdilution (BMD) as the reference method for testing colistin susceptibility. This study was undertaken to assess and compare commercially available susceptibility testing methods for MIC determination of colistin against the reference BMD.
Method: 510 CRGNB were included under the course of 6 months, from January 2019 to June 2019. Carbapenem resistance was detected by Vitek 2 Compact™ and the isolates were further processed for colistin susceptibility testing by E-test, Vitek 2 Compact™ (Biomerieux, France) and BMD.
Result: 32 (6.27%) isolates were found colistin resistant by the reference method BMD. Klebsiella pneumoniae (43.75%) was the predominantly isolated organism, followed by Pseudomonas aeruginosa (31.25%), Enterobacter cloacae complex (12.5%), Acinetobacter spp.(6%), E.coli (3%) and Enterobacter aerogenes (3%). Rates of essential agreement (EA) for E-test and Vitek 2 Compact™ were 66% and 85% respectively. Categorical agreement (CA) was found to be 73% or E-test and 96% for Vitek 2 Compact™. There was no very major error (VME) for Vitek 2 Compact™. E-test presented with 33% VME. While there was no major error (ME) for E-test, 4% of ME were noted for Vitek 2 Compact™.
Conclusion: The findings of this study showed substantial discordance between colistin susceptibility testing methods, with the overall reliability E-test being poor for MIC determination and reliability of Vitek 2 Compact™ was considered moderate when BMD was taken as the reference method.
Key words: Colistin, Carbapenem, Gram negative bacilli, Broth microdilution, E-test