Assessment of Colistin Susceptibility among Carbapenem-Resistant Clinical Isolates

Ajlan, Soma Elsayed; Elmahdy, Esraa E.; Sleem, Asmaa S.

doi:10.21608/ejmm.2022.252506

Assessment of Colistin Susceptibility among Carbapenem-Resistant Clinical Isolates

Document Type : New and original researches in the field of Microbiology.

Authors

¹ mostafa kamel street , elbtanoon, shebin elkom,menoufia Egypt

² Medical Microbiology and Immunology Department, Faculty of Medicine, Menoufia University, Egypt

10.21608/ejmm.2022.252506

Abstract

Background: Colistin is the last treatment option for infections caused by carbapenem resistant Gram-negative bacilli (CRGNB). The increasing spread of chromosomally encoded and plasmid-mediated colistin resistance made colistin susceptibility assessment a necessity. Objectives: Assessment of colistin susceptibility in CRGNB by broth micro dilution method (BMD), as the standard method and colistin broth disk elution method (CBDE), as a substitute procedure. Genotypic determination of plasmid mediated colistin resistance (mcr) genes as also done. Methodology: CRGNB were collected and identified by conventional methods. Testing carbapenemase production by modified Carbapenem Inactivation Method (mCIM) and colistin susceptibility (by BMD and CBDE) were done and results were interpreted regarding CLSI (2022) guidelines followed by genotypic detection of mcr-1, -2, -3, -4, and -5 genes by multiplex PCR. Results: 155 out of 308 GNB (50.3%) were carbapenem resistant. Among them, 129 (83.2%) isolates were carbapenemase positive by mCIM. Colistin susceptibility testing by BMD revealed 43 out of 155 CRGNB isolates (27.7%) were colistin resistant. Sensitivity, Specificity, PPV, NPV and Accuracy of CBDE were 99.09%, 93.33%, 97.32% 97.67%, 97.42% respectively with almost perfect agreement with BMD. By PCR, only 3 CRGNB isolates (6.98%) carried mcr-1 while other mcr genes were not detected at all. Conclusion: Colistin resistance rate among CRGNB is concerning, causing serious and even deadly infections so prospective surveillance is essential. Broth disk elusion method is a simple, non-expensive reliable option to test colistin susceptibility.

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