Comparing Quantitative and Qualitative Methods for Detecting the In Vitro Activity of Colistin against Different Gram-Negative Bacilli

Shams N,Albukhati K,Zughaie Sm,Eltai No,Alsowaidi K,Moulana N,Riahi M,Alhiraky H

doi:10.26420/jbacteriolmycol.2021.1181

Abstract

The surge in the prevalence of Multidrug-Resistant (MDR) Gram-negative bacterial infections with limited treatment led to colistin reusing to treat MDR infections. This study aimed to determine economical, simple, and reliable colistin susceptibility testing methods as an alternative to the microdilution technique. We compared seven colistin susceptibility testing methods, including quantitative and qualitative, namely: Disk diffusion, E-test, ComASPTM SensiTest Colistin, Colistin broth disk elution, and colistin agar test CHROMagarTM COL-APSE, and BD Phoenix ID/AST automated identification and susceptibility testing system to the gold standard Broth Microdilution (BMD). Whole-genome sequencing was performed on all isolates to determine if the genetic resistant factors affect the phenotypic profile of the colistin resistance. Our results revealed that disk diffusion is still an ineffective method for measuring colistin susceptibility in Gram-negative Bacilli with the highest major error (31.75%), the lowest Kappa 0 (0%), and categorical agreement (68.25%) values. Phoenix, and CompASPTM SensiTest colistin methods have remained superior in reproducibility, sturdiness, and simplicity of use, similar to the currently recommended broth microdilution procedure; with high sensitivity of 95.56%, and 97.73%, specificity of 95.24, and 100%, and Kappa values of 0.89 and 0.95, respectively. This study revealed that Phoenix, and ComASPTM SensiTest colistin methods are recommended for routine microbiology laboratories with a large workload.

Highlights

Colistin is a cationic polypeptide antibiotic that belongs to the family polymyxin, including polymyxin B and polymyxin E
43 (68%) of the studied Gram-negative isolates were resistant to colistin by gold standard Broth Microdilution (BMD) with resistance detected in 13 (72%) of K. pneumoniae, 2 (100%) P. aeruginosa, and 28 (65%) E. coli isolates (Table 1)
DNA was sent to BGI Genomics Co., Ltd., China, for whole-genome sequencing

Summary

Introduction

Colistin is a cationic polypeptide antibiotic that belongs to the family polymyxin, including polymyxin B and polymyxin E (colistin) It is the last resort for treating multidrug resistance Gramnegative Bacilli (MDR-GNB), mainly against Escherichia coli (E. coli), Klebsiella pneumoniae (K. pneumoniae), and Pseudomonas aeruginosa (P. aeruginosa) [1,2]. It is synthesized naturally by Paenibacillus polymyxa and is rapidly bactericidal to Gram-negative bacteria. Its central role is to inhibit cell membrane function by increasing its permeability to absorb polymyxins substances. Several MDR-GNB bacteria developed their defense mechanisms against colistin This resistance development could be either chromosomal or plasmid-mediated. The cell membrane permeability will be reduced, and polymyxin binding will be suppressed [1,5,6,7]

Objectives

Methods

Results

Discussion

Conclusion