Evaluation of six commercial products for colistin susceptibility testing in Enterobacterales

Abstract

Objectives: The recommended technique for colistin susceptibility testing by both EUCAST and CLSI is broth microdilution (BMD). However, many routine laboratories still use other methods such as gradient strips or semi-automated systems. The objective of this study was to compare six of the most widespread commercial products for colistin susceptibility testing in Europe with in-house prepared BMD. Methods: A collection of 325 carbapenemase-producing Enterobacterales was tested for colistin susceptibility with three semi-automated systems (Vitek 2, BD Phoenix, MicroScan WalkAway), one gradient-strip test (Etest®) and two commercial BMD products (MICRONAUT-S, TREK Sensititre). BMD, in-house prepared according to ISO standard 20776-1, served as reference. Results: The MICRONAUT-S BMD performed best with only one false-resistant (major error, ME) and four false-susceptible (very major error, VME) results while the TREK BMD performed poorer with 16 ME and seven VME. The semi-automated systems Vitek 2 and Phoenix performed poorly with 31 and 26 VME, respectively. The WalkAway semi-automated system showed 16 and 13 false results, depending on the inoculation method. The Etest® showed six ME and 10 VME. Conclusions: This study shows that colistin susceptibility testing remains a challenging task for laboratories. It emphasizes the need for selecting the most reliable test method to advocate proper treatment and shows that critical evaluation and precautious usage of colistin susceptibility testing results is constantly required.

Evaluation of Calcium-Enhanced Media for Colistin Susceptibility Testing by Gradient Agar Diffusion and Broth Microdilution

“…Gradient diffusion is generally regarded as an inaccurate method for colistin susceptibility testing. However, historical data have been highly variable, ranging from excellent agreement for Enterobacterales (16)(17)(18) to either moderate (9,(19)(20)(21) or high (2,8,11,12,22,23) rates of errors, particularly VMEs. This variability is likely attributable to multiple factors, in particular the diversity of isolates evaluated in each study, as represented by MIC distributions, species and strain types, and mechanisms of resistance, including heteroresistance.…”

The accuracy of four commercial broth microdilution tests in the determination of the minimum inhibitory concentration of colistin

“…Due to the restriction implemented by EUCAST and CLSI regarding AST for colistin, routine laboratories are now forced to introduce this laborious technique in their daily routine setting. Fortunately, several companies responded to this challenge, by bringing an easy-to use AST for colistin based on BMD method to the market [9,10]. So far only a few studies have been published regarding the performance of commercial BMD colistin.…”

Molecular epidemiology of mcr gene group

“…На фоне многочисленных публикаций, указывающих на низкую согласованность результатов оценки чувстви тельности различными методами (дискодиффузионным, методами градиентной диффузии, методами разведе ний) [81], в 2016 г. был принят совместный документ американского Института клинических и лаборатор ных стандартов (CLSI) и Европейский комитет по опре делению чувствительности к антимикробным препара там (EUCAST), в котором были приняты общие подходы к интерпретации результатов определения чувствитель ности к колистину для Enterobacterales, A. baumannii и P. aeruginosa [105], а два года спустя был опублико ван еще один документ, который внес окончательную ясность в перспективы клинического применения ко листина [82]. В соответствии с данным документом, штаммы, имеющие МПК колистина ≥ 4 мкг/мл, явля ются устойчивыми и относятся к категории «R», изоляты с МПК колистина < 2мкг/мл должны быть отнесены к категории «I» (increased exposure -чувствительные, до зозависимые), что отражено и в последней редакции клинических интерпретационных критериев CLSI [83].…”