Clinical Validation of SensiTest Colistin, a Broth Microdilution-Based Method To Evaluate Colistin MICs

Abstract

The global spread of multidrug-resistant Gram-negative bacteria has led to the return of colistin for treating severe infections. Recently, different plasmid-mediated genes conferring resistance to this drug were described and reported worldwide. International committees (EUCAST/CLSI) reevaluated inconsistencies surrounding colistin antimicrobial susceptibility testing (AST), concluding that broth microdilution (BMD) should serve as the reference method for AST. The development of an accurate, reproducible commercial test based on BMD is therefore highly desirable. SensiTest Colistin (STC), a BMD-based compact 4-test panel containing the lyophilized antibiotic in 7 2-fold dilutions (0.25 to 16 μg/ml) was here compared with the EUCAST-CLSI standard reference method (BMD) and, for some isolates, with the automated Phoenix 100 system (PHX). A total of 353 bacterial strains were evaluated by two different laboratories; 137 isolates were resistant to colistin (19 were intrinsically resistant, 83 harbored the gene). Essential agreement (EA) between STC and BMD was obtained for 339 out of the 353 strains tested (96.0%). Overall categorical agreement was obtained for 349 out of the 353 strains analyzed (98.9%). Two major errors (MEs; 0.93%) and two very major errors (VMEs; 1.46%) were documented. STC appeared to be a simple but highly reliable test with good reproducibility even with panels stored at room temperature or at 35°C. Moreover, STC showed a good performance with strains carrying the gene, with a 98.8% EA. As the secondary endpoint of our study, VMEs for PHX were documented for 6 isolates (10%).

Mcr colistin resistance gene: a systematic review of current diagnostics and detection methods

“…The MICRONAUT‐S system was shown to have the same EA as Sensititre, albeit it had lower CA (89%) and higher ME (15.38%) and VME (5.56%) (Table )(Matuschek et al., ). It can be observed from Table that Vitek had the poorest sensitivity (42.9%) to mcr‐1 producers and highest VME (36%) among all the commercial systems, which has also been confirmed by BioMerieux (Carretto et al., ). Moreover, it has been already reported that the Vitek 2 has poor sensitivity in detecting heteroresistance (Jayol, Nordmann, Brink, et al., ; Jayol, Nordmann, Lehours, et al., ).…”

“…The MICRONAUT MIC‐Strip (MMS) (MERLIN Diagnostika Gmbh, Bornheim, Germany), the UMIC system (Biocentric, Bandol, France), the MIC Test Strip (MTS) (Liofilchem, Roseto degli Abruzzi, Italy) and Sensitest Colistin (Liofilchem, Roseto degli Abruzzi, Italy) (Carretto et al., ) are novel commercial but manual tests (Table ). E ‐test and BMD, which are older MIC‐determining methods, were evaluated by two and single studies, respectively (Table ).…”

“…Four studies have evaluated the efficiency of automated commercial MIC‐determining systems,that is, MicroScan, Sensititre, MICRONAUT‐S, BD Phoenix (Phoenix 100 ™ ) and Vitek 2 (Table ) (Jayol, Nordmann, Brink, et al., ; Jayol, Nordmann, Lehours, et al., ; Carretto et al., ; Jayol, Nordmann, et al., ; Matuschek et al., ). The MicroScan and Sensititre are the only platforms that recorded 100% sensitivity in detecting mcr‐ producing Enterobacteriaceae, but Sensititre had higher CA (90.1%–97.8%), and lower ME (0%–11.8%) than that of MicroScan (88.2%, and 15.4%–26.9%, respectively).…”

“…Following the manufacturer's as well as EUCAST and CLSI instructions, Carretto et al. () evaluated the STC kit with 353 bacterial isolates and found it to have an EA of 96%, a CA of 98.9%, an ME of 0.92% and a VME of 1.46% (Table ). Notably, an EA of 98.8% was recorded for MCR‐1‐positive isolates.…”

“…They also found the kit to be highly stable, reliable, and reproducible even at room temperature and varying temperatures. It was found to be highly reproducible (Carretto et al., ). Further, minimum bactericidal concentration could be also determined from the STC plate by spotting 1–10 μl from the wells unto CAMHA plates.…”