Journal of Clinical Microbiology
Journal of Clinical Microbiology
5 years ago

Evaluation of the Rapid Polymyxin NP Test for Polymyxin B Resistance Detection Using Enterobacter cloacae and Enterobacter aerogenes Isolates.

Pankey G, Ashcraft D, Sibley D, Simar S
Background: Polymyxin resistance is an increasing problem worldwide. Currently, determining susceptibility to polymyxins is problematic and lengthy. Polymyxins diffuse poorly into agar, potentially giving inaccurate disk diffusion and Etest results. A rapid screening test (2 h) for detection of polymyxin-resistance in Enterobacteriaceae, developed by Nordmann and Poirel (Rapid Polymyxin NP Test, 2016), detects glucose metabolization in the presence of polymyxins E and B via pH-induced color change. Sensitivity/specificity were 99.3%/95.4%, respectively, with results obtained in ≤2 h. Our goal was to evaluate this test using polymyxin B (PB) against larger numbers of EnterobacterMethods: 143 non-duplicate Enterobacter isolates (102 E. cloacae complex, 41 E. aerogenes) were tested, including 136 collected from Ochsner Health System patients from March-May 2016 and 7 previously determined PB-resistant E. cloacae isolates from JMI Laboratories. MICs were determined via broth microdilution. For the rapid polymyxin NP test, a color change from orange to yellow was positive; a weak/no color change, negative after 4 h.Results: 25/143 Enterobacter isolates were PB-resistant by broth microdilution (MIC >2μg/mL), including all 7 JMI isolates. Of these 25, 7 were positive by the rapid polymyxin NP test (included 3/7 JMI isolates). All 118 isolates PB-susceptible by broth microdilution were NP test negative. Sensitivity/specificity for the rapid polymyxin NP test were 25%/100%, respectively, compared to broth microdilution.Conclusions: While the rapid polymyxin NP test is a much faster method (2-4 h) for polymyxin-resistance determination compared with broth microdilution (16-20 h), our study indicates that it may be subject to limitations when testing Enterobacter.

Publisher URL: https://www.ncbi.nlm.nih.gov/pubmed/28747375

DOI: PubMed:28747375

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