Abstract
A homemade and culture-based test, relying on the visual detection of the reduction of the resazurin reagent (a cell viability indicator), has been developed for the rapid detection of polymyxin resistance in Acinetobacter baumannii. Here, we evaluated the industrial version of this test, the RapidResa Polymyxin Acinetobacter NP® test (Liofilchem, Italy). A well-characterized panel of 68 clinical A. baumannii strains (36 polymyxin-susceptible, 26 polymyxin-resistant A. baumannii, and 6 colistin-heteroresistant isolates) of worldwide origin was tested. All the colistin-susceptible A. baumannii isolates gave negative results according to the RapidResa Polymyxin Acinetobacter NP® test, except for a single isolate that gave a false-positive result. Out of the 26 colistin-resistant A. baumannii strains, 25 were correctly identified as colistin resistant using the RapidResa Polymyxin Acinetobacter NP® test. Only a single colistin-resistant A. baumannii strain gave a false-negative result. Additionally, the six colistin-heteroresistant isolates tested gave positive results. Altogether, the sensitivity and the specificity of the test were found to be 96% and 97%, respectively. The turn-around-time of this easy-to-perform test was 3-4h, which showed excellent reliability for identification of polymyxin resistance in A. baumannii. The RapidResa Polymyxin Acinetobacter NP® test allows a rapid differentiation between polymyxin-susceptible and -resistant A. baumannii isolates, which may contribute to optimization of the use of polymyxins for treating infections due to multidrug-resistant A. baumannii.
Highlights
Multidrug resistance in Acinetobacter baumannii is becoming a source of major concern worldwide [1]
36 colistin-susceptible A. baumannii isolates gave negative results according to the RapidResa
Out of the 26 colistin-resistant A. baumannii strains, 25 strains were correctly identified as colistin resistant using the RapidResa Polymyxin
Summary
Multidrug resistance in Acinetobacter baumannii is becoming a source of major concern worldwide [1]. This opportunistic pathogen is intrinsically resistant to many antibiotic agents and can acquire resistance to all antibiotics, virtually. Very high percentages of carbapenem-resistant A. baumannii have been observed worldwide during the past decade [1,5]. Polymyxins, such as colistin, are considered as last resort antibiotics for the treatment of infections with carbapenem-resistant A. baumannii (CRAB) [6,7,8]. Choice of a polymyxin-based treatment is mainly based on the result of susceptibility testing performed through different techniques
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