PERFORMANCE OF RAPID POLYMYXIN NP TEST AMONG TWO SPECIES OF FAMILY ENTEROBACTERIACEAE

Objectives: Performing polymyxin susceptibility testing is a challenge in resource limited settings with broth microdilution as a standard method. Nordmann and Poirel introduced Rapid Polymyxin NP Test, qualitative calorimetric test for interpreting the susceptibility or resistance to colistin for Enterobacteriaceae. Due to limited data on the diagnostic accuracy of the test in central region of India, the current study was conducted to assess the diagnostic accuracy with ease of performance of Rapid polymyin NP test in comparison to the reference method, broth microdilution for Carbapenam resistant Escherichia coli and Klebsiella pneumoniae, the two prevalent species isolated across samples.

Methods: Single center tertiary care hospital based cross sectional study for a period of eight months. The Rapid polymyxin NP test and broth microdilution test was performed for 13 isolates of carbapenam resistant E.coli and 10 isolates of Klebsiella pneumoniae sub species pneumoniae, including only one isolate per patient.

Results: Rapid Polymyxin NP test showed 86.95% sensitivity and 100% specificity when compared to BMD test. Time to positivity by rapid polymyxin NP ST was 3 to 4 hrs when compared to BMD ST which was as almost 10-12hrs.

Conclusions: The specificity of 100% for the Polymyxin NP test indicates that it may be utilized as a confirmatory test. With the sensitivity as 86.95% Polymyxin NP test can be used as a very good screening test. The NPV was 40% hence whenever the test result is resistant by Polymyxin NP test one can only be 40% sure that it is a true resistant.