EVALUATION OF A SCREENING TEST FOR POLYMYXIN RESISTANCE

The bacterial resistance is a serious global public health issue, with high prevalence of Gram-negative bacilli (GNB) infections. The extensive use of carbapenem in treatment of GNB infections has contributed to the emergence and spread of resistance mechanisms in hospital environment, restricting the therapeutic options to difficult-to-handle antibiotics such as polymyxins B and E (colistin). Although facing many limitations, the broth microdilution method susceptibility test is considered a benchmark method for polymyxins and, in general, alternative commercial methodologies for detection of resistance, as the automated ones or concentration gradient tapes, do not show high correlation with the benchmark method. Thus, the search for suitable alternatives is of great interest. This study sought to evaluate a screening test for detection of resistance to polymyxins by comparing it with broth microdilution method for polymyxin B and colistin. The VITEK®2(BioMérieux) automated system was also used in the colistin case. One hundred and thirty-one carbapenems resistant GBN were isolated at University Hospital of the State University of Londrina between March to June 2018 and selected for this study. Carbapenem and polymyxin results were interpreted according to sensitivity criteria of the Clinical and Laboratory Standards Institute (CLSI, 2018). Among the 131 GNB evaluated, the most frequent were 51.1% Acinetobacter spp, Klebsiella pneumoniae (32.8% of the isolates) and 14.5% Pseudomonas aeruginosa. In the analysis of susceptibility to polymyxin B, GNB which are resistant to that antimicrobial by broth microdilution method composed 17.6%, and 19.8% by the screening test, having only one strain classified as intermediate in both tests. Still for this antibiotic, when comparing broth microdilution method with the screening test, agreement was obtained of 92.4% of the results. The isolates resistant to colistin by the broth microdilution method technique were 19.8%, by the screening test 22.1% and for the automated method 19.8%. Comparing the screening test with broth microdilution method for colistin, 92.4% of the strains presented similar results. The broth microdilution method technique and the automated system obtained similar results in 94.6% of the isolates. In short, the screening test is promising, with similar results to those obtained by broth microdilution method for the analyzed samples. However, we believe that complementary studies that contemplate a greater number of samples of different species and origins are needed, in order to establish the specificity and sensitivity of this test for routine use in clinical laboratories.