Rapid detection of polymyxin resistance among carbapenem-resistant enterobacteriaceae

Abstract

Background Colistin is used currently as a last-line antibiotic for the treatment of infections caused by carbapenem-resistant Enterobacteriaceae (CRE). For colistin-susceptibility testing, the conventional methods are not reliable, and the standard broth microdilution (BMD) method is both laborious and time consuming. Therefore, there is an urgent need for a rapid diagnostic technique for identification of colistin resistance. Aim The aim was to report the prevalence of CRE among hospitalized patients, to evaluate the performance of the rapid polymyxin Nordmann/Poirel (NP) test for detection of polymyxin resistance among CRE, and to detect the mcr-1 gene among these isolates. Patients and methods A total of 300 samples were included. CRE isolates were isolated and subjected to BMD test, disk diffusion test, E-test, and rapid polymyxin NP test to detect colistin resistance. In addition, PCR assay was done to detect mcr-1 gene. Results Out of 300 different clinical samples, 132 Enterobacteriaceae isolates were obtained. The prevalence of CRE was 41.7% (55/132). The prevalence of colistin resistance among CRE isolates was 7.3% (4/55). Of the four colistin resistant isolates detected by the standard BMD, disk diffusion test and E-test detected 2 and 3 isolates as colistin resistant, respectively, giving low sensitivity (50 and 75%, respectively) and unacceptably high rates of very major errors (3.6 and 1.8%, respectively), whereas all four isolates were recorded as colistin-unsusceptible by the rapid polymyxin NP test, giving 100% sensitivity and specificity, with no very major errors. Only one isolate was detected as mcr-1 positive by PCR assay. Conclusion There is a high prevalence of CRE. Rapid polymyxin NP test is an accurate and rapid method for detection of colistin resistance. This research confirms the alarming spread of the plasmid-mediated mcr-1 gene among CRE.