الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 87 |  |  |
| | | from | 87 | | |
Abstract
Colistin (polymyxin E), is now the drug of choice for the treatment of infections caused by XDR Gram-negative bacteria owing to its favorable properties of rapid bacterial killing, a narrow spectrum of activity, and an associated slow development of resistance.
The aim of our work was to evaluate the performance of the rapid polymyxin Nordmann Poirel (NP) test for phenotypic detection of colistin resistance in K. pneumoniae and E.coli clinical isolates, determine the antimicrobial susceptibility pattern of those isolates, investigate the presence of colistin heteroresistance among K.pneumoniae and E. coli colistin-sensitive clinical isolates and to estimate the prevalence of plasmid mediated colistin resistance among heteroresistant and resistant clinical isolates.
A total of 70 colistin resistant isolates (65 Klebsiella pneumoniae and 5 E. coli) and 30 colistin susceptible isolates (20 Klebsiella pneumoniae and 10 E. coli) XDR were enrolled in this prospective observational study.
Regarding phenotypic colistin susceptibility in the current study, MIC of colistin was detected by the reference BMD. Colistin activity against colistin susceptible group was excellent with MIC50 of ≤0.12 μg/mL and MIC90 of ≤0.5 μg/mL. Regarding the colistin resistant group, isolates showed an MIC50 of 8 μg/mL, and MIC90 of 16 μg/mL.
In comparison to the reference BMD, the disc diffusion test showed 38% (38/100) categorical agreement for all tested isolates. The categorical agreement was 36.8% in K. pneumoniae isolates and 46.6% in E. coli isolates.
Rapid polymyxin NP test showed an excellent concordance with BMD, providing sensitivity, specificity, predictive values and accuracy of 100%, and giving a final result for colistin resistant isolates after 2 – 3 hours.
PAP revealed colistin heteroresistance in seven clinical K. pneumoniae isolates, initially identified as colistin-susceptible based on MIC value of BMD (≤ 2 μg/mL). The mean rate of resistant subpopulations was 7.6 x 10-7 % (0.0000076) and they showed MICs ranging from 4 to 32 μg/mL. Interestingly, all heteroresistant K pneumoniae were resistant or intermediately susceptible to colistin by disc diffusion test except one isolate, where the highest colistin concentration of growth of its resistant subpopulation in PAP was very low (3 μg/mL