Emergence of colistin-resistant Klebsiella pneumoniae in Poland.

In recent years, colistin has been the drug of choice for treatment of nosocomial infections, especially in bloodstream infections, lower respiratory tract infections, or urinary tract infections. In this study, 65 multidrug-resistant Klebsiella pneumoniae isolated from different clinical samples were included. Minimum inhibitory concentration (MIC) of colistin was detected by broth microdilution method in three different ways. For selected K. pneumoniae strains, eazyplex SuperBug mcr-1 test was performed. This test detects mcr-1 gene, which encodes a colistin-resistance determinant. Most of the analyzed K. pneumoniae strains were resistant to colistin in all applied methods. The exception was two strains, where MIC of colistin was 2 mg/L in SensiTest Colistin and MIC-Strip Colistin tests. In MIC COL test, MIC for these strains was 4 mg/L. All analyzed strains produced extended-spectrum beta-lactamases and 11 (16.9%) metallo-beta-lactamases. Eleven (16.9%) K. pneumoniae strains were resistant to all antibiotics, whereas 17 (26.1%) were susceptible to only one drug. Colistin MIC values varied from 2 to >64 mg/L in MIC-Strip Colistin test; from 2 to >16 mg/L in SensiTest Colistin and from 4 to >16 mg/L in MIC COL test. None of the analyzed K. pneumoniae strains carried mcr-1 gene. Data of this work suggest that resistance to colistin emerged among multidrug-resistant K. pneumoniae strains. The tests allowed for reliable estimation of susceptibility to colistin and could be used in microbiological diagnostics.