A simple phenotypic method for screening of MCR-1-mediated colistin resistance.

OBJECTIVES: To evaluate a novel method, the colistin-MAC test, for phenotypic screening of acquired colistin resistance mediated by transferable mcr-1 resistance determinants, based on colistin MIC reduction in the presence of dipicolinic acid (DPA). METHODS: The colistin-MAC test consists in a broth microdilution method, in which colistin MIC is tested in the absence or presence of DPA (900 µg/mL). Overall, 74 colistin-resistant strains of Enterobacteriaceae (65 Escherichia coli and nine other species), including 61 strains carrying mcr-1-like genes and 13 strains negative for mcr genes, were evaluated with the colistin-MAC test. The presence of mcr-1-like and mcr-2-like genes was assessed by real-time PCR and end-point PCR. For 20 strains, whole-genome sequencing data were also available. RESULTS: A ≥8-fold reduction of colistin MIC in the presence of DPA was observed with 59 mcr-1-positive strains, including 53 E. coli of clinical origin, three E. coli transconjugants carrying MCR-1-encoding plasmids, one Enterobacter cloacae complex and two Citrobacter spp. Colistin MICs were unchanged, increased or at most reduced by twofold with the 13 mcr-negative colistin-resistant strains (nine E. coli and four Klebsiella pneumoniae), but also with two mcr-1-like-positive K. pneumoniae strains. CONCLUSIONS: The colistin-MAC test could be a simple phenotypic test for presumptive identification of mcr-1-positive strains among isolates of colistin-resistant E. coli, based on a ≥8-fold reduction of colistin MIC in the presence of DPA. Evaluation of the test with a larger number of strains, species and mcr-type resistance determinants would be of interest.

Values of SP-A protein in the nasal mucosa.

The paranasal sinus epithelium is exposed to the environment and therefore to a variety of biological, chemical and mechanical insults. Surfactant protein A (SP-A) is a 34-36 kD pulmonary surfactant-associated protein that appears to play an important role in mammalian first-line host defence. Recent studies have reported the possibility of local production of SP-A in the extrapulmonary organs and tissues of the human body. However, the presence of SP-A in the human paranasal sinus mucosa is not well known. The purpose of this study was to investigate the expression of SP-A protein in human turbinate mucosa and to compare the expression of SP-A mRNA in normal turbinate mucosa and turbinate mucosa of chronic rhinosinusitis patients. Reverse transcriptase polymerase chain reaction was used to detect SP-A mRNA. Student's t test was used for statistical comparison of the SP-A/GAPDH-mRNA ratio (GAPDH: glycerinaldehyde-3-phosphate dehydrogenase) of cases and controls. We found expression of SP-A mRNA in mucosa lining the inferior turbinates of healthy patients and its up-regulation in mucosa lining the inferior turbinates of patients with chronic rhinosinusitis. These results may provide targets for new therapies for chronic rhinosinusitis.