Introduction. The worldwide emergence of carbapenem resistance in Gram-negative bacteria makes the development of simple tests mandatory to identify antimicrobial resistance mechanisms. Enzymatic and membrane barriers are the prominent resistance mechanisms described in these bacteria. Several tests are currently used to detect carbapenemase activities.Aim. However, a simple test for the identification of membrane-associated mechanisms of resistance is not yet available and this mechanism is often inferred after the exclusion of a carbapenemase in carbapenem-resistant Gram-negative bacteria.Methodology. Different media (liquid and solid) containing a membrane permeabilizer were tested to identify the existence of a membrane barrier. Here, polymyxin B nonapeptide (PMBN) was selected to bypass the role of impermeability in clinical carbapenem-resistant Enterobacteriaceae, including Escherichia coli, Enterobacter cloacae , Klebsiella pneumoniae and Klebsiella aerogenes isolates. In parallel, the expression of porins (OmpC and OmpF types) was checked in the various bacterial strains in order to search for a correlation between the restoration of susceptibility and the expression of porin.Results. Using a large number of clinical isolates, PMBN associated with a carbapenem allowed us to detect porin-deficient isolates with a sensitivity ranging from 89 to 93 % and a specificity ranging from 86 to 100 %.Conclusion. This paves the way for a diagnostic assay allowing the detection of this membrane-associated mechanism of resistance in Enterobacteriaceae.
Keywords: Gram-negative bacteria; carbapenem resistance; membrane permeabilizer; porins.