A method for discriminating carbapenem-resistant bacteria according to whether or not they develop resistance by membrane impermeability, the method including the following steps: providing a bacterial strain that is resistant to at least one carbapenem, evaluating the sensitivity of the bacterial strain with regard to at least one indicator carbapenem, on the one hand in the absence of polymyxin B nonapeptide (PMBN) and, on the other hand, in the presence of PMBN in a non-inhibitory concentration, establishing a prognosis of resistance by membrane impermeability in the case where the presence of PMBN makes it possible to significantly increase the sensitivity of the bacterial strain with regard to at least one indicator carbapenem used.
