ANTIBIOTIC-RESISTANCE DUE TO REDUCED PERM EABILITY IN GRAM-NEGATIVE BACTERIA

Due to their outer membrane, Gram negative bacteria are the only germs which can resist antibiotics by a mechanism of reduced permeability. This outer hydrophobic membrane allows hydrophilic molecules to pass o nly through its aqueous pores. The transmembrane pores have a trimere structure with a monomere component acting as an aqueous channel. Mean pore diameter is 1 to 1.2 nm. Changes in the absolute number of pores or in qualitative function reduce the diffusion of antibiotics enteri ng the cell. This mechanism of reduced permeability can lead to cross resistance to several families of antibiotics. It is difficult to dete rmine the clinical incidence since such resistances are not always det ected. The species most often involved are enterobacteria including Kl ebsiella, Enterobacter, Serratia and Salmonella. For Pseudomonas aerug inosa, resistance to imipenem by reduced permeability results from a d eficit in protein D2 and concerns 12 to 15% of the strains identified in French Hospitals. Reduced permeability is particularly effective wh en associated with another mechanism of resistance allowing the bacter ia to express a higher level of resistance.