Porins are proteins that are located in the outer membrane of gram negative bacteria. The porin functions as a channel from outside of the cell to the periplasm. Periplasm is the region between the outer and inner membranes of the bacteria. Porin channels vary in the size of the pore in the cell. Bacteria typically have a variety of porins that are important for the transport of nutrients needed by the cell. Passage of antibiotics into gram negative cells occurs through the porin channels. Many bacteria have developed resistance to antibiotics by altering the porin channel so that the antibiotic can no longer pass into the cell. For example the porin OprD is utilized for the transport of imipenem into the bacteria. In some strains of Pseudomonas aeruginosa they have altered the structure of the OprD porin channel and as a result become resistant the antibiotic imipenem. Some other strains that have developed resistance include: Enterobacter aerogenes and Klebsiella spp. against imipenem, Vancomycin intermediate-resistant S. aureus or VISA strains with thickened cell wall trapping vancomycin, Many Gram-negative bacteria against aminoglycosides, and Many Gram-negative bacteria against quinolones.
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