title: Multidrug resistance of a porin deletion mutant of Mycobacterium smegmatis.
abstract: Mycobacteria contain an outer membrane of unusually low permeability which contributes to their intrinsic resistance to many agents. It is assumed that small and hydrophilic antibiotics cross the outer membrane via porins, whereas hydrophobic antibiotics may diffuse through the membrane directly. A mutant of Mycobacterium smegmatis lacking the major porin MspA was used to examine the role of the porin pathway in antibiotic sensitivity. Deletion of the mspA gene caused high-level resistance of M. smegmatis to 256 microg of ampicillin/ml by increasing the MIC 16-fold. The permeation of cephaloridine in the mspA mutant was reduced ninefold, and the resistance increased eightfold. This established a clear relationship between the activity and the outer membrane permeation of cephaloridine. Surprisingly, the MICs of the large and/or hydrophobic antibiotics vancomycin, erythromycin, and rifampin for the mspA mutant were increased 2- to 10-fold. This is in contrast to those for Escherichia coli, whose sensitivity to these agents was not affected by deletion of porin genes. Uptake of the very hydrophobic steroid chenodeoxycholate by the mspA mutant was retarded threefold, which supports the hypothesis that loss of MspA indirectly reduces the permeability by the lipid pathway. The multidrug resistance of the mspA mutant highlights the prominent role of outer membrane permeability for the sensitivity of M. smegmatis to antibiotics. An understanding of the pathways across the outer membrane is essential to the successful design of chemotherapeutic agents with activities against mycobacteria.
authors.affiliation: Department of Microbiology, University of Alabama at Birmingham, 609 Bevill Biomedical Research Building, 845 19th St. South, Birmingham, AL 35294, USA.
authors.forename: Joachim
authors.initials: J
authors.lastname: Stephan
authors.forename: Claudia
authors.initials: C
authors.lastname: Mailaender
authors.forename: Gilles
authors.initials: G
authors.lastname: Etienne
authors.forename: Mamadou
authors.initials: M
authors.lastname: Daffé
authors.forename: Michael
authors.initials: M
authors.lastname: Niederweis
mesh_terms: D000617:Aminoglycosides / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000494:pharmacology*; D000995:Antitubercular Agents / Q000494:pharmacology; D001692:Biological Transport; D002473:Cell Wall / Q000378:metabolism; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003470:Culture Media; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics; D017353:Gene Deletion; D050356:Lipid Metabolism; D008826:Microbial Sensitivity Tests; D020102:Mycobacterium smegmatis / Q000187:drug effects* / Q000235:genetics*; D018272:Porins / Q000235:genetics*; D047090:beta-Lactams / Q000494:pharmacology
chemical_list: D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D000995:Antitubercular Agents; D003470:Culture Media; D018272:Porins; D047090:beta-Lactams