title: Reduced expression of outer-membrane proteins in beta-lactam-resistant mutants of Enterobacter cloacae.
abstract: Two antibiotic-resistant mutants of Enterobacter cloacae (AZT-R and AMA-R), obtained by selection with aztreonam and carumonam, were studied. Both mutants were resistant to beta-lactam antibiotics. In addition, AMA-R was also resistant to chloramphenicol, trimethoprim and brodimoprim, whereas AZT-R was hypersensitive to these compounds. Cytoplasmic and outer membranes of these bacteria were separated by sucrose density gradient centrifugation. Analysis of the outer membranes using SDS-PAGE showed marked changes in the bands corresponding to the porins (between 35 and 40 kDa). In the two mutants, the 39 kDa band was reduced to approximately 30% of the wild-type and the 36.5 kDa band was absent. Labelling of the outer membranes with the hydrophobic photolabel 3-(trifluoomethyl)- 3-(m-[125I]iodophenyl)diazirine ([125I]TID) enabled the above bands as well as a 28.8 kDa band to be identified as integral membrane proteins, thus supporting the suggestion that they correspond to porins and OmpA protein, respectively. Whereas the changes observed in outer-membrane proteins are assumed to be responsible for resistance to beta-lactam antibiotics, the basis of hypersensitivity of AZT-R to hydrophobic antibiotics remains to be more clearly defined.
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism*; D004352:Drug Resistance, Microbial / Q000235:genetics; D004591:Electrophoresis, Polyacrylamide Gel; D004754:Enterobacter / Q000187:drug effects* / Q000235:genetics; D004755:Enterobacteriaceae / Q000187:drug effects*; D009154:Mutation; D010743:Phospholipids / Q000378:metabolism; D047090:beta-Lactams
chemical_list: D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D010743:Phospholipids; D047090:beta-Lactams