@article{mbs:/content/journal/micro/10.1099/00221287-133-12-3383, author = "Aggeler, Robert and Then, Rudolf L. and Ghosh, Robin", title = "Reduced Expression of Outer-membrane Proteins in β-Lactam-resistant Mutants of Enterobacter cloacae", journal= "Microbiology", year = "1987", volume = "133", number = "12", pages = "3383-3392", doi = "https://doi.org/10.1099/00221287-133-12-3383", url = "https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-133-12-3383", publisher = "Microbiology Society", issn = "1465-2080", type = "Journal Article", abstract = "SUMMARY: 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 β-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-(trifluoromethyl)-3-(m-[125I]iodo-phenyl)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 β-lactam antibiotics, the basis of hyper-sensitivity of AZT-R to hydrophobic antibiotics remains to be more clearly defined.", }