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J Antimicrob Chemother. 1997 Sep;40(3):365-70.

Permeability to carbapenems of Proteus mirabilis mutants selected for resistance to imipenem or other beta-lactams.

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Department of Medical Microbiology, St Bartholomew's and the Royal London School of Medicine and Dentistry, UK.


An imipenem-resistant mutant of Proteus mirabilis lacked a 26 kDa outer membrane protein (OMP). It has previously been postulated that this protein is a porin, but the present mutant, which was cross-resistant to mecillinam but not to other beta-lactams, proved as permeable to carbapenems as its parent. A mecillinam-selected mutant had similar cross-resistance yet retained the 26 kDa OMP, confirming that this protein was not important to resistance. In contrast, cefoxitin-selected mutants retained the 26 kDa protein but had diminished expression of major 41 and 44 kDa OMPs and showed reduced uptake of carbapenems, although this promoted resistance only when a carbapenemase was also present. We conclude that the imipenem-selected mutant owed its resistance to some factor other than porin loss, probably to a lesion in penicillin-binding protein 2.

[Indexed for MEDLINE]

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