Mechanisms of resistance to β-lactam antibiotics in Acinetobacter calcoaceticus

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Abstract
Examination of 12 strains of Acinetobacter calcoaceticus revealed that the strains expressed different constitutive levels of β-lactamase. Mutants resistant to cefoxitin, cefoperazone or ceftazidime were selected from a strain producing a low level of β-lactamase. All the mutants showed no change in expression of β-lactamase, but produced penicillin-binding proteins with altered expression and/or affinity for β-lactamase. In addition, the outer membrane of the mutants showed decreased permeability (40–80% that of the parent strain) towards small hydrophilk solutes, together with diminished production of a 46–5 kDa porin protein. It was concluded that the enhanced resistance to β-lactamase in the A. calcoaceticus mutants was the result of interplay between the altered penicillin binding proteins and the reduced outer membrane permeability.

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