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Antimicrob Agents Chemother. 1972 February; 1(2): 107-111
Copyright © 1972 American Society for Microbiology. All Rights Reserved.

Relation of ß-Lactamase Activity and Cellular Location to Resistance of Enterobacter to Penicillins and Cephalosporins

^a College of Physicians and Surgeons, Columbia University, New York, New York 10032

ABSTRACT

The Enterobacter species E. aerogenes, E. cloacae, and E. hafnia were examined for resistance to penicillin and cephalosporin derivatives. All were resistant to benzyl penicillin, ampicillin, 6 [D(–)-amino-p-hydroxyphenylacetamido] penicillanic acid, cephaloridine, cephalothin, and cephalexin. A significant number were sensitive to carbenicillin and 6 [D(–)-carboxy-3-thienylacetamido] penicillanic acid. No differences among the three species were noted. The ß-lactamase activity was cell-bound, and was not released by osmotic shock, toluene treatment, or diphenylamine treatment. It was rarely released into the growth medium. The ß-lactamase activity was primarily directed against cephalosporin derivatives. Synthesis of ß-lactamase was chromosomally mediated. Resistance to ampicillin seemed to be partly related to entry of the molecule into the bacteria since exposure to ethylenediaminetetraacetate lowered the minimal inhibitory concentration.

¹ Career Scientist, New York City Health Research Council.