title: Effect of beta-lactamase location in Escherichia coli on penicillin synergy.
abstract: Resistance to ampicillin in Escherichia coli is due generally to the presence of a beta-lactamase (penicillinase). Resistant strains have been found to fall into two groups: those with high-level resistance (1,000 mug/ml or greater) and those with low-level resistance (8 to 250 mug/ml). Most of the high-level resistant organisms posses beta-lactamases whose synthesis is episomally mediated. These strains release penicillinase from the cell when they are subjected to osmotic shock. Low-level resistant strains do not release the enzyme with osmotic shock. High-level resistant strains are not susceptible to the synergistic action of a penicillinase-resistant penicillin with ampicillin. Seventy eight per cent of low-level resistant strains are susceptible to the synergistic action of ampicillin and oxacillin. The two types of beta-lactamases are similar in regard to most properties; both enzymes are subject to competitive inhibition by penicillinase-resistant penicillins. The difference in location in the cell might explain why only some strains of E. coli are susceptible to the synergistic action of penicillin combinations.
mesh_terms: D000667:Ampicillin / Q000494:pharmacology*; D004357:Drug Synergism; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology*; D005111:Extrachromosomal Inheritance; D005827:Genetics, Microbial; D009995:Osmosis; D010068:Oxacillin / Q000494:pharmacology*; D010403:Penicillin Resistance; D010405:Penicillinase / Q000378:metabolism; D065093:beta-Lactamase Inhibitors
chemical_list: D065093:beta-Lactamase Inhibitors; D000667:Ampicillin; D010405:Penicillinase; D010068:Oxacillin