title: Ampicillin resistance of Shigella sonnei.
abstract: The ampicillin resistance of clinical isolates of Shigella sonnei is due to beta-lactamase production. Two kinds of resistance are found: low level, nontransmissible; and high level, tranmissible. The nontransmissible type of resistance results from a chromosomal mutation which increases the production of a beta-lactamase that hydrolyses cephalosporins relatively rapidly and gives cephalothin resistance. The transmissible type of resistance is due to an R factor mediating the synthesis of a different beta-lactamase that does not significantly hydrolyze cephalosporins or confer cephalothin resistance. One clinical isolate is shown to possess simultaneously both these mechanisms of ampicillin resistance.
mesh_terms: D000668:Ampicillin Resistance / Q000502:physiology*; D004352:Drug Resistance, Microbial / Q000502:physiology; D004926:Escherichia coli / Q000187:drug effects; D008826:Microbial Sensitivity Tests; D010403:Penicillin Resistance / Q000502:physiology*; D012764:Shigella sonnei / Q000187:drug effects* / Q000201:enzymology; D013045:Species Specificity; D001618:beta-Lactamases / Q000096:biosynthesis
chemical_list: D001618:beta-Lactamases