title: Ampicillin resistance in Hemophilus parainfluenzae.
abstract: Ampicillin resistance among strains of Hemophilus is usually due to production of beta-lactamase. This paper reports the isolation of a strain of H. parainfluenzae resistant to ampicillin with no detectable beta-lactamase or amidase activity. The organism, isolated from the blood of a patient who had aortic valve endocarditis, gave a zone diameter consistent with ampicillin sensitivity when tested by disc diffusion in Mueller-Hinton agar supplemented with 1% IsoVitaleX and 1% hemoglobin. Broth dilution testing in Levinthal medium, however, revealed the following minimal inhibitory cencentrations: ampicillin, 32 micrograms/ml; penicillin, 256 micrograms/ml; methicillin, 128 micrograms/ml; carbenicillin, 128 micrograms/ml; and cephalothin and chloramphenicol, 1.0 micrograms/ml. The results of acidimetric, iodometric, and chromogenic cephalosporin methods for detection of beta-lactamase were negative. Beta-lactamase activity could not be demonstrated in cell sonicates or induced by growth of the cells in antibiotic-containing medium. In addition, no extracellular degradation of either ampicillin or penicillin could be demonstrated.
mesh_terms: D000328:Adult; D000667:Ampicillin / Q000494:pharmacology* / Q000627:therapeutic use; D004697:Endocarditis, Bacterial / Q000188:drug therapy / Q000382:microbiology; D006190:Haemophilus / Q000187:drug effects* / Q000201:enzymology; D006192:Haemophilus Infections / Q000188:drug therapy / Q000382:microbiology; D006801:Humans; D008297:Male; D008826:Microbial Sensitivity Tests / Q000379:methods; D010403:Penicillin Resistance; D001618:beta-Lactamases / Q000378:metabolism
chemical_list: D000667:Ampicillin; D001618:beta-Lactamases