Ampicillin resistance in Hemophilus parainfluenzae

C. N. Walker, P. W. Smith

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


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 concentrations: ampicillin, 32 μg/ml; penicillin, 256 μg/ml; methicillin, 128 μg/ml; carbenicillin, 128 μg/ml; and cephalothin and chloramphenicol, 1.0 μg/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.

Original languageEnglish (US)
Pages (from-to)229-232
Number of pages4
JournalAmerican journal of clinical pathology
Issue number2
StatePublished - 1980

ASJC Scopus subject areas

  • Pathology and Forensic Medicine


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