Ampicillin resistance in Haemophilus influenzae: identification of resistance mechanisms
Open Access
- 1 November 1987
- journal article
- research article
- Published by Oxford University Press (OUP) in Journal of Antimicrobial Chemotherapy
- Vol. 20 (5), 645-656
- https://doi.org/10.1093/jac/20.5.645
Abstract
The incidence and mechanisms of ampicillin resistance (MIC > 1 mg/l) were investigated in 105 clinical isolates of Haemophilus influenzae collected in Edinburgh during 1983/4. Fifteen (14.3%) ampicillin-resistant strains were identified and these were non-serotypable and comprised six biotypes. Isoelectric focusing and β-lactamase-inhibition studies demonstrated that production of the TEM-1 β-lactamase was the principal mechanism of resistance in nine (60%) strains. Radiolabelling revealed that one β-lactamase-positive strain also had an unusual penicillin-binding protein (PBP) profit. No β-lactamase activity was detected in the other six (40%) ampicillin-resistant strains. Two β-lactamase-negative ampicillin-resistant strains had atypical PBP profiles. SDS-PAGE analysis showed that four β-lactamase-negative ampicillin-resistant strains, including one with altered PBPs, exhibited outer membrane protein profiles which differed from those of sensitive strains of the same biotype. The ampicillin-resistance mechanism of the remaining strain could not be determined. Thus, several resistance mechanisms, either acting individually or in combination, are implicated in ampicillin resistance in H. influenzae.Keywords
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