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Ampicillin resistance in Haemophilus influenzae: identification of resistance mechanisms
A J Reid1, I N Simpson, P B Harper
1Bacteriology Department, Medical School, University of Edinburgh, U.K.
Abstract:
The incidence and mechanisms of ampicillin resistance (MIC greater than 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 beta-lactamase-inhibition studies demonstrated that production of the TEM-1 beta-lactamase was the principal mechanism of resistance in nine (60%) strains. Radiolabelling revealed that one beta-lactamase-positive strain also had an unusual penicillin-binding protein (PBP) profit. No beta-lactamase activity was detected in the other six (40%) ampicillin-resistant strains. Two beta-lactamase-negative ampicillin-resistant strains had atypical PBP profiles. SDS-PAGE analysis showed that four beta-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.
Insights
Ampicillin resistance in Haemophilus influenzae is driven by multiple mechanisms. TEM-1 beta-lactamase is common, but altered outer membrane proteins and penicillin-binding proteins also contribute to resistance in clinical isolates.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Ampicillin resistance poses a significant challenge in treating Haemophilus influenzae infections.
- Understanding resistance mechanisms is crucial for effective antimicrobial therapy.
Purpose of the Study:
- To investigate the incidence and mechanisms of ampicillin resistance in clinical isolates of Haemophilus influenzae.
- To identify the specific molecular factors contributing to ampicillin resistance.
Main Methods:
- Analysis of 105 clinical isolates of Haemophilus influenzae.
- Isoelectric focusing and beta-lactamase inhibition assays.
- Radiolabelling and SDS-PAGE for protein analysis.
Main Results:
- 14.3% of isolates showed ampicillin resistance.
- TEM-1 beta-lactamase production was identified in 60% of resistant strains.
- Other mechanisms included altered penicillin-binding proteins and outer membrane protein profiles.
Conclusions:
- Multiple mechanisms contribute to ampicillin resistance in Haemophilus influenzae.
- These mechanisms can act individually or in combination.
- Resistance is linked to non-serotypable strains and specific biotypes.