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Mechanisms of ampicillin resistance in Haemophilus influenzae from respiratory tract
Abstract:
13 of 100 consecutive isolates of Haemophilus influenza obtained from respiratory specimens over the six months to June, 1979, had diminished sensitivity to ampicillin. 6 of the 13 strains produced beta-lactamase, whilst the remaining 7 had no evidence of this enzyme, either in whole cells or in extracts prepared by sonication. The minimum inhibitory concentration of ampicillin for the penicillinase-negative strains ranged from 1 mg/l to 8 mg/l on repeated testing with a carefully controlled agar-dilution technique. The findings contrast strongly with those of earlier surveys of the sensitivity of respiratory strains of H. influenzae to ampicillin and confirm the existence of two mechanisms of resistance to ampicillin in the species.
Insights
Ampicillin resistance in Haemophilus influenzae is increasing. Two distinct resistance mechanisms were identified in respiratory isolates: beta-lactamase production and other uncharacterized methods.
Area of Science:
- Microbiology
- Antimicrobial Resistance
Background:
- Haemophilus influenzae is a significant respiratory pathogen.
- Ampicillin was previously a reliable treatment option.
Purpose of the Study:
- To investigate ampicillin sensitivity in recent respiratory isolates of Haemophilus influenzae.
- To identify mechanisms of ampicillin resistance.
Main Methods:
- Agar-dilution technique for determining minimum inhibitory concentrations.
- Testing for beta-lactamase production in bacterial isolates.
Main Results:
- 13% of isolates showed reduced ampicillin sensitivity.
- Beta-lactamase was detected in 6 isolates; 7 isolates showed resistance without beta-lactamase.
- Penicillinase-negative strains had minimum inhibitory concentrations of 1-8 mg/l.
Conclusions:
- Two distinct mechanisms of ampicillin resistance exist in Haemophilus influenzae.
- Emerging resistance necessitates ongoing surveillance of antimicrobial susceptibility.