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[Ampicillin-resistant Haemophilus influenzae. Prevalence in isolates from Danish children]
T Ejlertsen1, R B Dessau, T Højbjerg
1Klinisk mikrobiologisk afdeling, Aalborg Sygehus.
Insights
Ampicillin resistance in Haemophilus influenzae (H. influenzae) increased, particularly in Copenhagen, due to beta-lactamase production. This highlights the growing challenge of treating H. influenzae infections with ampicillin.
Area of Science:
- Clinical Microbiology
- Infectious Diseases
- Bacterial Resistance
Background:
- Haemophilus influenzae (H. influenzae) is a significant pathogen causing various childhood infections.
- Ampicillin was a common treatment, but resistance has emerged.
- Beta-lactamase production is a primary mechanism of ampicillin resistance in H. influenzae.
Purpose of the Study:
- To assess the prevalence of ampicillin resistance in H. influenzae strains from pediatric patients in Denmark.
- To track the temporal trends of beta-lactamase production in H. influenzae.
- To correlate beta-lactamase production with ampicillin resistance.
Main Methods:
- Collected 2766 H. influenzae strains from various clinical specimens (respiratory, CSF, blood) from children (0-15 years).
- Tested ampicillin susceptibility using disc/tablet diffusion.
- Assessed beta-lactamase production using a chromogenic cephalosporinase test.
Main Results:
- In Northern Jutland, beta-lactamase production in non-encapsulated H. influenzae rose from 2.5% (1986) to 9.3% (1993).
- In Copenhagen, beta-lactamase production in non-encapsulated H. influenzae increased from 6.3% (1986) to 20.7% (1993).
- H. influenzae type b showed beta-lactamase production rates of 4.1% (Northern Jutland) and 8.5% (Copenhagen). No ampicillin resistance was observed without beta-lactamase production.
Conclusions:
- Ampicillin resistance in H. influenzae is primarily mediated by beta-lactamase production.
- A significant increase in beta-lactamase-producing H. influenzae was observed, especially in Copenhagen.
- The findings underscore the declining efficacy of ampicillin for H. influenzae infections and the need for alternative treatments.
Abstract:
The prevalence of ampicillin-resistance was assessed among a total of 2766 strains of H. influenzae isolated from lower respiratory tract secretions, middle ear secretions, spinal fluid specimens, and blood cultures from children 0-15 years of age tested in two separate counties in Denmark during the period from 1986 to May, 1993. All strains were tested for susceptibility to ampicillin with disc or tablet diffusion technique and strains were examined for beta-lactamase production with a chromogenic cephalosporinase test. In the county of Northern Jutland the rate of beta-lactamase production in non-encapsulated H. influenzae was 2.5% in 1986 rising to 9.3% in 1993. The rate of beta-lactamase production in H. influenzae type b was 4.1% without any rise. In the county of Copenhagen the rate of beta-lactamase production in non-encapsulated H. influenzae rose from 6.3% in 1986 to 10.6% in 1992. In 1993 a further increase to 20.7% was noticed. This year the number of specimens sent to the laboratory and the number of H. influenzae isolated were lower compared to previous years. Thus a different selection of patients may explain the increase in the rate of beta-lactamase production in 1993. The rate of beta-lactamase production in H. influenzae type b was 8.5%. No strains were resistant to ampicillin in diffusion test other than the beta-lactamase producers.