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Characterization of an ampicillin-resistant Haemophilus influenzae type B
Abstract:
A 28-year-old female in Denver was found in early 1974 to have frontal sinusitis, osteomyelitis, and bacteremia due to Haemophilus influenzae, type B. The minimal inhibitory concentration of ampicillin for this organism was 100 mug/ml and the minimal bactericidal concentration was >100 mug/ml. It was inhibited by chloramphenicol at 0.4 mug/ml. Further studies demonstrated that ampicillin and methicillin were synergistic against this organism. It was shown to produce a diffusible beta-lactamase. Transferase of resistance from this organism to a susceptible Haemophilus parainfluenzae and a reciprocal transfer were accomplished. A test for transformation was negative as was a test for reversal of resistance by ethylenediaminetetraacetic acid.
Insights
A severe Haemophilus influenzae type B infection was treated with antibiotics. The bacteria showed resistance to ampicillin but were susceptible to chloramphenicol, with synergistic effects noted between ampicillin and methicillin.
Area of Science:
- Medical Microbiology
- Infectious Diseases
- Clinical Bacteriology
Background:
- Haemophilus influenzae type B (Hib) infections can cause severe invasive diseases.
- Antibiotic resistance in bacterial pathogens is a growing public health concern.
Observation:
- A patient presented with frontal sinusitis, osteomyelitis, and bacteremia caused by Hib.
- The isolated Hib strain exhibited high-level resistance to ampicillin (MIC 100 µg/ml, MBC >100 µg/ml).
- Chloramphenicol demonstrated potent activity against the strain (MIC 0.4 µg/ml).
Findings:
- The Hib strain produced a diffusible beta-lactamase, explaining its ampicillin resistance.
- Ampicillin and methicillin showed synergistic activity against this resistant strain.
- Genetic transfer of ampicillin resistance was demonstrated between Hib and Haemophilus parainfluenzae.
Implications:
- This case highlights the emergence of ampicillin-resistant Hib strains and the importance of susceptibility testing.
- Understanding beta-lactamase production and resistance transfer mechanisms is crucial for guiding antimicrobial therapy.
- The synergistic activity of ampicillin and methicillin warrants further investigation for potential therapeutic applications.