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Activity of cephalosporin antibiotics against Haemophilus influenzae
Abstract:
Minimum inhibitory concentrations (MICs) of nine cephalosporins were determined for 90 isolates of Haemophilus influenzae including 70 amoxycillin-resistant strains. Cefotaxime was the most active of the parenteral antibiotics tested, with a modal MIC of 0.03 mg/l, compared with ceftazidime 0.12 mg/l, cefamandole 0.25 mg/l, cefuroxime 0.5 mg/l and cefathiamidine 4 mg/l. Cefaclor was the most active of the oral cephalosporins tested, with a modal MIC of 2 mg/l compared with cephalexin 8 mg/l and cephradine 32 mg/l. Amoxycillin-sensitive and beta-lactamase-producing haemophili had similar MICs for all cephalosporins. Twenty amoxycillin-resistant beta-lactamase non-producing strains showed high MICs for all beta-lactams tested. A cell permeability barrier is postulated as a mechanism of resistance in these strains.
Insights
Cefotaxime demonstrated the highest activity against Haemophilus influenzae, including amoxycillin-resistant strains. A cell permeability barrier is suggested as a resistance mechanism in some strains.
Area of Science:
- Microbiology
- Infectious Diseases
- Pharmacology
Background:
- Haemophilus influenzae is a significant human pathogen.
- Antibiotic resistance in H. influenzae, particularly to amoxycillin, is a growing concern.
- Cephalosporins are a class of beta-lactam antibiotics used to treat bacterial infections.
Purpose of the Study:
- To evaluate the in vitro activity of nine cephalosporins against clinical isolates of Haemophilus influenzae.
- To compare the efficacy of parenteral and oral cephalosporins against amoxycillin-resistant strains.
- To investigate potential mechanisms of resistance in beta-lactamase non-producing, amoxycillin-resistant H. influenzae.
Main Methods:
- Minimum inhibitory concentrations (MICs) were determined for 90 H. influenzae isolates.
- Isolates included 70 amoxycillin-resistant strains.
- Antibiotic susceptibility testing was performed for nine cephalosporins and amoxycillin.
Main Results:
- Cefotaxime exhibited the lowest modal MIC (0.03 mg/l) among parenteral cephalosporins tested.
- Cefaclor showed the greatest activity among oral cephalosporins (modal MIC 2 mg/l).
- Amoxycillin-resistant, beta-lactamase non-producing strains displayed high MICs for all tested beta-lactams, suggesting a permeability barrier.
Conclusions:
- Cefotaxime is a highly active cephalosporin against H. influenzae, including resistant strains.
- Cephalosporin efficacy varies significantly between oral and parenteral formulations.
- Reduced cell permeability may be a key mechanism conferring resistance to beta-lactams in H. influenzae.