Antibiotic Resistance in H. influenzae

• Until the early 1970s all strains of H. influenzae were susceptible to antibiotics.

• In 1973 the first isolate resistant to ampicillin and producing β-lactamase was reported. This was rapidly followed by strains resistant to tetracycline, chloramphenicol and trimethoprim or multiresistant to the same antibiotics emerged in all parts of the world.
• Prevalence of resistance has remained reasonably constant over the past 10 years and in Europe and ranges from 10 to 20% in most countries.
• Large integrative and conjugative resistance elements encode most of the ampicillin (TEM β-lactamase producing), tetracycline and chloramphenicol resistance.
• Ampicillin resistance also arises from ROB-β-lactamase probably associated with small plasmids. Increasingly, strains are being isolated, which are β-lactamase negative (1% BLNAR), and the mechanism of resistance in these strains has been shown to be associated with mutations in penicillin-binding protein genes.
• 1% chloramphenicol resistant (Chloramphenicol acetyl transferase: CAT).Trimethoprim resistance arises from mutations in chromosomal dihydrofolate reductase.

AMH.