Antibiotic resistance in Haemophilus influenzae: epidemiology, mechanisms, and therapeutic possibilities.

The prevalence of antibiotic resistance in Haemophilus influenzae is increasing. The encapsulated strains of group b are the strains that are most important in the pathogenesis of severe systemic infections, and it is in this group that the incidence of resistance is highest. Strains simultaneously resistant to ampicillin, chloramphenicol, and tetracycline are rare but have been isolated in several parts of the world. Transferable antibiotic resistance is well documented, and both small (3.6 megadaltons) and large (38-42 megadaltons) plasmids mediating beta-lactamase and chloramphenicol acetyltransferase production and tetracycline resistance have been detected in H. influenzae. The possibilities for treatment of infections due to such organisms include the use of the newer cephalosporins, of a combination of a beta-lactamase inhibitor and ampicillin, and of alternate agents such as minocycline and trimethoprim. Sporadic strains resistant to these agents have also been reported.