Microbiology of common infections in the upper respiratory tract

The management of upper respiratory tract infections has become more difficult because of the recent increase in the number of penicillin-resistant organisms. The bacteria that predominate in otitis media and sinusitis can resist penicillin through the production of the enzyme beta-lactamase (Haemophilus influenzae and Moraxella catarrhalis in acute infections and Staphylococcus aureus and Prevotella and Fusobacteria spp in chronic infections) or through changes in penicillin-binding sites (Streptococcus pneumoniae). beta-lactamase-producing bacteria can express their pathogenicity directly through their ability to cause infections and indirectly by production of the enzyme, thus protecting penicillin-susceptible pathogens from penicillins. This phenomenon may explain penicillin's failure in the treatment of Group A beta-hemolytic streptococcal (GABHS) tonsillitis. An additional cause for penicillin failure is the absence among the normal tonsillar bacterial flora of streptococcal species that are capable of interfering with the growth of GABHS. Proper use of antimicrobial therapy, including those therapies that are effective against penicillin-resistant bacteria, is the cornerstone of management of upper respiratory tract infections.