Prevalence and resistance mechanisms of common bacterial respiratory pathogens.

Organisms causing common infections of the respiratory tract are becoming increasingly resistant to antimicrobial agents. In 1990-1991 between 15% and 20% of isolates of Streptococcus pneumoniae from the United States had MICs of penicillin G of > or = 0.1 microgram/mL and 2%-3% had MICs of > or = 1.0 microgram/mL. The percentage of isolates that are resistant is even higher in other parts of the world. Although most penicillin-resistant strains of S. pneumoniae are susceptible to broad-spectrum cephalosporins, a few isolates resistant to cefuroxime, cefotaxime, and ceftriaxone have appeared. Unlike other respiratory pathogens in which the production of beta-lactamase is responsible for resistance, S. pneumoniae exhibits resistance that is caused by alterations in penicillin-binding proteins. Consequently, beta-lactam/beta-lactamase inhibitor combinations have no particular value against resistant pneumococci. Furthermore, penicillin-resistant pneumococci are often coresistant to macrolides, sulfa-based drugs, and tetracycline. Knowledge of how resistance is attained presumably will further the development of new strategies for treatment. The mechanisms of resistance of pneumococci and other common respiratory pathogens (particularly Haemophilus influenzae and Moraxella catarrhalis) to standard antimicrobial agents are examined in this report.