Bacterial resistance in the new millennium. Its impact on antibiotic selection for respiratory tract infections.

The targets of antibiotic intervention in respiratory tract infections continue to change. For example, the minimum inhibitory concentrations (MICs) of beta-lactams for Streptococcus pneumoniae have increased up to 100-fold in recent years. Because the mechanism of resistance in this respiratory tract pathogen is an alteration in penicillin-binding proteins, the higher the MIC of penicillin, the higher the MICs of all beta-lactams. Macrolide resistance in S pneumoniae is highly prevalent in many countries and correlates with penicillin resistance. Because the mechanisms of resistance to tetracyclines, chloramphenicol, and macrolides share the same transposon, resistance to multiple antibiotics in S pneumoniae is common. Although the prevalence of resistance to fluoroquinolones in S pneumoniae is low, it may well increase once these agents are widely prescribed for pediatric patients. The prevalence of ss-lactamase-producing strains of Haemophilus influenzae is stable even though it differs among individual countries. However, beta-lactam activity against H influenzae varies considerably worldwide. The efficacy of macrolide activity against H influenzae is questionable, and resistance to the fluoroquinolones is rare. Virtually all strains of Moraxella catarrhalis produce beta-lactamase. Most oral antibiotics, including the macrolides, are more active against M catarrhalis than H influenzae. Clearly, reassessment of current prescribing practices is critical if antibiotic efficacy is to be preserved and the risk for selection of resistance minimized in the new millennium.