Antibiotic consumption and link to resistance.

Antibiotic use in the treatment of respiratory tract infections is common in primary care. The European Surveillance of Antimicrobial Consumption (ESAC programme), collecting data from 35 countries, showed that antibiotic use was highest in southern European countries. Increased antibiotic consumption has been shown by numerous ecological studies to contribute to the emergence of antibiotic resistance in streptococci. A study comparing outpatient antibiotic consumption in the USA showed it to be similar to that in southern European countries, but macrolides, particularly azithromycin, are among the first-line agents prescribed in the USA for respiratory infections. In Europe, patients are more likely to receive a beta-lactam; and when a macrolide is indicated, clarithromycin is more likely to be prescribed than azithromycin. Streptococci resistance to macrolides can be acquired via two mechanisms: by the mef gene, which encodes for the efflux pump mechanism, producing low to moderate resistance, or the erm gene (post-transcriptional modification of the bacterial ribosomal unit), resulting in high resistance. Macrolide resistance is mediated by erm(B) and mef(A) alone or in combination. A surveillance study showed that mef was responsible for most of the macrolide resistance seen in the USA; a decrease in the number of isolates carrying mef(A) was associated with a doubling of the number of isolates carrying both mef(A) and erm(B). Higher consumption of clarithromycin in Europe correlated with a predominance of erm(B)-carrying Streptococcus pneumoniae. The erm(B) gene caused resistance in 84% of the isolates in Europe.