The effects of macrolides on the expression of bacterial virulence mechanisms

Macrolides are unique among the various classes of antimicrobial agents because of the manner in which they interact with pathogens and the host immune system to produce a clinical response. Conventional efficacy explanations require the serum or tissue concentration of the macrolide to exceed the MIC of the macrolide to account for bacteriostatic activity. However, at concentrations below the MIC, there are other effects on the expression of proteinaceous virulence factors which could prevent the pathogen from establishing or expanding an infection. The purpose of this review is to describe these effects and to provide an in-vivo scenario delineating the role of macrolides and leucocytes as they contribute to clinical efficacy.