Anti-invasive activity of bovine lactoferrin towards group A streptococci

Group A streptococci (GAS) are able to invade cultured epithelial and endothelial cells without evidence of intracellular replication. GAS, like other facultative intracellular bacterial pathogens, evolved such ability to enter and to survive within host cells avoiding the host defences, and bacterial intracellular survival could explain the recurrence of infections. We report here that 1 mg bovine lactoferrin (bLf)/mL significantly hindered the in vitro invasion of cultured epithelial cells by GAS isolated from patients suffering from pharyngitis and completely inhibited the invasiveness of GAS pretreated with subinhibiting concentrations of erythromycin or ampicillin. One milligram of bLf per millilitre was also able to increase the number of epithelial cells undergoing apoptosis following GAS invasion, although the number of intracellular GAS in the presence of bLf decreased by about 10-fold. The ability of bLf to decrease GAS invasion was confirmed by an in vivo trial carried out on 12 children suffering from pharyngitis and already scheduled for tonsillectomy. In tonsil specimens from children treated for 15 days before tonsillectomy with both oral erythromycin (500 mg t.i.d. (three times daily)) and bLf gargles (100 mg t.i.d.), a lower number of intracellular GAS was found in comparison with that retrieved in tonsil specimens from children treated with erythromycin alone (500 mg t.i.d.).