Endemic and epidemic Streptococcus pyogenes strains : reservoirs in recurrent pharyngotonsillitis reservoirs in recurrent pharyngotonsillitis reservoirs in recurrent pharyngotonsillitis

Abstract: The bacterium Streptococcus pyogenes is a common human pathogen known to cause bothuncomplicated and severe infections. Epidemics of invasive disease caused by S. pyogenesserotype T1 were seen in the county of Uppsala, Sweden, in 19881989 and 1994. Usingrandom amplified polymorphic DNA analysis (RAPD) it was possible to distinguish betweenthe two epidemics. These two epidemics appeared to have been caused by different clones of S. pyogenes.Recurrence of streptococcal pharyngotonsillitis after seemingly adequate penicillintreatment is common. By using RAPD, identical DNA-fingerprinting patterns were found in pre- and post-treatment isolates of S. pyogenes. The possibility that recurrences could becaused by an intracellular reservoir of S. pyogenes protected from eradication by extracellularlyactive antibiotics such as penicillin was investigated.S. pyogenes was capable of penetrating cultured respiratory epithelial cells and ofintracellular survival for up to seven days. A method for culture tonsillar biopsies wasdeveloped in order to mimic the in vivo situation. The. biopsies were found to survive for atleast 48 hours in such cultures. Biopsies infected with S. pyogenes were rapidly damaged.Immunoperoxidase staining of sections from infected biopsies showed a few scattered epithelial cells harbouring intracellular S. pyogenes.Respiratory epitbelial cells from patients with recurrent pharyngotonsillitis and tonsilsfrom asymptomatic S. pyogenes carriers were investigated for the presence of intracellular S. pyogenes. Using immunohistochemistry and transmission electron microscope, S. pyogenes was found in pharyngeal epithelial cells in 13 out of 14 patients with recurrent pharyngotonsillitis (93%) and in macrophage-like cells of the tonsillar core in 8 out of 11 asymptomaticS. pyogenes carriers (73%). The results from these two in vivo studies strongly support thehypothesis that intracellular S. pyogenes, in macrophage-like cells or in epithelial cells, mayconstitute a reservoir with the potential to cause reinfection.It is proposed that the epidemiology of S. pyogenes can be explained by cocitculation ofepidemic and endemic strains. The endemic strains may be more likely to persist intracellularlyin their hosts than the epidemic strains.