Reduced ability of penicillin to eradicate ingested group A streptococci from epithelial cells: Clinical and pathogenetic implications

Background. Group A streptococci (Streptococcus pyogenes; GAS) invades human epithelial cell lines. Failure of penicillin to eradicate GAS from the throats of patients, especially those who are GAS carriers, has been increasingly reported. However, there has been no comprehensive evaluation of how effectively antibiotics that are used to treat GAS enter upper respiratory tract epithelial cells and kill internalized GAS. We examined the viability of ingested, intracellular GAS after epithelial cell exposure to antibiotics commonly recommended for therapy of GAS infections. Methods. A human laryngeal epithelial cell line (HEp-2) was used. Three techniques were used to study antibiotic (penicillin V, erythromycin, azithromycin, cephalothin, and clindamycin) killing of ingested GAS: examination by electron microscopy of ultrathin sections of ingested GAS, qualitative determination of intra-epithelial cell antibiotic, and special stain evaluation of intracellular GAS viability after epithelial cell exposure to antibiotics. Results. GAS survived intracellularly despite exposure of the GAS-containing epithelial cells to penicillin. In contrast, there was killing of ingested GAS after exposure of epithelial cells to either erythromycin or azithromycin. Electron microscopy confirmed a lack of intracellular GAS fragmentation (cell death) after exposure of epithelial cells to penicillin in contrast to obvious GAS fragmentation after epithelial cell exposure to erythromycin or azithromycin. Cephalothin, a cephalosporin, and clindamycin were more effective in killing ingested GAS than was penicillin, but they were less effective than erythromycin or azithromycin. Conclusions. These observations strongly suggest that if the GAS upper respiratory tract carrier state results from intra-epithelial cell GAS survival, the failure of penicillin to kill ingested GAS may be related to a lack of effective penicillin entry into epithelial cells. These unique observations may have clinical implications for understanding GAS respiratory tract carriers and managing GAS infections.