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Synopses of Research Articles How Group A Streptococci Hide in Macrophages DOI: 10.1371/journal.pmed.0030095 In the past 10 years, evidence has as reservoirs for intracellular bacteria suggested that group A streptococci (GAS) during the acute tissue infection. adhere to epithelial cells and invade them. The data suggest that this could In 1994, LaPenta and colleagues found be a mechanism to avoid antibiotic that GAS could invade human epithelial eradication, which might explain why cells, in some cases better than classical a high bacterial load was present even intracellular bacterial pathogens such as in tissues collected after prolonged Listeria and Salmonella spp. can. intravenous antibiotic therapy. The Several studies quickly confi rmed this authors also note that the localization landmark fi nding and produced further of GAS varied and depended on the evidence to support this mechanism. severity of tissue infection; intracellular One study showed that high-frequency localization was most frequent in DOI: 10.1371/journal.pmed.0030095.g001 invasion needed expression of M protein noninfl amed tissue, which also had a (a surface protein, variation in which low bacterial load. Osterlund’s study had Human macrophages are host cells for provides the basis of Lancefi eld’s method already shown that intracellular GAS intracellular group A streptococci. The of serotyping GAS) and/or fi bronectin- was present in pharyngeal epithelial and fi gure shows viable (green) bacteria within binding proteins such as SfbI. Another macrophage-like cells of patients with a macrophage (cell nuclei in red). study found that the