bDespite the high frequency of asymptomatic carriage of bacterial pathogens, we understand little about the bacterial molecular genetic underpinnings of this phenomenon. To obtain new information about the molecular genetic mechanisms underlying carriage of group A Streptococcus (GAS), we performed whole-genome sequencing of GAS strains recovered from a single individual during acute pharyngitis and subsequent asymptomatic carriage. We discovered that compared to the initial infection isolate, the strain recovered during asymptomatic carriage contained three single nucleotide polymorphisms, one of which was in a highly conserved region of a gene encoding a sensor kinase, liaS, resulting in an arginine-to-glycine amino acid replacement at position 135 of LiaS (LiaS R135G ). Using gene replacement, we demonstrate that introduction of the carrier allele (liaS R135G ) into a serotype-matched invasive strain increased mouse nasopharyngeal colonization and adherence to cultured human epithelial cells. The carrier mutation also resulted in a reduced ability to grow in human blood and reduced virulence in a mouse model of necrotizing fasciitis. Repair of the mutation in the GAS carrier strain restored virulence and decreased adherence to cultured human epithelial cells. We also provide evidence that the carrier mutation alters the GAS transcriptome, including altered transcription of GAS virulence genes, providing a potential mechanism for the pleiotropic phenotypic effects. Our data obtained using isogenic strains suggest that the liaS R135G mutation in the carrier strain contributes to the transition from disease to asymptomatic carriage and provides new information about this poorly described regulatory system in GAS. H uman bacterial pathogens, including Neisseria meningitidis(1), Staphylococcus aureus (2), Streptococcus pneumoniae (3), and Streptococcus pyogenes (group A Streptococcus [GAS]) (4), are frequently carried asymptomatically. However, in contrast to the relatively sophisticated knowledge regarding how bacterial pathogens cause disease, we understand little of the processes used by bacteria to persist on mucosal surfaces in the absence of symptoms. Asymptomatic carriage by or colonization of a susceptible host is a key step in the development of a myriad of diseases caused by bacterial pathogens. Inhibiting the ability of a pathogen to colonize a host may severely hamper its ability to subsequently cause disease. For example, vaccination against S. pneumoniae reduces the potential for disease by interfering with the organism's ability to colonize mucosal surfaces (5). In contrast, no effective GAS vaccine exists, and the ability of current candidate GAS vaccine formulations to prevent colonization is unknown. Thus, enhancing our understanding of the mechanisms used to colonize human hosts is paramount to reducing the incidence of disease caused by bacterial pathogens.GAS is an ideal model organism for the study of bacterial asymptomatic carriage. GAS causes a broad range of diseases in humans, including s...

Objective: Overall and atherosclerosis-associated mortality is elevated in humans with very high HDL (high-density lipoprotein) cholesterol concentrations. Mice with a deficiency of the HDL receptor, Scarb1 (scavenger receptor class B type 1), are a robust model of this phenotype and exhibit several additional pathologies. We hypothesized that the previously reported high plasma concentration of free cholesterol (FC)–rich HDL in Scarb1 −/ − mice produces a state of high HDL-FC bioavailability that increases whole-body FC and dysfunction in multiple tissue sites. Approach and Results: The higher mol% FC in Scarb1 −/− versus WT (wild type) HDL (41.1 versus 16.0 mol%) affords greater FC bioavailability for transfer to multiple sites. Plasma clearance of autologous HDL-FC mass was faster in WT versus Scarb1 −/− mice. FC influx from Scarb1 −/− HDL to LDL (low-density lipoprotein) and J774 macrophages was greater (≈4×) than that from WT HDL, whereas FC efflux capacity was similar. The higher mol% FC of ovaries, erythrocytes, heart, and macrophages of Scarb1 −/− versus WT mice is associated with previously reported female infertility, impaired cell maturation, cardiac dysfunction, and atherosclerosis. The FC contents of other tissues were similar in the two genotypes, and these tissues were not associated with any overt pathology. In addition to the differences between WT versus Scarb1 −/− mice, there were many sex-dependent differences in tissue-lipid composition and plasma FC clearance rates. Conclusions: Higher HDL-FC bioavailability among Scarb1 −/− versus WT mice drives increased FC content of multiple cell sites and is a potential biomarker that is mechanistically linked to multiple pathologies.