Role of putative virulence factors of Streptococcus pyogenes in mouse models of long-term throat colonization and pneumonia

Abstract

To investigate the role of putative virulence factors of Streptococcus pyogenes (group A streptococcus; GAS) in causing disease, we introduced specific mutations in GAS strain B514, a natural mouse pathogen, and tested the mutant strains in two models of infection. To study late stages of disease, we used our previously described mouse model (C3HeB/FeJ mice) in which pneumonia and systemic spread of the streptococcus follow intratracheal inoculation. To study the early stages of disease, we report here a model of long-term (at least 21 days) throat colonization following intranasal inoculation of C57BL/10SnJ mice. When the three emm family genes of GAS strain B514-Sm were deleted, the mutant showed no significant difference from the wild type in induction of long-term throat colonization or pneumonia. We inactivated the scpA gene, which encodes a complement C5a peptidase, by insertion of a nonreplicative plasmid and found no significant difference from the wild type in the incidence of throat colonization. However, there was a small but statistically significant decrease in the incidence of pneumonia caused by the scpA mutant. Finally, we demonstrated a very important effect of the hyaluronic acid capsule in both models. Following intranasal inoculation of mice with a mutant in which a nonreplicative plasmid was inserted into the hasA gene, which encodes hyaluronate synthase, we found that all bacteria recovered from the throats of the mice were encapsulated revertants. Following intratracheal inoculation with the hasA mutant, the incidence of pneumonia within 72 h was significantly reduced from that of the control strain (P ‫؍‬ 0.006). These results indicate that the hyaluronic acid capsule of S. pyogenes B514 confers an important selective advantage for survival of the bacteria in the upper respiratory tract and is also an important determinant in induction of pneumonia in our model system.

NAD+‐glycohydrolase acts as an intracellular toxin to enhance the extracellular survival of group A streptococci

“…The capacity of GAS to cause infection of the pharynx or other sites is related to the expression of several proven or suspected virulence determinants. M protein and the hyaluronic acid capsule are the two factors that have been shown most clearly to play an essential role in GAS infection (Hollingshead et al, 1993;Husmann et al, 1997;Moses et al, 1997;Ashbaugh et al, 1998;. Both are prominent structures on the bacterial surface, and each has been shown to confer resistance to complement-mediated phagocytic killing (Jacks-Weis et al, 1982;Whitnack and Beachey, 1982;Horstmann et al, 1988;Perez-Casal et al, 1993;Dale et al, 1996;Moses et al, 1997).…”

Role of Streptolysin O in a Mouse Model of Invasive Group A Streptococcal Disease

“…When animal models were used to examine strains carrying revertible mutations in genes whose products were important for virulence, selective pressure for expression of the virulence factor within the animal led to extensive reversion of the mutation. This has been reported for mutants in the synthesis of the hyaluronic acid capsule and the M protein in mouse models of pneumonia and invasive disease (3,19). Mutants in these factors were attenuated for virulence and were efficiently cleared by the mice, and bacteria recovered from infected animals had reverted to the wild type.…”

Virulence factors of the group A streptococci and genes that regulate their expression

“…However, the exact role and importance in virulence is difficult to ascertain. Husmann et al suggested that the contribution of C5a peptidase might be strain dependent as they were unable to find a difference between mutant and wild type strains in their ability to colonize the throat or to cause pneumonia in mice (89). Evidence that C5a peptidase plays a role in virulence includes the increased clearance from subdermal infection sites and nasopharyngeal mucosa in scpA mutants and a strong antibody response to the protein in adults but not in uninfected children (88,90,91).…”

“…One of the early proposed roles was to protect the organism from toxic oxygen metabolites by shielding the organism from oxygen by creating a barrier around the cell (92). However, more important functions of the capsule are its role in colonization, phagocytic killing, and infection (89,(93)(94)(95)(96). The capsule is involved in attachment to receptors on epithelial cells by binding to CD44, a hyaluronate-binding protein (97); such binding can induce cytoskeleton changes which can lead to cellular invasion (98).…”