Previous Article | Next Article ![]()
Infect. Immun., 01 1997, 64-71, Vol 65, No. 1
AE Moses, MR Wessels, K Zalcman, S Alberti, S Natanson-Yaron, T Menes and E Hanski
The antiphagocytic effect of M protein has been considered a critical
element in virulence of the group A streptococcus. The hyaluronic acid
capsule also appears to play an important role: studies of an acapsular
mutant derived from the mucoid or highly encapsulated M protein type 18
group A streptococcal strain 282 indicated that loss of capsule expression
was associated with decreased resistance to phagocytic killing and with
reduced virulence in mice. To study directly the relative contributions to
virulence of M protein and the hyaluronic acid capsule in strain 282, we
inactivated the gene encoding the M protein (emm18) both in wild-type
strain 282 and in its acapsular mutant, strain TX72. Inactivation of emm18
was accomplished by integrational plasmid mutagenesis, using the
temperature-sensitive shuttle vector pJRS233 harboring a 5' DNA segment of
emm18. As reported previously, wild-type strain 282 was resistant to
phagocytic killing in vitro, both in whole human blood and in 10% serum.
The capsule mutant TX72 was highly susceptible to phagocytic killing in 10%
serum and moderately sensitive in whole blood. The M protein mutant 282KZ
was highly susceptible to phagocytic killing in blood but only moderately
sensitive in 10% serum. The double mutant TX74 was sensitive to killing in
both conditions. In a mouse infection model, the 50% lethal dose was
increased by 60- and 80-fold for the capsule and double mutants,
respectively, compared with that of strain 282, but only by 6-fold for the
M protein mutant. Integration of the strain 282 capsule genes into the
chromosome of a nonmucoid M1 strain resulted in high-level capsule
production and rendered the transformed strain resistant to phagocytic
killing in 10% serum. These results provide further evidence that the
hyaluronic acid capsule confers resistance to phagocytosis and enhances
group A streptococcal virulence. The results suggest also that assessment
of in vitro resistance to phagocytosis in 10% serum rather than in whole
blood may be a more accurate reflection of virulence in vivo of group A
streptococci.
Copyright © 1997, American Society for Microbiology
Relative contributions of hyaluronic acid capsule and M protein to virulence in a mucoid strain of the group A Streptococcus
Department of Clinical Microbiology and Infectious Disease, Hadassah University Hospital, Jerusalem, Israel. MOSESA@md2.huji.ac.il
This article has been cited by other articles:
| J. Bacteriol. | J. Virol. | Eukaryot. Cell |
|---|
| Microbiol. Mol. Biol. Rev. | Clin. Vaccine Immunol. | All ASM Journals |
|---|