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Enhanced phagocytosis of group A streptococci M type 6 by oleic acid
Abstract:
M protein, located on the surface fimbriae of group A streptococci, is antiphagocytic by unknown means. It is known that oleic acid kills group A streptococci and distorts the fimbriae. The effect of oleic acid on phagocytosis of group A streptococci was examined. Phagocytosis of a strain possessing M protein (M+) and its M- variant was assessed by uptake of radiolabeled bacteria and by chemiluminescence. The M- but not the M+ streptococci were well phagocytized and induced chemiluminescence. Oleic acid-killed and heat-killed streptococci (both M+ and M-) were readily phagocytized and induced sustained chemiluminescence. M+ streptococci killed by ultraviolet irradiation were inefficiently phagocytized and did not induce chemiluminescence. Oleic acid-killed M+ streptococci absorbed type-specific antibody. An extract of M protein reduced the bactericidal capacity of oleic acid. It is proposed that oleic acid may bind to and alter the M protein of group A streptococci and thereby enhance phagocytosis.
Insights
Oleic acid enhances the immune system's ability to clear group A streptococci. This fatty acid may alter the bacteria's M protein, making them more susceptible to phagocytosis.
Area of Science:
- Microbiology
- Immunology
- Bacteriology
Background:
- Group A streptococci possess M protein on fimbriae, conferring antiphagocytic properties through unknown mechanisms.
- Oleic acid is known to be bactericidal against group A streptococci and to distort their fimbriae.
Purpose of the Study:
- To investigate the effect of oleic acid on the phagocytosis of group A streptococci.
- To determine if oleic acid can overcome the antiphagocytic properties of M protein.
Main Methods:
- Assessed phagocytosis via radiolabeled bacteria uptake and chemiluminescence.
- Compared phagocytosis of M+ and M- strains of group A streptococci.
- Examined the effect of various killing methods (oleic acid, heat, UV) on phagocytosis.
Main Results:
- M- variants were readily phagocytized, unlike M+ strains.
- Oleic acid-killed M+ and M- streptococci were efficiently phagocytized.
- UV-killed M+ streptococci were poorly phagocytized.
- Oleic acid-killed M+ streptococci absorbed type-specific antibody, and M protein extract reduced oleic acid's bactericidal effect.
Conclusions:
- Oleic acid may enhance phagocytosis of group A streptococci by binding to and altering M protein.
- This alteration potentially renders the bacteria more susceptible to immune clearance mechanisms.