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Increased sensitivity to phagocytosis of Staphylococcus E-46 after growth in artificial media
Abstract:
Staphylococcus E-46, which exhibits high virulence in mice mainly due to resistance to phagocytosis, gradually lost its virulence during growth in artificial media [Heart-Infusion (HI) slants]. Staphylococcus E-46 is coagulase-negative and DNase-positive, and has a capsule-like structure, and the less-virulent derivative (LVD) strain seemed not to be changed in this respect. The bacteria which had been exposed to HI slants for more than one year (= LVD strain) became more sensitive to phagocytosis by mouse peritoneal macrophages than bacteria which were kept in a lyophilized state. The chemiluminescent response of macrophages to the LVD strain was remarkably higher than that to the original Staphylococcus E-46. When the LVD or the sera for opsonization were heated, the chemiluminescence to the LVD was as low as that to the original Staphylococcus E-46. Polyacrylamide gel electrophoresis of sonication-released membrane protein from the LVD strain showed a unique band with a molecular weight of about 40,000. The factor concerned with the virulence of Staphylococcus E-46 is discussed based on these results.
Insights
Staphylococcus E-46 lost virulence and became more susceptible to phagocytosis after prolonged growth. This suggests a key virulence factor in Staphylococcus E-46 is heat-labile and associated with a 40,000 MW membrane protein.
Area of Science:
- Microbiology
- Immunology
- Bacterial Pathogenesis
Background:
- Staphylococcus E-46 exhibits high virulence in mice, primarily due to resistance to phagocytosis.
- The bacteria possess a capsule-like structure and are coagulase-negative and DNase-positive.
Purpose of the Study:
- To investigate the mechanisms behind the loss of virulence in Staphylococcus E-46 during prolonged in vitro cultivation.
- To identify factors contributing to the high virulence of the original Staphylococcus E-46 strain.
Main Methods:
- Cultivation of Staphylococcus E-46 on Heart-Infusion (HI) slants for over one year to generate a less-virulent derivative (LVD) strain.
- Assessment of phagocytosis sensitivity by mouse peritoneal macrophages.
- Measurement of macrophage chemiluminescent response.
- Heat treatment of LVD and opsonizing sera.
- Polyacrylamide gel electrophoresis (PAGE) of membrane proteins.
Main Results:
- The LVD strain showed increased sensitivity to phagocytosis compared to lyophilized bacteria.
- Macrophage chemiluminescence was significantly higher with the LVD strain, indicating enhanced immune recognition.
- Heating the LVD strain or sera abolished this enhanced chemiluminescence, suggesting a heat-labile factor.
- PAGE revealed a unique 40,000 MW membrane protein band in the LVD strain.
Conclusions:
- Prolonged growth in artificial media leads to a loss of virulence in Staphylococcus E-46, associated with increased phagocytosis susceptibility.
- A heat-labile factor, possibly the identified 40,000 MW membrane protein, is implicated in the virulence of Staphylococcus E-46.