[ODP-150] Streptococcus gordonii DL1 survives PMNs killing through its resistance to lysozyme
Objectives: Streptococcus gordonii is an etiological bacterial agent of infective endocarditis. Although the pathogenesis mechanisms are not well understood, we think that the resistance to phagocytes is important for the development of infective endocarditis. Previous studies showed that S. gordonii DL1 survived in the phagolysosomes of polymorphonuclear leukocytes (PMNs), whereas S. gordonii SK12 was sensitive to PMN-dependent killing. In this study, we investigated the resistant factors of S. gordonii DL1 to the PMN-dependent killing.
Methods: Human PMNs were used for the PMN-dependent killing. Hydrogen peroxide, lysozyme, defensin, and lactoferrin were used as the bactericidal agents. As mature phagolysosomes are acidic, the effects of low pH were also investigated. The survival of S. gordonii strains was assessed by a colony-forming assay.
Results: S. gordonii DL1 survived the PMN-dependent killing longer than SK12. Nevertheless, DL1 was more sensitive to hydrogen peroxide than SK12. Both strains showed the similar resistance to the low pH conditions and to the bactericidal agents used at pH 7.0. Importantly, at pH 5.0, SK12 was turned to sensitive to the bactericidal agents, especially lysozyme, while SK12 was not.
Conclusion: These results indicated that S. gordonii DL1 is resistant to lysozyme in the acidic condition, which is similar with the inside of phagolysosomes.