Alpha-toxin and gamma-toxin jointly promote Staphylococcus aureus virulence in murine septic arthritis

Abstract

Septic arthritis is a common and feared complication of staphylococcal infections. Staphylococcus aureus produces a number of potential virulence factors including certain adhesins and enterotoxins. In this study we have assessed the roles of cytolytic toxins in the development of septic arthritis by inoculating mice with S. aureus wild-type strain 8325-4 or isogenic mutants differing in the expression of alpha-, beta-, and gamma-toxin production patterns. Mice inoculated with either an alpha- or beta-toxin mutant showed degrees of inflammation, joint damage, and weight decrease similar to wild-type-inoculated mice. In contrast, mice inoculated with either double (alpha- and gamma-toxin-deficient)- or triple (alpha-, beta-, and gamma-toxin-deficient)-mutant S. aureus strains showed lower frequency and severity of arthritis, measured both clinically and histologically, than mice inoculated with the wild-type strain. We conclude that simultaneous production of alpha- and gamma-toxin is a virulence factor in S. aureus arthritis.

FIG. 1

Frequency of arthritis after inoculation with 2 × 10⁷ to 3 × 10⁷ CFU of S. aureus wild-type strain 8325-4 Hla⁺ Hlb⁺ Hlg⁺ (n = 15) or its isogenic triple-mutant, DU5938 Hla⁻ Hlb⁻ Hlg⁻ (n = 15).

FIG. 2

Changes in body weight of mice after inoculation with S. aureus wild-type strain 8325-4 Hla⁺ Hlb⁺ Hlg⁺ or any of its isogenic mutants differing in hemolysin secretion patterns (12 or 13 in each group). c, the Hla⁺ Hlb⁻ Hlg⁺ strain complemented with the wild-type hlg gene. P values refer to comparisons with the wild-type strain. N.S., not significant.

FIG. 3

Histopathological changes in joints of NMRI mice inoculated with S. aureus wild-type strain 8325-4 Hla⁺ Hlb⁺ Hlg⁺ or its isogenic mutants DU5945 Hla⁻ Hlb⁺ Hlg⁻, DU5719 Hla⁺ Hlb⁻ Hlg⁺, or DU5938 Hla⁻ Hlb⁻ Hlg⁻. P values refer to comparison with the wild-type strain. N.S., not significant. Severe synovitis and erosivity equal scores of more than 2 points, as described in Materials and Methods.

FIG. 4

Levels of IL-6 in serum at 21 days after inoculation with 1.6 × 10⁸ CFU of either wild-type S. aureus 8325-4 Hla⁺ Hlb⁺ Hlg⁺ (n = 11), DU5938 Hla⁻ Hlb⁻ Hlg⁻ (n = 12), DU5945 Hla⁻ Hlb⁺ Hlg⁻ (n = 13), or DU5719 Hla⁺ Hlb⁻ Hlg⁺ (n = 11). P values refer to comparisons with the Hla⁺ Hlb⁺ Hlg⁺ wild-type strain. N.S., not significant.