Staphylococcal protein A inflames the lungs

Prevalence of virulence factors in Staphylococcus intermedius isolates from dogs and pigeons

Background

Staphylococcus intermedius has been isolated from healthy dogs and pigeons as well as diseased dogs. Similar to Staphylococcus aureus, S. intermedius is known to carry many virulence factors but most of these factors remain to be studied. In this study, we examined 106 S. intermedius isolates (44 dog isolates and 62 pigeon isolates) for their hemolytic activity, biofilm formation, protease activity, and clumping factor and protein A production.

Results

Forty-three dog isolates (97.7%) and all pigeon isolates were hemolytic on sheep RBCs with a mean hemolytic titer of 336.7 and 47.32, respectively, whereas 43 dog isolates (97.7%) and 11 pigeon isolates (17.7%) exhibited a significant difference in their hemolytic activity on rabbit RBCs with a mean hemolytic titer of 11.04 and 3.76, respectively (p < 0.0005). The mean biofilm formation activity for dog isolates was 0.49, which was significantly higher than that (0.33) for pigeon isolates (p < 0.0005). Twenty-four dog isolates (54.5%) and 11 pigeon isolates (17.7%) were protease positive. Twenty-four dog isolates (54.5%) were clumping factor- and protein A- positive.

Conclusion

S. intermedius strains carrying the virulence factors examined in this study were more prevalent in dogs than pigeons.

Recognition of Staphylococcus aureus by the innate immune system

The gram-positive bacterium Staphylococcus aureus is a major pathogen responsible for a variety of diseases ranging from minor skin infections to life-threatening conditions such as sepsis. Cell wall-associated and secreted proteins (e.g., protein A, hemolysins, and phenol-soluble modulin) and cell wall components (e.g., peptidoglycan and alanylated lipoteichoic acid) have been shown to be inflammatory, and these staphylococcal components may contribute to sepsis. On the host side, many host factors have been implicated in the innate detection of staphylococcal components. One class of pattern recognition molecules, Toll-like receptor 2, has been shown to function as the transmembrane component involved in the detection of staphylococcal lipoteichoic acid and phenol-soluble modulin and is involved in the synthesis of inflammatory cytokines by monocytes/macrophages in response to these components. Nod2 (nucleotide-binding oligomerization domain 2) is the intracellular sensor for muramyl dipeptide, the minimal bioactive structure of peptidoglycan, and it may contribute to the innate immune defense against S. aureus. The staphylococcal virulence factor protein A was recently shown to interact directly with tumor necrosis factor receptor 1 in airway epithelium and to reproduce the effects of tumor necrosis factor alpha. Finally, peptidoglycan recognition protein L is an amidase that inactivates the proinflammatory activities of peptidoglycan. However, peptidoglycan recognition protein L probably plays a minor role in the innate immune response to S. aureus. Thus, several innate immunity receptors may be implicated in host defense against S. aureus.