Role of YadA, Ail and Lipopolysaccharide in Serum Resistance of Yersinia enterocolitica Serotype O:3

Biedzka‐Sarek, M.; Venho, R.; Skurnik, M.

Complement attack is one of the host strategies leading to elimination of pathogens. Yersinia enterocolitica, resistant to human serum, expresses several factors that may contribute to this resistance, the outer membrane proteins YadA and Ail, and lipopolysaccharide (LPS). To study relative roles of these factors for the survival of Y. enterocolitica serotype, O:3 (Ye O:3) in nonimmune human serum, we constructed 23 mutant strains of Ye O:3 expressing different combinations of YadA, Ail, LPS O‐antigen and LPS outer core. Survival of bacteria was analysed in normal serum (with functional classical and alternative complement activation pathways) and EGTA‐Mg‐treated serum (only alternative pathway functional). Kinetic killing tests revealed that the most potent single serum resistance factor needed for long‐term survival was YadA. Ail was important for short‐term survival and thus delayed the bacterial killing. On the contrary, the LPS O‐antigen and outer core when in combination with YadA or Ail, or both, had a minor and often negative effect on serum resistance.