Involvement of the accessory gene regulator (agr) in expression of type 5 capsular polysaccharide by Staphylococcus aureus.

The effect of an agr mutation on expression of type 5 capsular polysaccharide (CP) by Staphylococcus aureus Newman was investigated in different complex and synthetic media. CP expression by the agr mutant was strongly reduced in certain media but slightly in others, indicating that CP synthesis is positively controlled by agr. CP expression occurred in the post-exponential growth phase in both wild-type and mutant strains, suggesting that other regulatory systems could act in conjunction with agr.