Proteus mirabilis strains of diverse type have IgA protease activity.

A strain of Proteus mirabilis associated with chronic urinary tract infection was found to produce an EDTA-sensitive IgA protease that cleaved the IgA heavy chain into two fragments at sites different from those attacked by other microbial IgA1 proteases. Another 14 P. mirabilis strains of diverse type and from various clinical conditions also produced a similar IgA protease. This enzyme may be a virulence determinant of P. mirabilis.