Subtypes of the Plasmid-Encoded Serine Protease EspP in Shiga Toxin-Producing Escherichia coli : Distribution, Secretion, and Proteolytic Activity

We investigated the prevalence, distribution, and structure ofespP in Shiga toxin-producingEscherichia coli (STEC) and assessed the secretion and proteolytic activity of the encoded autotransporter protein EspP (extracellular serine protease, plasmid encoded).espP was identified in 56 of 107 different STEC serotypes. Sequencing of a 3,747-bp region of the 3,900-bpespP gene distinguished four alleles (espP α,espP β,espP γ, andespP δ), with 99.9%, 99.2%, 95.3%, and 95.1% homology, respectively, toespP ofE. coli O157:H7 strain EDL933. TheespP β,espP γ, andespP δ genes contained unique insertions and/or clustered point mutations that enabled allele-specific PCRs; these demonstrated the presence ofespP α,espP β,espP γ, andespP δ in STEC isolates belonging to 17, 16, 15, and 8 serotypes, respectively. Among four subtypes of EspP encoded by these alleles, EspPα (produced by enterohemorrhagicE. coli [EHEC] O157:H7 and the major non-O157 EHEC serotypes) and EspPγ cleaved pepsin A, human coagulation factor V, and an oligopeptide alanine-alanine-proline-leucine-para-nitroaniline, whereas EspPβ and EspPδ either were not secreted or were proteolytically inactive. The lack of proteolysis correlated with point mutations near the active serine protease site. We conclude thatespP is widely distributed among STEC strains and displays genetic heterogeneity, which can be used for subtyping and which affects EspP activity. The presence of proteolytically active EspP in EHEC serogroups O157, O26, O111, and O145, which are bona fide human pathogens, suggests that EspP might play a role as an EHEC virulence factor.