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Applied and Environmental Microbiology, October 2007, p. 6351-6359, Vol. 73, No. 20
0099-2240/07/$08.00+0     doi:10.1128/AEM.00920-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

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

Institute for Hygiene and the National Consulting Laboratory on Hemolytic Uremic Syndrome, University of Münster, Robert Koch Strasse 41, 48149 Münster, Germany,¹ National Reference Center for Salmonella and Other Enteric Pathogens, Robert Koch Institute, Branch Wernigerode, Burgstrasse 37, 38855 Wernigerode, Germany,² Institute for Food Chemistry, University of Münster, Correnstrasse 45, 48149 Münster, Germany³

Received 24 April 2007/ Accepted 5 August 2007

We investigated the prevalence, distribution, and structure of espP in Shiga toxin-producing Escherichia 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-bp espP gene distinguished four alleles (espP, espPß, espP, and espP), with 99.9%, 99.2%, 95.3%, and 95.1% homology, respectively, to espP of E. coli O157:H7 strain EDL933. The espPß, espP, and espP genes contained unique insertions and/or clustered point mutations that enabled allele-specific PCRs; these demonstrated the presence of espP, espPß, espP, and espP in STEC isolates belonging to 17, 16, 15, and 8 serotypes, respectively. Among four subtypes of EspP encoded by these alleles, EspP (produced by enterohemorrhagic E. coli [EHEC] O157:H7 and the major non-O157 EHEC serotypes) and EspP cleaved pepsin A, human coagulation factor V, and an oligopeptide alanine-alanine-proline-leucine-para-nitroaniline, whereas EspPß and EspP either were not secreted or were proteolytically inactive. The lack of proteolysis correlated with point mutations near the active serine protease site. We conclude that espP 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.

Published ahead of print on 17 August 2007.

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