Contribution of Urease to Colonization by Shiga Toxin-Producing Escherichia coli

Abstract

Shiga toxin-producing Escherichia coli (STEC) is a food-borne pathogen with a low infectious dose that colonizes the colon in humans and can cause severe clinical manifestations such as hemolytic-uremic syndrome. The urease enzyme, encoded in the STEC chromosome, has been demonstrated to act as a virulence factor in other bacterial pathogens. The NH 3 produced as urease hydrolyzes urea can aid in buffering bacteria in acidic environments as well as provide an easily assimilated source of nitrogen that bacteria can use to gain a metabolic advantage over intact microflora. Here, we explore the role of urease in STEC pathogenicity. The STEC urease enzyme exhibited maximum activity near neutral pH and during the stationary-growth phase. Experiments altering growth conditions performed with three phylogenetically distinct urease-positive strains demonstrated that the STEC ure gene cluster is inducible by neither urea nor pH but does respond to nitrogen availability. Quantitative reverse transcription-PCR (qRT-PCR) data indicate that nitrogen inhibits the transcriptional response. The deletion of the ure gene locus was constructed in STEC strain 88-0643, and the ure mutant was used with the wild-type strain in competition experiments in mouse models to examine the contribution of urease. The wild-type strain was twice as likely to survive passage through the acidic stomach and demonstrated an enhanced ability to colonize the intestinal tract compared to the ure mutant strain. These in vivo experiments reveal that, although the benefit STEC gains from urease expression is modest and not absolutely required for colonization, urease can contribute to the pathogenicity of STEC. Shiga toxin-producing Escherichia coli (STEC) is an enteric pathogen that colonizes the colon in humans and causes a variety of symptoms ranging from mild diarrhea to bloody diarrhea or the more severe renal pathology of hemolytic uremic syndrome, sometimes followed by death (17). In the first two STEC genomes sequenced, those of the O157:H7 EDL933 strain and O157:H7 Sakai strain, a genomic island containing, among other genes, ureDABCEFG, a cluster of genes coding for the enzyme urease and its accessory proteins, was identified (12, 39). Subsequently, many other STEC strains, including a wide variety of serotypes, have been found to carry the ure gene cluster (9,35,36,46). Urease, which hydrolyzes the substrate urea to form CO 2 and two molecules of NH 3 (29), has been demonstrated to contribute to virulence in several other bacterial species (1, 5-8, 25, 43). The NH 3 produced raises the pH of the cytoplasm, thereby buffering the bacteria under acidic environmental conditions. In addition, the NH 3 provides the bacterial cell with an easily assimilated source of nitrogen. Despite the fact that STEC has been recognized as an emergent pathogen since 1982 (42), virtually no information about the regulation of the ure genes and how they contribute to pathogenicity in this important pathogen is available.Neither STEC strain EDL933 nor the Sakai strain...

Molecular Hazard Identification of Non-O157 Shiga Toxin-Producing Escherichia coli (STEC)

“…Mutation of this gene resulted in reduced adherence of E . coli O157:H7 in ligated pig intestine [ 38 ] and strains with nonfunctional urease were less likely to survive stomach passage and colonize the mouse intestinal tract compared to urease positive strains [ 39 ]. However, in other studies ureC was strongly correlated to intimin [ 22 , 37 ].…”

Ureases: Historical aspects, catalytic, and non-catalytic properties – A review

“…Reduction of the ureolytic bacteria load and the use of acetohydroxamic acid as a urease inhibitor are considered therapeutic approaches under these conditions [119] , [120] , [121] . Other pathogens also produce urease to acquire acid resistance and enable colonization, among which are Shiga-toxin producing Escherichia coli [122] , Yersinia enterocolitica [123] , K. pneumoniae [124] , Brucella abortus [125] , and Haemophilus influenza [126] . Fungal ureases are involved in the pathogenesis of human cryptococcosis by Cryptococcus neoformans [127] , [128] , and Cryptococcus gattii [35] , and of coccidiodomycosis (San Joaquin Valley fever) by Coccidioides immitis and C. posadasii [37] .…”

From food to cell: nutrient exploitation strategies of enteropathogens

“…Bacillus cereus, Clostridium perfringens, Yersinia enterocolitica, Vibrio parahaemolyticus and enterohaemorrhagic E. coli (EHEC), harbour genes encoding ureolytic activities (Table 1). So far, urease has only been demonstrated to play a role in gut colonization by Shiga toxin-producing E. coli (Steyert & Kaper, 2012) and it remains to be investigated to what extent ureases contribute to improved nitrogen availability of other enteric pathogens.…”