Abstract
Enterohaemorrhagic Escherichia coli (EHEC) are responsible for outbreaks of food- and water-borne illness. The bovine gastrointestinal tract (GIT) is thought to be the principle reservoir of EHEC. Knowledge of the nutrients essential for EHEC growth and survival in the bovine intestine may help in developing strategies to limit their shedding in bovine faeces thus reducing the risk of human illnesses. To identify specific metabolic pathways induced in the animal GIT, the transcriptome profiles of EHEC O157:H7 EDL933 during incubation in bovine small intestine contents (BSIC) and minimal medium supplemented with glucose were compared. The transcriptome analysis revealed that genes responsible for the assimilation of ethanolamine, urea, agmatine and amino acids (Asp, Thr, Gly, Ser and Trp) were strongly up-regulated suggesting that these compounds are the main nitrogen sources for EHEC in BSIC. A central role for the gluconeogenesis pathway and assimilation of gluconeogenic substrates was also pinpointed in EHEC incubated in BSIC. Our results suggested that three amino acids (Asp, Ser and Trp), glycerol, glycerol 3-phosphate, L-lactate and C4-dicarboxylates are important carbon sources for EHEC in BSIC. The ability to use gluconeogenic substrates as nitrogen sources (amino acids) and/or carbon sources (amino acids, glycerol and lactate) may provide a growth advantage to the bacteria in intestinal fluids. Accordingly, aspartate (2.4 mM), serine (1.9 mM), glycerol (5.8 mM) and lactate (3.6 mM) were present in BSIC and may represent the main gluconeogenic substrates potentially used by EHEC. A double mutant of E. coli EDL933 defective for phosphoenolpyruvate synthase (PpsA) and phosphoenolpyruvate carboxykinase (PckA), unable to utilize tricarboxylic acid (TCA) intermediates was constructed. Growth competition experiments between EHEC EDL933 and the isogenic mutant strain in BSIC clearly showed a significant competitive growth advantage of the wild-type strain further illustrating the importance of the gluconeogenesis pathway in maintaining EHEC in the bovine GIT.
Highlights
Enterohaemorrhagic Escherichia coli (EHEC) are Shiga toxinproducing E. coli (STEC) responsible for human gastrointestinal illnesses, including bloody diarrhea [1]
Microarray technology was used to identify global gene expression changes in EHEC EDL933 grown in bovine small intestine contents (BSIC), relative to the same strain grown in minimal M9 medium supplemented with glucose as the sole carbon source (M9-Glc)
Since the aim of this report was to increase our understanding of the nutritional basis of EHEC survival in the bovine intestine, we focused on genes up-regulated in EHEC EDL933 incubated in BSIC encoding the transport and metabolism of carbon and nitrogen sources
Summary
Enterohaemorrhagic Escherichia coli (EHEC) are Shiga toxinproducing E. coli (STEC) responsible for human gastrointestinal illnesses, including bloody diarrhea [1]. These disorders may be complicated by renal dysfunction, including the life-threatening haemolytic-uraemic syndrome (HUS), responsible for acute renal failure in children [2]. While EHEC strains colonize the bovine gastrointestinal tract, cattle are asymptomatic because they do not express the globotriaosylceramide-3 (Gb3). Binding to this receptor is thought to be necessary for the pathophysiological effects associated with Shiga toxin in the human host [5]. EHEC strains are transmitted from cattle to humans by means of unpasteurized milk, undercooked meat, fruit, vegetables or water. Hides have been identified as the principal source of EHEC contamination during slaughter [6]
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