Abstract
The present study tested whether exposure of enterotoxigenic Escherichia coli (ETEC) to glucose at different concentrations in the media results in increased bacterial adherence to host cells through increased heat-labile enterotoxin (LT) production, thereby suggesting the effects are physiological. Porcine-origin ETEC strains grown in Casamino acid yeast extract medium containing different concentrations of glucose were washed and inoculated onto IPEC-J2 porcine intestinal epithelial cells to test for effects on adherence and host cell cAMP concentrations. Consistent with previous studies, all LT+ strains had higher ETEC adherence to IPEC-J2 cells than did LT− strains. Adherence of the LT− but not the LT+ strains was increased by pre-incubating the IPEC-J2 cells with LT and decreased by co-incubation with GM1 ganglioside in a dose-dependent manner (P<0.05). To determine whether the glucose concentration of the cell culture media has an effect on adherence, IPEC-J2 cells were inoculated with LT+ or LT− strains in cell culture media containing a final glucose concentration of 0, 0.25, 0.5, 1.0 or 2.0%, and incubated for 4 h. Only media containing 0.25% glucose resulted in increased adherence and cAMP levels, and this was limited to IPEC-J2 cells inoculated with LT+ strains. This study supports the hypothesis that glucose, at a concentration optimal for LT expression, enhances bacterial adherence through the promotion of LT production. Hence, these results establish the physiological relevance of the effects of glucose on LT production and provide a basis for how glucose intake may influence the severity of ETEC infection.
Highlights
Enterotoxigenic Escherichia coli (ETEC) is the most common bacterial cause of diarrhea in humans in the world [1] and an important cause of diarrhea and death in livestock, especially cattle and swine [2], [3]
Many highly virulent enterotoxigenic Escherichia coli (ETEC) isolates from swine produce F4ac (K88ac) fimbria and both heat-labile enterotoxin-I (LT) and heat-stable enterotoxin-b (STb) [5], with the genes for the two toxins linked on a large, transmissible plasmid [6]
Bacterial strains and culture conditions The following strains were used in this study: 2534-86, a wildtype (WT) porcine-origin F4ac+, LT+, STb+ ETEC [19]; WAM2317, a spontaneous nalidixic-acid resistant mutant of 2534-86 [19]; MUN297 (STb2 mutant of WAM2317); MUN298 (MUN297 complemented with STb); MUN299 (LT2 mutant of WAM2317); MUN300 (LT2 STb2 mutant of WAM2317); and MUN301 (MUN300 complemented with LT) [14]
Summary
Enterotoxigenic Escherichia coli (ETEC) is the most common bacterial cause of diarrhea in humans in the world [1] and an important cause of diarrhea and death in livestock, especially cattle and swine [2], [3]. Many highly virulent ETEC isolates from swine produce F4ac (K88ac) fimbria and both heat-labile enterotoxin-I (LT) and heat-stable enterotoxin-b (STb) [5], with the genes for the two toxins linked on a large, transmissible plasmid [6]. Environmental conditions are known to affect the production of LT, heat stable enterotoxin-a (STa) and STb [7], [8], [9], [10], [11]. Glucose increases LT production through de-repression of the eltAB (LT) promoter [12]. Glucose suppresses synthesis of cyclic AMP (cAMP), which prevents cAMP receptor protein (CRP)-cAMP complex formation and binding to sites upstream and within the eltA promoter [12]. Glucose prevents transcription of estB (STb) and estA (STa) through catabolite repression [10], [12]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
