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Relationship between heat-labile enterotoxin secretion capacity and virulence in wild type porcine-origin enterotoxigenic Escherichia coli strains.

Wijemanne P, Xing J, Berberov EM, Marx DB, Francis DH, Moxley RA - PLoS ONE (2015)

Bottom Line: Maximum Likelihood phylogenetic trees constructed using T2SS genes gspC, gspD, gspE and homologs showed that strains 2534-86 and 3030-2 clustered together in the same clade with other porcine-origin ETEC strains in the database, UMNK88 and UMN18.Protein modeling of the ATPase gene (gspE) further revealed a direct relationship between the predicted ATP-binding capacities and LT secretion levels as follows: H10407, -8.8 kcal/mol and 199 ng/ml; 3030-2, -8.6 kcal/mol and 133 ng/ml; and 2534-86, -8.5 kcal/mol and 80 ng/ml.This study demonstrated a direct relationship between predicted ATP-binding capacity of GspE and LT secretion, and between the latter and virulence.

View Article: PubMed Central - PubMed

Affiliation: School of Veterinary Medicine and Biomedical Sciences, University of Nebraska-Lincoln, Lincoln, Nebraska, United States of America.

ABSTRACT
Heat-labile enterotoxin (LT) is an important virulence factor secreted by some strains of enterotoxigenic Escherichia coli (ETEC). The prototypic human-origin strain H10407 secretes LT via a type II secretion system (T2SS). We sought to determine the relationship between the capacity to secrete LT and virulence in porcine-origin wild type (WT) ETEC strains. Sixteen WT ETEC strains isolated from cases of severe diarrheal disease were analyzed by GM1ganglioside enzyme-linked immunosorbent assay to measure LT concentrations in culture supernatants. All strains had detectable LT in supernatants by 2 h of culture and 1 strain, which was particularly virulent in gnotobiotic piglets (3030-2), had the highest LT secretion level all porcine-origin WT strains tested (P<0.05). The level of LT secretion (concentration in supernatants at 6-h culture) explained 92% of the variation in time-to-a-moribund-condition (R2 = 0.92, P<0.0001) in gnotobiotic piglets inoculated with either strain 3030-2, or an ETEC strain of lesser virulence (2534-86), or a non-enterotoxigenic WT strain (G58-1). All 16 porcine ETEC strains were positive by PCR analysis for the T2SS genes, gspD and gspK, and bioinformatic analysis of 4 porcine-origin strains for which complete genomic sequences were available revealed a T2SS with a high degree of homology to that of H10407. Maximum Likelihood phylogenetic trees constructed using T2SS genes gspC, gspD, gspE and homologs showed that strains 2534-86 and 3030-2 clustered together in the same clade with other porcine-origin ETEC strains in the database, UMNK88 and UMN18. Protein modeling of the ATPase gene (gspE) further revealed a direct relationship between the predicted ATP-binding capacities and LT secretion levels as follows: H10407, -8.8 kcal/mol and 199 ng/ml; 3030-2, -8.6 kcal/mol and 133 ng/ml; and 2534-86, -8.5 kcal/mol and 80 ng/ml. This study demonstrated a direct relationship between predicted ATP-binding capacity of GspE and LT secretion, and between the latter and virulence.

No MeSH data available.


Related in: MedlinePlus

Linear regression between heat-labile enterotoxin (LT) secretion in culture and h to a moribund condition in gnotobiotic piglets inoculated with the corresponding E. coli strain.Concentration of LT in supernatants of 6-h cultures of strains G58–1 (LT-), 2534–86 (LT+), and 3030–2 (LT+; data shown in Fig. 1) and h-to-a-moribund-condition in piglets after inoculation with the same strains was used in the regression analysis.
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pone.0117663.g003: Linear regression between heat-labile enterotoxin (LT) secretion in culture and h to a moribund condition in gnotobiotic piglets inoculated with the corresponding E. coli strain.Concentration of LT in supernatants of 6-h cultures of strains G58–1 (LT-), 2534–86 (LT+), and 3030–2 (LT+; data shown in Fig. 1) and h-to-a-moribund-condition in piglets after inoculation with the same strains was used in the regression analysis.

Mentions: Gnotobiotic piglets inoculated with strains 3030–2 or 2534–86 had an onset of diarrhea at 6 or 12 h PI, respectively, with subsequent passage of watery, clear-yellow fecal material. All piglets inoculated with strain 3030–2 or 2534–86 rapidly developed severe weight loss and dehydration, and became moribund; however, the clinical course with 3030–2 was more rapid. The mean time-to-a-moribund-condition with 3030–2 was 14.4 h PI, in contrast to 71.2 h PI for 2534–86 (P<0.001). Hence, among these 2 strains, 3030–2 was significantly more virulent. Non-enterotoxigenic strain G58–1 did not induce clinical illness, and piglets inoculated with this strain were euthanized at 96 h PI since their survival time would have been indefinite. A linear regression between LT secretion at 6 h of culture for these 3 strains and h-to-a-moribund-condition in inoculated gnotobiotic piglets was conducted. The model-adjusted coefficient of determination (R2) was 0.92 (P < 0.0001), indicating that approximately 92% of the variation in the time-to-a-moribund condition could be explained by the LT secretion level of the inoculum strain (Fig. 3). A second linear regression based on LT concentrations at 18 h of culture yielded a model-adjusted R2 of 0.8842 (P < 0.0001). This lower R2 value supported the hypothesis by Lasaro et al. [21] that virulence is more highly correlated with secretion than total production of LT, since a portion of the LT activity in the supernatants from 18 h cultures originated from lysed cells in the stationary-to-death phases.


Relationship between heat-labile enterotoxin secretion capacity and virulence in wild type porcine-origin enterotoxigenic Escherichia coli strains.

Wijemanne P, Xing J, Berberov EM, Marx DB, Francis DH, Moxley RA - PLoS ONE (2015)

Linear regression between heat-labile enterotoxin (LT) secretion in culture and h to a moribund condition in gnotobiotic piglets inoculated with the corresponding E. coli strain.Concentration of LT in supernatants of 6-h cultures of strains G58–1 (LT-), 2534–86 (LT+), and 3030–2 (LT+; data shown in Fig. 1) and h-to-a-moribund-condition in piglets after inoculation with the same strains was used in the regression analysis.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4358887&req=5

pone.0117663.g003: Linear regression between heat-labile enterotoxin (LT) secretion in culture and h to a moribund condition in gnotobiotic piglets inoculated with the corresponding E. coli strain.Concentration of LT in supernatants of 6-h cultures of strains G58–1 (LT-), 2534–86 (LT+), and 3030–2 (LT+; data shown in Fig. 1) and h-to-a-moribund-condition in piglets after inoculation with the same strains was used in the regression analysis.
Mentions: Gnotobiotic piglets inoculated with strains 3030–2 or 2534–86 had an onset of diarrhea at 6 or 12 h PI, respectively, with subsequent passage of watery, clear-yellow fecal material. All piglets inoculated with strain 3030–2 or 2534–86 rapidly developed severe weight loss and dehydration, and became moribund; however, the clinical course with 3030–2 was more rapid. The mean time-to-a-moribund-condition with 3030–2 was 14.4 h PI, in contrast to 71.2 h PI for 2534–86 (P<0.001). Hence, among these 2 strains, 3030–2 was significantly more virulent. Non-enterotoxigenic strain G58–1 did not induce clinical illness, and piglets inoculated with this strain were euthanized at 96 h PI since their survival time would have been indefinite. A linear regression between LT secretion at 6 h of culture for these 3 strains and h-to-a-moribund-condition in inoculated gnotobiotic piglets was conducted. The model-adjusted coefficient of determination (R2) was 0.92 (P < 0.0001), indicating that approximately 92% of the variation in the time-to-a-moribund condition could be explained by the LT secretion level of the inoculum strain (Fig. 3). A second linear regression based on LT concentrations at 18 h of culture yielded a model-adjusted R2 of 0.8842 (P < 0.0001). This lower R2 value supported the hypothesis by Lasaro et al. [21] that virulence is more highly correlated with secretion than total production of LT, since a portion of the LT activity in the supernatants from 18 h cultures originated from lysed cells in the stationary-to-death phases.

Bottom Line: Maximum Likelihood phylogenetic trees constructed using T2SS genes gspC, gspD, gspE and homologs showed that strains 2534-86 and 3030-2 clustered together in the same clade with other porcine-origin ETEC strains in the database, UMNK88 and UMN18.Protein modeling of the ATPase gene (gspE) further revealed a direct relationship between the predicted ATP-binding capacities and LT secretion levels as follows: H10407, -8.8 kcal/mol and 199 ng/ml; 3030-2, -8.6 kcal/mol and 133 ng/ml; and 2534-86, -8.5 kcal/mol and 80 ng/ml.This study demonstrated a direct relationship between predicted ATP-binding capacity of GspE and LT secretion, and between the latter and virulence.

View Article: PubMed Central - PubMed

Affiliation: School of Veterinary Medicine and Biomedical Sciences, University of Nebraska-Lincoln, Lincoln, Nebraska, United States of America.

ABSTRACT
Heat-labile enterotoxin (LT) is an important virulence factor secreted by some strains of enterotoxigenic Escherichia coli (ETEC). The prototypic human-origin strain H10407 secretes LT via a type II secretion system (T2SS). We sought to determine the relationship between the capacity to secrete LT and virulence in porcine-origin wild type (WT) ETEC strains. Sixteen WT ETEC strains isolated from cases of severe diarrheal disease were analyzed by GM1ganglioside enzyme-linked immunosorbent assay to measure LT concentrations in culture supernatants. All strains had detectable LT in supernatants by 2 h of culture and 1 strain, which was particularly virulent in gnotobiotic piglets (3030-2), had the highest LT secretion level all porcine-origin WT strains tested (P<0.05). The level of LT secretion (concentration in supernatants at 6-h culture) explained 92% of the variation in time-to-a-moribund-condition (R2 = 0.92, P<0.0001) in gnotobiotic piglets inoculated with either strain 3030-2, or an ETEC strain of lesser virulence (2534-86), or a non-enterotoxigenic WT strain (G58-1). All 16 porcine ETEC strains were positive by PCR analysis for the T2SS genes, gspD and gspK, and bioinformatic analysis of 4 porcine-origin strains for which complete genomic sequences were available revealed a T2SS with a high degree of homology to that of H10407. Maximum Likelihood phylogenetic trees constructed using T2SS genes gspC, gspD, gspE and homologs showed that strains 2534-86 and 3030-2 clustered together in the same clade with other porcine-origin ETEC strains in the database, UMNK88 and UMN18. Protein modeling of the ATPase gene (gspE) further revealed a direct relationship between the predicted ATP-binding capacities and LT secretion levels as follows: H10407, -8.8 kcal/mol and 199 ng/ml; 3030-2, -8.6 kcal/mol and 133 ng/ml; and 2534-86, -8.5 kcal/mol and 80 ng/ml. This study demonstrated a direct relationship between predicted ATP-binding capacity of GspE and LT secretion, and between the latter and virulence.

No MeSH data available.


Related in: MedlinePlus