Submitted to: Infection and Immunity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2004
Publication Date: 1/1/2005
Citation: Tamplin, M.L. 2005. Inactivation of Escherichia coli 0157:H7 in simulated human gastric fluid. Infection and Immunity. Vol 71. No.1 pg.320-325.
Interpretive Summary: Escherichia coli O157:H7 is known to contaminate raw ground beef and occasionally cause serious human foodborne illness. The low pH of the stomach is an early defense against foodborne infections. Numerous reports have described acid resistance of E. coli O157:H7 in a variety of foods and synthetic media, however few studies have examined the survival of E. coli O157:H7 in ground beef exposed to stomach gastric fluid, including variations among strains, the influence of different amounts of ground beef, and the effect of antacid. To define the survival of E. coli O157:H7 in stomach gastric fluid, multiple E. coli O157:H7 strains were suspended separately or as a mixture in saline, cooked ground beef [CGB], or cooked ground beef containing a commercial antacid product [CGB+A] and incubated with various proportions of simulated human gastric fluid (SGF). The highest rate of inactivation was observed in saline, followed by CGB then CGB+A. In contrast, Shigella spp. were killed 7 to 17 times faster than E. coli O157:H7 strains. The survival rate of E. coli O157:H7 increased as the amount of antacid increased. A similar trend was observed for acidity, indicating that acid is a primary factor controlling E. coli O157:H7 survival. This information is relevant to the development of dose-response models in risk assessment, especially for those that have used Shigella dose-response data to substitute for E. coli O157:H7. We believe that these experiments provide more information about the response of E. coli O157:H7 strains to conditions that may be present in the human stomach and which directly affect the numbers of pathogenic E. coli O157:H7 that gain access to sites of infection.
Technical Abstract: Human disease caused by Escherichia coli O157:H7 is a function of the number of cells that are present at potential sites of infection. Such infectious doses are a result, in part, of the quantity of cells that are ingested and that survive human host defenses, such as the low pH environment of the stomach. To more fully understand the kinetics of E. coli O157:H7 survival in stomach gastric fluid, individual E. coli O157:H7 strains were suspended in various media (saline, cooked ground beef [CGB], and cooked ground beef containing a commercial antacid product [CGB+A], mixed at various proportions with simulated human gastric fluid (SGF), and then incubated at 37°C for up to 4 h. The highest inactivation rate for nine E. coli O157:H7 strains was observed in saline. Specifically, the average survival rates in 100:1 and 10:1 proportions of SGF-saline were -1.344 ± 0.564 and-0.997 ± 0.388, respectively. In contrast, the average inactivation rate for ten E. coli O157:H7 strains suspended in 10:1 SGF-CGB was -0.081 ± 0.068, a rate that was 12-fold lower than that observed for SGF-saline. In comparison, the average inactivation rate for S. flexneri 5348 in 100:1 and 10:1 SGF:saline was -8.784 and -17.310, respectively. These inactivate rates were 7- to 17-fold higher than for E. coli O157:H7 strains in SGF-saline, and 4-fold higher than that for E. coli O157:H7 strains in SGF-CGB. The survival rate of E. coli O157:H7 GFP80EC increased as the dose of antacid increased. A similar trend was observed for the matrix pH, indicating that pH is a primary factor affecting E. coli O157:H7 survival in SGF-CGB+A. These results can be used in risk assessment to define dose-response relationships for E. coli O157:H7, and to evaluate potential surrogate organisms.