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Applied and Environmental Microbiology, January 2005, p. 320-325, Vol. 71, No. 1
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.1.320-325.2005

Inactivation of Escherichia coli O157:H7 in Simulated Human Gastric Fluid

Mark L. Tamplin^*

Eastern Regional Research Center, Microbial Food Safety Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Wyndmoor, Pennsylvania

Received 17 May 2004/ Accepted 30 August 2004

Human disease caused by Escherichia coli O157:H7 is a function of the number of cells that are present at potential sites of infection and host susceptibility. 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 gastric fluid, individual E. coli O157:H7 strains were suspended in various media (i.e., saline, cooked ground beef [CGB], and CGB 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 among 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 log₁₀ CFU/h, respectively. In contrast, the average inactivation rate for 10 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 Shigella flexneri strain 5348 in 100:1 and 10:1 SGF-saline was –8.784 and –17.310, respectively. These latter inactivation rates were 7- to 17-fold higher than those for E. coli O157:H7 strains in SGF-saline and were 4-fold higher than those for E. coli O157:H7 strains in SGF-CGB. The survival rate of E. coli O157:H7 strain GFP80EC increased as the dose of antacid increased from one-half to twice the prescribed dose. A similar trend was observed for the matrix pH over the range of pH 1.6 to 5.7, 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.

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* Mailing address: Eastern Regional Research Center, ARS, USDA, 600 East Mermaid Ln., Wyndmoor, PA 19038. Phone: (215) 836-3794. Fax: (215) 233-6581. E-mail: mtamplin{at}errc.ars.usda.gov.

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Applied and Environmental Microbiology, January 2005, p. 320-325, Vol. 71, No. 1
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.1.320-325.2005

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