title: Inactivation of Escherichia coli O157:H7 in simulated human gastric fluid.
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 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 degrees 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 log(10) 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.
authors.affiliation: Eastern Regional Research Center, ARS, USDA, 600 East Mermaid Ln., Wyndmoor, PA 19038, USA. mtamplin@errc.ars.usda.gov
authors.forename: Mark L
authors.initials: ML
authors.lastname: Tamplin
mesh_terms: D000818:Animals; D000863:Antacids / Q000378:metabolism; D002417:Cattle; D015169:Colony Count, Microbial; D003470:Culture Media; D019453:Escherichia coli O157 / Q000254:growth & development*; D005750:Gastric Juice / Q000382:microbiology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008461:Meat Products / Q000382:microbiology; D012760:Shigella / Q000254:growth & development; D012763:Shigella flexneri / Q000254:growth & development; D012965:Sodium Chloride
chemical_list: D000863:Antacids; D003470:Culture Media; D012965:Sodium Chloride