title: Effect of preservatives on Shiga toxigenic phages and Shiga toxin of Escherichia coli O157:H7.
abstract: Toxin synthesis by Shiga toxin-producing Escherichia coli (STEC) appears to be coregulated through the induction of the integrated bacteriophages that encode the toxin genes. These phages might be the principal means for the dissemination and release of Shiga toxins. We  evaluated the effect of three common food preservatives, potassium sorbate, sodium benzoate, and sodium propionate, on the propagation of the phages and Shiga toxins. We tested each preservative at four concentrations, 1, 1.25, 2.5, and 5 mg/ml, both on free phages and on lysogenic phages  in bacteria. We also evaluated the expression of a lambdoid phage, which was exposed to increasing concentrations of preservatives, by measuring β-galactosidase activity from SPC105, a transductant strain. Furthermore, we tested the effect of the preservatives on cytotoxigenic activity  of Shiga toxin on Vero cells. We detected an increase of the inhibitory effect of the phage lytic activity, both in lysogenic and free phages, as the preservative concentration increased. However, the inhibition was higher on the lysogenic phages release than on free phages. Sodium benzoate  and potassium sorbate were about equal at inhibiting phages; they were more effective than sodium propionate. A significant decrease of lacZ expression, encoded in a lambda phage, was observed. We also found a reduction in Shiga toxin titer caused by exposure of E. coli O157:H7  to 5 mg/ml sodium benzoate or potassium sorbate. These results imply that these three preservatives, used to inhibit microbial spoilage of foods, also act to inhibit lytic activity and dispersion of a phage carrying the gene encoding powerful Shiga cytotoxins. Also notable was the inactivation  of Shiga toxin activity, although this effect was detected using concentrations of preservatives greater than those allowed by the Argentine Food Code.
authors.affiliation: Área Bacteriología, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531 S2002LRK, Rosario, Santa Fe, Argentina. tomassubils@gmail.com.ar
authors.forename: Tomás
authors.initials: T
authors.lastname: Subils
authors.forename: Virginia
authors.initials: V
authors.lastname: Aquili
authors.forename: Guillermo
authors.initials: G
authors.lastname: Ebner
authors.forename: Claudia
authors.initials: C
authors.lastname: Balagué
mesh_terms: D000818:Animals; D010582:Bacteriophage lambda / Q000187:drug effects; D001435:Bacteriophages / Q000187:drug effects*; D002522:Chlorocebus aethiops; D004305:Dose-Response Relationship, Drug; D005520:Food Preservatives / Q000494:pharmacology*; D008242:Lysogeny; D011422:Propionates / Q000494:pharmacology; D022603:Shiga Toxins / Q000096:biosynthesis*; D054323:Shiga-Toxigenic Escherichia coli / Q000187:drug effects* / Q000821:virology*; D020160:Sodium Benzoate / Q000494:pharmacology; D013011:Sorbic Acid / Q000494:pharmacology; D014709:Vero Cells
chemical_list: D005520:Food Preservatives; D011422:Propionates; D022603:Shiga Toxins; C514135:sodium propionate; D020160:Sodium Benzoate; D013011:Sorbic Acid