Abstract
Induction and propagation of bacteriophages along the food production chain can represent a significant risk when bacteriophages carry genes for potent toxins. The aim of this study was to evaluate the effect of different compounds used in the food industry on the growth of Shiga toxin-producing Escherichia coli (STEC) and the production of stx-phage particles and Shiga toxin. We tested the in vitro effect of lactic acid, acetic acid, citric acid, disodium phosphate, and sodium citrate on STEC growth. A bacteriostatic effect was observed in most of treated cultures. The exceptions were those treated with sodium citrate and disodium phosphate in which similar growth curves to the untreated control were observed, but with reduced OD600 values. Evaluation of phage production by plaque-based assays showed that cultures treated with sodium citrate and disodium phosphate released phages in similar o lower levels than untreated cultures. However, semi-quantification of Stx revealed higher levels of extracellular Stx in STEC cultures treated with 2.5% sodium citrate than in untreated cultures. Our results reinforce the importance to evaluate if additives and other treatments used to decrease bacterial contamination in food induce stx-phage and Stx production.
Highlights
Shiga toxin-producing Escherichia coli (STEC) are important pathogens that can cause human diseases, like diarrhoea, haemorrhagic colitis, and haemolytic uraemic syndrome (HUS) (Karmali et al, 1985)
The following compounds were prepared in stock solutions and used at indicated final concentrations: lactic acid (0.5 and 2.5% v/v), acetic acid (2.5% v/v), citric acid (0.5 and 2.5% w/v), disodium phosphate (0.1, 0.5, and 1% w/v), and sodium citrate (0.5, 1.0, and 2.5% w/v)
The new cultures were incubated at 37◦C and 120 rpm ∼45 min. up to an optical density at 600 nm (OD600) ≈ 0.2−0.3 when each flask was added with the respective additive, or water, or mitomycin C, reaching a final culture volume of 15.5 ml
Summary
Shiga toxin-producing Escherichia coli (STEC) are important pathogens that can cause human diseases, like diarrhoea, haemorrhagic colitis, and haemolytic uraemic syndrome (HUS) (Karmali et al, 1985). STEC strains are characterized by their capacity to produce Shiga toxins, which are encoded by bacteriophages, usually named stx-phages. These phages influence the pathogenicity of STEC strains, since the expression of these toxins is upregulated when the lytic cycle of these phages is induced. They play a role in the spread of stx among E. coli as well as to other bacteria (Schmidt et al, 1999; Muniesa et al, 2004; Probert et al, 2014). Some antibiotics have been reported to increase phage induction
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