Abstract
Shiga toxin-producing Escherichia coli (STEC) are responsible for human infections, ranging from mild watery diarrhea to hemorrhagic colitis (CH) that may be complicated by hemolytic uremic syndrome (HUS). The main STEC virulence factor is Shiga toxin encoded by the stx gene, located in the genome of a bacteriophage integrated into the bacterial chromosome. The serotype O26:H11 is the second HUS-causing serotype worldwide (after O157:H7), and the first found in dairy products such as raw-milk cheeses. A small number of HUS cases identified each year in France are caused by serotype O26:H11. Stx phage induction is known to result in STEC lysis and release of new Stx phages particles. This phenomenon could negatively impact STEC screening in foods based on stx gene detection by PCR. Here, we evaluated the influence of physicochemical parameters related to cheese-making process on the induction rate of Stx phages from STEC O26:H11, including H2O2, NaCl, lactic acid and temperature. In addition, selective agents from the analytical STEC enrichment and detection procedure (XP CEN ISO/TS 13136) were tested, including novobiocin, acrifavin, cefixim-tellurite, and bile salts. An impact of H2O2 and NaCl on Stx phage induction was observed. Production of Stx phages was also observed during a real cheese-making process. By contrast, no significant effect could be demonstrated for the chemical agents of the STEC detection procedure when tested separately, except for acriflavin and novobiocin which reduced Stx1 phage production in some cases. In conclusion, these results suggest that the cheese-making process might trigger the production of Stx phages, potentially interfering with the analysis of STEC in food.
Highlights
Shiga toxin-producing Escherichia coli (STEC) O26:H11 were first identified as causes of hemolytic uremic syndrome (HUS) in 1983 (Karmali et al, 1983; Tarr et al, 2005)
We demonstrated that oxidative stress and, to a lesser extent, salt stress, both occurring during cheese-making processes, have the ability to induce Stx phages in vitro
Production of Stx phages was observed during a real cheese-making process when milk was inoculated by a STEC O26:H11 strain
Summary
Shiga toxin-producing Escherichia coli (STEC) O26:H11 were first identified as causes of hemolytic uremic syndrome (HUS) in 1983 (Karmali et al, 1983; Tarr et al, 2005). They correspond to one of the most commonly isolated non-O157:H7 serotype worldwide, accounting for 12% of all clinical enterohemorrhagic E. coli (EHEC) in Europe in 2012 (Zimmerhackl et al, 2010; EFSA, 2014). Stress and Stx Phages Induction and for 22% of clinical non-O157 EHEC isolates in the United States between 1983 and 2002 (Brooks et al, 2005). We described the induction of Stx phages from STEC O26:H11 by mitomycin C, and showed that Stx phages were more inducible than Stx phages (Bonanno et al, 2016)
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