Influence of Stress Factors Related to Cheese-Making Process and to STEC Detection Procedure on the Induction of Stx Phages from STEC O26:H11

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.

Robustness and efficacy of an inhibitory consortium against E. coli O26:H11 in raw milk cheeses

“…It is difficult to have a general overview of STEC contamination in cheese because measurement methods have varied from one country to another. Worldwide, serotype O26:H11 is second only to E. coli O157:H7 for causing HUS (Hemolytic Uremic Syndrome), and is the one most often found in dairy products such as raw-milk cheeses (Bonanno, Delubac, Michel, & Auvray, 2017). Miszczycha et al (2014) showed that E. coli O26:H11 grew better and was more persistent than E. coli O157:H7 in various experimentally contaminated raw-milk cheeses.…”

Microbiological quality of raw drinking milk and unpasteurised dairy products: results from England 2013–2019

“…While the most likely reason for non-isolation is the background microbiota, this may also be as a result of free stx -containing phage. Recent studies suggest that the cheesemaking process triggers the production of stx containing prophages, potentially interfering with the analysis of STEC in the finished products [33]. These studies demonstrated that oxidative (aeration and exposure to oxygen) and salt stress, which are both likely to occur during cheesemaking, had the ability to induce stx phages in vitro .…”

Hemolytic uremic syndrome following complicated appendicitis in a child: what is the missing link?

“…One study showed that an increase in temperature can also induce phages when associated with other inducers. 17 Antibiotic treatment of STEC is still a matter of debate, although azithromycin appears to be the most effective agent. 18 Azithromycin is thought to be able to inhibit Stx-stimulated cytokine production by human peripheral blood mononuclear cells and monocytes.…”