Abstract
Shiga-toxin producing Escherichia coli (STEC) are important foodborne pathogens involved in gastrointestinal diseases. Furthermore, the recurrent use of antibiotics to treat different bacterial infections in animals has increased the spread of antibiotic-resistant bacteria, including E. coli, in foods of animal origin. The use of bacteriophages for the control of these microorganisms is therefore regarded as a valid alternative, especially considering the numerous advantages (high specificity, self-replicating, self-limiting, harmless to humans, animals, and plants). This study aimed to isolate bacteriophages active on STEC strains and to set up a suspension of viral particles that can be potentially used to control STEC food contamination. Thirty-one STEC of different serogroups (O26; O157; O111; O113; O145; O23, O76, O86, O91, O103, O104, O121, O128, and O139) were investigated for their antibiotic resistance profile and sensitivity to phage attack. Ten percent of strains exhibited a high multi-resistance profile, whereas ampicillin was the most effective antibiotic by inhibiting 65% of tested bacteria. On the other side, a total of 20 phages were isolated from feces, sewage, and bedding material of cattle. The viral particles proved not to carry genes codifying Shiga-toxins and intimin. No STEC was resistant to all phages, although some strains revealed weak sensitivity by forming turbid plaques. Three different bacteriophages (forming the “cocktail”) were selected considering their different RAPD (Random Amplification of Polymorphic DNA) profiles and the absence of virulence-encoding genes and antibiotic-resistance genes. The lytic ability against STEC strains was investigated at different multiplicity of infection (MOI = 0.1, 1, and 10). Significant differences (p < 0.05) among mean values of optical density were observed by comparing results of experiments at different MOI and controls. An effective reduction of bacterial population was obtained in 81% of cases, with top performance when the highest MOI was applied. The efficacy of the phage cocktail was tested on fresh cucumbers. Results showed a reduction in pathogenic E. coli by 1.97–2.01 log CFU/g at 25°C and by 1.16–2.01 log CFU/g at 4°C during 24 h, suggesting that the formulated cocktail could have the potential to be used in bio controlling STEC different serogroups.
Highlights
Certain strains of Escherichia coli, a bacterium that is naturally resident in the human gut, can cause gastrointestinal diseases, bloody diarrhea that can develop in complex illnesses as hemorrhagic colitis (HC) and hemolytic-uremic syndrome (HUS) (Kaper et al, 2004)
The last European Union One Health 2018 Zoonoses Report (European Food Safety Authority (EFSA) and ECDC, 2019) indicated Shiga-toxin producing Escherichia coli (STEC) infections in humans as the third most commonly reported zoonosis in the EU with a notification rate increased by 39.0% compared with 2017
The use of bacteriophage for reducing microbial pathogens in food is well established (Moye et al, 2018) and in 2009 the European Food Safety Authority (EFSA) reported that bacteriophages can be very effective in the elimination of pathogens from meat, milk, and dairy products (EFSA, 2009)
Summary
Certain strains of Escherichia coli, a bacterium that is naturally resident in the human gut, can cause gastrointestinal diseases, bloody diarrhea that can develop in complex illnesses as hemorrhagic colitis (HC) and hemolytic-uremic syndrome (HUS) (Kaper et al, 2004). Serotype O157:H7 is still the most common one related to human illness, but non-O157 strains, and in particular O26, O103, and O91, are increasing in importance (Croxen et al, 2013; EFSA and ECDC, 2019) With these data in mind, it is easy to understand the importance to improve techniques for the control of STEC for food safety and consumer protection. The use of bacteriophage for reducing microbial pathogens in food is well established (Moye et al, 2018) and in 2009 the European Food Safety Authority (EFSA) reported that bacteriophages can be very effective in the elimination of pathogens from meat, milk, and dairy products (EFSA, 2009)
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