Abstract

A ban on the use of antibiotics in livestock was introduced to combat the global antibiotic resistance crisis. This ban has led to an increased prevalence of diseases that have a significant economic impact on the agricultural industry, such as necrotic enteritis (NE) in poultry. As a result, alternative methods are required to prevent these diseases. The main aim of this project was to identify isolates of Bacillus subtilis subsp. subtilis that can be used as probiotics to combat NE in poultry. This study selected B. subtilis subsp. subtilis isolates based on their antagonistic ability against Clostridium perfringens and further assessed their stability in conditions relevant to those of the poultry gastrointestinal (GI) tract, antibiotic sensitivity, and their cell adhesion properties through an aggregation assay. Isolates of interest (BS013 and BS023) showed antagonistic properties against a range of C. perfringens isolates and were also both viable and had antagonistic properties after exposure to pH 2 to pH 9, bile salt concentrations up to 0.9% and temperatures from 30°C to 42°C. The two potential probiotics were deemed susceptible to three antibiotics by European Food Safety Authority (EFSA) guidelines, as well as, providing good auto-aggregation properties, which is thought to be crucial for intestinal cell adhesion. Overall, B. subtilis subsp. subtilis isolates BS013 and BS023 could be promising alternatives to antimicrobial growth promotors (AGPs) to combat NE in poultry, however extensive future work is needed to further assess their effectiveness as probiotics and to ensure safety requirements are met.