OREGANO ESSENTIAL OIL ANTIBACTERIAL EFFICACY AGAINST SALMONELLA SPECIES AFFECTING CATTLE

SUMMARY
A trial was conducted in collaboration with a UKAS accredited microbiology laboratory in the UK, to determine the antibacterial efficacy of oregano essential oil (OEO) against Salmonella dublin and Salmonella typhimurium using the zone of inhibition, disk diffusion technique. The result of this trial supports that OEO has antibacterial efficacy against S. dublin and S. typhimurium and is therefore suitable as part of a cattle biosecurity plan to minimise the risk of contamination caused by these pathogens.

BACKGROUND
S. dublin is the most common Salmonella serotype found in cattle, followed by S. typhimuirium. Whilst antibiotics have been widely used to treat Salmonella spp., this has been shown to create carrier animals or lead to antimicrobial resistance. This trial was conducted as part of Anpario’s 4 R’s approach to antibiotic usage. Orego-Stim (OS) contains 100% natural oregano essential oil (OEO) and has been shown to have antibacterial efficacy against other gram-negative Salmonella spp. implicated in important ruminant diseases and human food safety. TRIAL DESIGN An in vitro trial was conducted in collaboration with a UKAS accredited microbiology laboratory in the UK in 2023-24, to determine the antibacterial efficacy of OEO against S. dublin and S. typhimurium using the zone of inhibition, disk diffusion technique. A bacterial inoculum level of 1 x 107 – 1 x 108 was obtained and streaked over the surface of a dried Mueller Hinton agar plate to ensure an even distribution. Three replicate plates were prepared, where each replicate consisted of using one drop of OEO added per 6mm Whatman filter disc. These were incubated aerobically for 24 hours. Zone of inhibition was characterised as the area without bacterial growth and was measured using digital callipers. A large zone of inhibition would suggest a product is effective at inhibiting bacterial replication in the conditions tested.

Figure 1: Antibacterial efficacy of OEO against S. dublin and S. typhimurium by zone of inhibition. The results of these studies support that OEO has antibacterial efficacy against S. dublin and S. typhimurium (figure 1). Orego-Stim including OEO can therefore be used to help support cattle biosecurity programmes where there is a risk of S. dublin and S. typhimurium contamination.