• Antibacterial action of an antimicrobial can be assessed by investigating the zone of inhibition.
  • The antibacterial action of pHorce on 5 different bacteria was assessed and compared to 6 antibiotics.
  • pHorce produced significantly larger zones of inhibition compared to all antibiotics for 4 out of the 5 bacteria, indicating that it is an effective, broad sprectrum, antimicrobial.


  • The antibacterial effect of a product can be easily compared using a zone of inhibition test. This highlights the sensitivity of a known bacteria to multiple products.
  • The larger the zone of inhibition, the more effective the product is against the chosen bacteria.
  • pHorce is a highly concentrated liquid blend of formic and propionic acid formulated on Anpario’s innovative carrier system. The triple action effect of pHorce provides proven anti-bacterial, anti-fungal and anti-viral function.
  • This work is part of Anpario’s 4R’s approach (Review, Reduce and Replace antimicrobials Responsibly) which helps to maintain gut health and support healthier livestock through the use of natural products.

The trial was undertaken by an independent microbiology laboratory in the UK in 2020. A variety of antibiotics and bacterial challenges were selected to account for the most common challenges and associated therapeutic treatment globally. Bacteria were suspended in 20ml of diluent, shaken and the concentration adjusted to contain between 1.5 x 108 – 5.0 x 108 cfu/ml. Plates were prepared in triplicate and incubated at 36ºC ± 1 hour for 24 hours. The zone of inhibition was measured using calipers.

Bacteria selected for use in the trial included:

  • Salmonella typhimurium
  • Escherichia coli (O157)
  • Staphylococcus aureus
  • Staphylococcus uberis
  • Pseudomonas aeruginosa


Antibacterial efficacy of the following treatments against each bacteria were assessed:

  • Lincomycin
  • Amoxicillin
  • Trimethoprim
  • Bacitracin
  • Chloramphenicol
  • Tetracycline
  • pHorce


  • pHorce demonstrated a significantly larger zone of inhibition against Salmonella typhimurium (Figure 1) and E.coli than any of the other treatments tested (Figure 2).
  • When testing efficacy of treatment against Staphylococcus aureus, the antimicrobial activity of pHorce was comparable to Amoxicillin and was significantly more than all the other antibiotics tested (Figure 3).
  • Amoxicillin was most effective against Staphylococcus uberis. However, the antimicrobial efficacy of pHorce was comparable to Lincomycin and Tetracycline and was significantly more than other antibiotic treatments (Figure 4).
  • pHorce produced a significantly larger zone of inhibition compared to all antibiotics tested for efficacy against Pseudomonas aeruginosa (Figure 5).
  • The results of the trial indicated that pHorce was able to produce a larger zone of inhibition than all the antibiotics tested in 4 of the 5 bacterial challenges.

  • Differing letters denote significant differences between treatments (p<0.0001).