MIC (Antimicrobial Activity – MIC) Assay

The minimum inhibitory concentration (MIC) is a key microbiological parameter for determining the lowest concentration of a compound capable of visibly inhibiting the growth of a microorganism. It is one of the most reliable indicators for evaluating the antimicrobial efficacy of an extract, functional ingredient, or active molecule intended for animal nutrition.

MIC determination is commonly used in R&D studies, the development of new additives, the selection of alternatives to antibiotics, and the validation of plant or fermentative ingredients with antimicrobial properties.

Importance of dosage in animal nutrition

The MIC has become a strategic tool for animal nutrition manufacturers, in a context of reduced use of antibiotics and strong demand for natural solutions.

It allows, in particular:

• selection of new antimicrobial molecules derived from plants, yeasts, lactic acid bacteria or fungi
• optimization of nutritional additives (essential oils, polyphenolic extracts, antimicrobial peptides)
• comparative evaluation of the effectiveness of ingredients used to modulate the microbiota
• quality control of assets claiming antibacterial activity
• scientific validation during the development of alternatives to antibiotics (AAAs)
• microbiological characterization of raw materials intended for animal feed

The results obtained are crucial for establishing active doses, adjusting formulations, and scientifically documenting a product's performance.

Analytical method

The reference method for determining MIC is microdilution in broth, a standardized technique in microbiology.

The procedure is based on:

The preparation of successive dilutions of the compound to be tested
, inoculation with a standardized microbial suspension
, controlled incubation according to the strain studied,
and visual or instrumental observation of growth.

The MIC corresponds to the lowest concentration in which no visible growth is observed.

Depending on the nature of the ingredient, other parameters may be associated:

kinetic growth (OD)
analyses; determination of the minimum bactericidal concentration (MBC) if necessary

Microorganisms studied

The selection of strains is defined according to demand, and may include:

• pathogenic bacteria of interest in livestock farming (Salmonella, E. coli, Clostridium, Staphylococcus)
• spoilage bacteria
• bacteria of nutritional interest (Lactobacillus, Bifidobacterium)
• yeasts and fungi in certain R&D projects

The tests are carried out under standardized conditions to ensure the reproducibility of the results.

Analyzed matrices

• plant extracts
• Essential oils and aromatic fractions
• fermented ingredients (postbiotics, bacterial metabolites)
• additives for premixes and compound foods
• purified active molecules
• agri-food raw materials

Additional analyses

To interpret or complement the results of the CMI, several analyses from the YesWeLab catalogue are particularly relevant.

Total antioxidant status (TAS) assay.
Antioxidant compounds often exhibit associated antimicrobial activity.

Total polyphenol content assay:
Plant extracts rich in polyphenols are frequently tested by MIC.

Flavonoid assay:
Direct links between flavonoid structure and antimicrobial capacity.

Free amino acid assay
Relevant when bioactive peptides derived from proteins exhibit antimicrobial activity.

Applications in formulation and R&D

• phytogenic additives
• essential oils for poultry and ruminants
• Postbiotics and Fermentation Metabolites
• antimicrobial peptides
• organic acids and buffered mixtures
• technical ingredients for digestive hygiene

Determining the MIC allows for scientific documentation of the effectiveness of an active ingredient, comparison of several plant sources, and definition of functional doses in animal feed.

Why choose YesWeLab?

YesWeLab enables additive manufacturers, R&D laboratories, and nutritionists to quickly access specialized microbiology platforms. Through a network of expert laboratories, we guarantee standardized methods, reliable interpretation, and dedicated scientific support—essential for ensuring the safety of your developments and comparative studies.