ISO 10932:2010

Overview

ISO 10932:2010 (IDF 223:2010) defines a standardized method for determining the minimal inhibitory concentration (MIC) of antibiotics for bifidobacteria and non-enterococcal lactic acid bacteria (LAB) isolated from milk and milk products. The standard recommends the broth microdilution method as the reference quantitative technique: the MIC is the lowest antibiotic concentration that prevents visible growth under defined in vitro conditions. The document includes procedural steps, media formulations, quality control and reporting requirements relevant to dairy microbiology and probiotic testing.

Key Topics

• Scope and principle
  • Quantitative MIC determination for bifidobacteria and non‑enterococcal LAB using broth microdilution.
  • Definition of MIC (expressed in µg/ml) and the rationale for standardization.
• Culture media and reagents
  • Specification and preparation guidance for recommended media such as MRS agar, MRS-Cys, and M17‑sucrose to avoid media–antibiotic antagonism.
  • Use of analytical-grade reagents, sterile water and pre-reduced media where required.
• Procedure and test setup
  • Colony selection and suspension, propagation, dilution, and inoculation of microdilution plates with two‑fold antibiotic dilution series.
  • Growth conditions and incubation parameters, preparation of microdilution plates (including hand-made options), and criteria for visible growth assessment.
• Quality control and performance
  • Inclusion of control strains, interlaboratory precision (repeatability and reproducibility) data, and validation of media performance.
• Results and reporting
  • How to express MIC values, document test conditions, and report results for regulatory or product‑development use.
• Safety note
  • Warnings on hazards associated with handling antibiotics (e.g., kanamycin, chloramphenicol) and recommended precautions.

Applications

ISO 10932:2010 is directly applicable to:

• Dairy microbiology laboratories testing milk, fermented products and probiotic cultures for antibiotic susceptibility.
• Probiotic and starter-culture manufacturers evaluating strain safety and antibiotic resistance profiles.
• Regulatory agencies and accreditation bodies assessing compliance and harmonizing susceptibility testing methods.
• Research groups studying antimicrobial resistance in LAB from dairy ecosystems.

Benefits include reproducible, comparable MIC data for risk assessment, product development, and surveillance of antibiotic resistance in dairy-associated microorganisms.

Related standards

• ISO 6887-5 - sample preparation for milk and milk products
• ISO 7218 - general microbiological examination requirements
• ISO/TS 11133-1 and -2 - preparation and performance testing of culture media
• ISO 20776-1 - terminology and definitions relating to MIC

Keywords: ISO 10932:2010, MIC determination, broth microdilution, bifidobacteria, lactic acid bacteria, LAB, milk and milk products, MRS agar, antibiotic susceptibility.