ISO 15214:1998 PDF

Overview

ISO 15214:1998 - "Microbiology of food and animal feeding stuffs - Horizontal method for the enumeration of mesophilic lactic acid bacteria - Colony-count technique at 30 °C" - is an international standard that defines a horizontal colony‑count method for enumerating viable mesophilic lactic acid bacteria (LAB) in food and feed. The method uses MRS agar (pH 5.7), pour‑plate or surface plating, incubation at 30 °C for 72 hours, and standard dilution techniques to report colony counts per gram or millilitre.

This standard is intended for products for human consumption and animal feedingstuffs, subject to limitations where psychrotrophic or thermophilic LAB require different temperatures or where certain LAB do not grow well on MRS agar.

Key topics and requirements

• Target organisms: Mesophilic lactic acid bacteria (defined as colonies forming at 30 °C on MRS agar pH 5.7).
• Culture medium: MRS agar (de Man, Rogosa and Sharpe) adjusted to pH 5.7 ± 0.1 after sterilization; composition specified in the standard. Option to add sorbic acid when heavy yeast contamination is expected.
• Sample preparation & dilutions: Follow ISO 6887‑1 principles for initial suspension and decimal dilutions; use appropriate diluent (note buffered peptone water may not always resuscitate LAB effectively).
• Plating & incubation: Pour‑plate (or surface plating with anaerobic/microaerobic conditions) of 1 ml inoculum per plate, pour ~15 ml MRS agar at ~47 °C, incubate at 30 °C ± 1 °C for 72 h.
• Colony counting & interpretation: Retain plates with fewer than 300 colonies at two successive dilutions and at least 15 colonies on one dish; apply the weighted-mean equation provided to calculate counts and round to two significant figures.
• Confirmation & reporting: Where non‑LAB growth occurs, simple confirmations (Gram stain, catalase test) may be used and must be reported. Test report must include sample ID, method reference (ISO 15214), any deviations, and results with confidence limits (see ISO 7218).

Applications and who uses it

• Quality control and microbiological enumeration in food microbiology and animal feed testing laboratories.
• Food and feed manufacturers (dairy, fermented foods, processed feeds) for routine monitoring of LAB populations.
• Regulatory and certification bodies that require standardized enumeration methods for compliance or surveillance.
• Research laboratories studying LAB counts in food matrices where a standardized horizontal method is required.

Keywords: ISO 15214:1998, lactic acid bacteria enumeration, MRS agar, colony-count technique, mesophilic LAB, food microbiology, pour-plate method, incubation 30 °C, ISO standard.

Related standards

• ISO 6887‑1 - Preparation of test samples, initial suspension and decimal dilutions.
• ISO 7218 - General rules for microbiological examinations (laboratory practice and reporting).