Pathogen flora in milk - multi-criteria♦ - 2025

Introduction

The proficiency testings and criteria marked with an ♦ are covered by the « accréditation n° 1-2473, comparaisons interlaboratoires, portée disponible sur www.cofrac.fr »/« n° 1-2473 accreditation, interlaboratory comparisons, scope available on www.cofrac.fr », and detailed flexible scope available there

- We propose tests for the enumeration of Listeria monocytogenes in milk and cheese which must not be mistaken for tests for detection of Listeria.

- The tests for the detection of Salmonella do not concern Salmonella Typhi and Paratyphi.

- The enumeration of sulfito-reducing Clostridium spp., Clostridium perfringens and Bacillus cereus concerns non-spore-forming bacteria. The analysis must be carried out without heat treatment.

In accordance with ISO 15213-1:2023, “ASR bacteria” is used if no confirmation step of characteristic colonies is carried out. If characteristic colonies are confirmed, the “Clostridium spp. sulfito-reducing agents” term is then applied.

- We draw your attention to the fact that we don’t contaminate our samples with collection strains but with strains isolated from dairy food matrices. Therefore, it is possible that some of them present unexpected phenotypic characteristics on some culture media.

Methods / Analytes

- detection of Listeria♦ and Salmonella♦,

- enumeration of coagulase positive Staphylococci♦, Escherichia coli♦, Bacillus cereus♦, Clostridium perfringens♦ and ASR / sulfito-reducing Clostridium spp.♦ 

free choice for methods

Number of samples

→ 5 samples for the detection of:
- Listeria in 25 ml of milk and identification of the species, included Listeria monocytogenes
- Salmonella in 25 ml of milk

→ 5 samples containing between about around:
- 0 and 10 000 coagulase positive staphylococci/ml
- 0 and 100 000 Escherichia coli/ml
- 0 and 1 000 Clostridium perfringens (without thermisation)/ml
- 0 and 1 000 ASR / sulfito- reducing Clostridium spp. (without thermisation)/ml

→ 5 samples containing between around:
- 0 and 30 000 Bacillus cereus (without thermisation)/ml

→ 1 vial of water to control the temperature of the samples at reception

Packaging

- five 60 ml screw-capped vials for the detection of Listeria and Salmonella
- five 30 ml screw-capped vials with airtight seals, for the enumeration of Staphylococci, Escherichia coli, ASR / sulfito-reducing Clostridium spp. and Clostridium perfringens
- five 30 ml screw-capped vials with airtight seals, for the enumeration of Bacillus cereus

Preservation

storage at 3 (±2) °C, with a bacteriostatic mixture preventing any bacterial growth in the milk, but rendered inactive upon dilution.

CAUTION no bacterial growth occurs in the undiluted sample with ready-to-use rehydratable medium (because of the bacteriostatic mixture). It is unnecessary to inoculate this undiluted sample.

Dispatch

in IATA certified secondary packaging (biohazard), in insulated box with ice packs by express carrier (see regulation for shipping times)

Storage in the laboratory

at 3 (±2) °C

Validity of the samples

analyses must be carried out within 3 days after the date of dispatch

Calendar of dispatch :

Subscription at least 10 days before each dispatch

Special conditions :

• For groups from 10 to 24 participating laboratories: 10 % discount,
• For groups from 25 participating laboratories: 15 % discount

Payment conditions :

within 1 month of receiving invoice