Pathogen testing under MOPH No. 416: the method table is your media list

Since early January 2021, the pathogenic-microorganism criteria for foods produced or imported for sale in Thailand have come from Notification of the Ministry of Public Health No. 416 (B.E. 2563). Clause 1 repeals No. 364 (B.E. 2556), dated 25 September 2013, in full. The notification was gazetted on 9 October 2020 and took effect once 90 days had passed. If the criteria table taped up in your QC lab traces back to 364, it has been citing a repealed text for five years.

The notification itself is five clauses. The substance is in three annexes. Annex 1 lists 40 food groups with specific pathogen requirements, plus another 3 that fall under the general ones. Annex 2 sets the tolerated quantity per product-and-pathogen pair. Annex 3 is the one almost nobody opens: the analytical method per pathogen, and the only annex that decides what your lab has to buy.

The method table is the purchase order

Most labs choose in the wrong direction: catalogue first, a familiar brand, then a check that the method roughly fits. Clause 3 makes the Annex 3 methods part of the standard itself, so a medium on your shelf has exactly two possible statuses. Either it is what the named method calls for, or it is a deviation you will be explaining in an audit.

What Annex 3 prescribes, per pathogen:

• Salmonella spp.: ISO 6579-1, except water and ice, which use ISO 19250
• Staphylococcus aureus: US FDA BAM Chapter 12, except water and ice, which use the APHA Standard Methods
• Bacillus cereus: BAM Chapter 14
• Clostridium perfringens: BAM Chapter 16
• Listeria monocytogenes: ISO 11290-1
• Cronobacter spp.: ISO 22964
• Vibrio cholerae and V. parahaemolyticus: ISO 21872-1, with BAM Chapter 9 also accepted for V. parahaemolyticus
• Clostridium botulinum: BAM Chapter 21A

Every line carries the phrase "updated version". The edition that binds you is the current one, not the one in force when the notification was signed in 2020, so your SOPs have to track method revisions.

What the named methods put on your shelf

Salmonella: ISO 6579-1

Pre-enrichment in buffered peptone water, then two selective enrichments run in parallel: RVS broth (or MSRV agar) at 41.5 degrees and MKTTn broth at 37 degrees, 24 hours each. Plating is XLD agar plus one complementary solid medium of the lab's own choosing. That second plate is the detail people miss. XLD alone does not satisfy the method; the standard always requires a complementary medium. For drinking water, ice and natural mineral water, the notification routes you to ISO 19250 instead, against a criterion of not detected in 100 mL.

S. aureus: BAM Chapter 12

Direct plating on Baird-Parker agar, incubated 45 to 48 hours at 35 to 37 degrees. Low-count products use the three-tube MPN in trypticase soy broth with 10% NaCl and 1% sodium pyruvate. Note what is absent: mannitol salt agar appears nowhere in Chapter 12. MSA is a decent screening plate and food labs buy plenty of it, but the count you set against Annex 2 has to come off Baird-Parker. One more thing many labs have not caught: the March 2016 edition widened the incubation temperature from a flat 35 degrees to 35 to 37. That is what "updated version" means in practice.

B. cereus: BAM Chapter 14

MYP (mannitol egg-yolk polymyxin) is the standard plate, and the chapter is blunt about its weakness: little selectivity, so background flora can mask the target. Since the January 2012 update the chapter accepts chromogenic Bacara plates as a substitute, on which colonies grow pink-orange with a precipitation zone. A lab that counts B. cereus routinely in starch or dairy products should stock both.

Listeria: ISO 11290-1

Two-stage enrichment: half-Fraser for 25 hours plus or minus 1, then Fraser for 24 hours plus or minus 2, followed by isolation on the chromogenic agar the standard names, ALOA (agar Listeria according to Ottaviani and Agosti). The 2017 edition widened the scope to Listeria spp. as a genus, not only L. monocytogenes.

Three traps

First, the correction notice. On 27 October 2020 the Royal Gazette published a correction to this notification, fixing the S. aureus entries for several products, including units misprinted as CFU/g where CFU/mL was meant in the beverage and water rows. PDFs downloaded before that date still circulate in procurement inboxes today. If your criteria table came from a blog or an old file, reconcile it against the Thai FDA food-law page, which lists both the notification and the correction.

Second, Clause 4: health supplement products and food additives are outside the scope of 416. Supplement factories still get asked for these tests by trade customers, but their legal criteria sit in the supplement notifications, not here. Do not copy Annex 2 into your own spec.

Third, Annex 3 does not lock you to the listed methods. Its section 2 admits methods from national or international standards bodies, and section 3 admits validated alternatives, with results documented in line with the latest ISO/IEC 17025. In practice that means an in-house lab can run validated rapid kits for process control while an accredited contract lab issues the reference-method results for full compliance. It is the same shape GMP 420 gives annual verification testing, which we covered separately in the factory water-testing guide.

A starting stock for a food QC lab

For the three organisms that appear most often in Annex 2 for general foods (Salmonella, S. aureus, B. cereus), the standing stock is: buffered peptone water, RVS or MSRV, MKTTn, XLD plus one complementary plate, Baird-Parker with egg yolk tellurite supplement, the salt TSB formulation, MYP with polymyxin, petri dishes, stomacher bags and a paddle blender. Everything beyond that should scale with your row in Annex 2, not with the catalogue.

Facts in this article were checked against the texts published by the Thai FDA and the method-issuing bodies on 24 August 2026. Every listed method carries an updated-version condition, so an edition issued after that date governs automatically. Check current status against the Thai FDA food-law page before citing this in procurement or an audit.