Equipping a food microbiology lab for MOPH No. 416: what the methods themselves require

In the method table of MOPH No. 416 we worked backwards from Annex 3 to a culture-media list. This article does the same job for the other half of the lab, the equipment. Every method Annex 3 cites has its own Equipment and materials section: incubator temperatures, petri dish sizes, water bath tolerances, the colony range a plate may be counted in. Put those sections in the order the work actually happens and the purchase list writes itself, with a citation on every line.

The numbers below come from the current edition of each method: FDA BAM Chapter 1 (April 2022), Chapter 3 (January 2026), Chapter 4 (October 2020), Chapter 12 (March 2016), Chapter 14 (October 2020), and ISO 6579-1 and ISO 11290-1 as Annex 3 names them. Annex 3 marks every method as updated version, so the binding edition is the latest one, not the one on the bench when the lab was set up.

Start with the sample: weigh, dilute, homogenize

BAM Chapter 1 states the enumeration preparation plainly: a 50 g analytical unit, 450 ml of Butterfield's phosphate-buffered dilution water, blended for 2 minutes, which gives the 10 to the minus 1 dilution, and further dilutions made promptly. Detection of pathogens such as Salmonella uses 25 g analytical units, which the same chapter allows to be combined into 375 g composites under its sampling plans.

This stage therefore needs a balance for the analytical units, a homogenizer with sterile containers, dilution bottles holding 90 plus or minus 1 ml as Chapter 3 specifies, and pipets of 1, 5 and 10 ml graduated in 0.1 ml units with a pipet aid or pipettors, because Chapter 3 rules out mouth pipetting. BAM writes the step for a blender; in practice, labs working to ISO methods mostly use a paddle homogenizer (stomacher) with sterile bags, which removes the washing and sterilizing of blender jars between samples.

Petri dishes: the sizes the methods ask for

There is no single petri dish. Chapter 3 specifies glass or plastic dishes of at least 15 x 90 mm. Chapter 14, for B. cereus, specifies sterile 15 x 100 mm dishes. The membrane filtration method in Chapter 4 uses sterile plastic 50 x 12 mm dishes with tight-fitting lids, paired with 47 mm membrane filters of 0.45 micrometre pore size. A lab that runs both aerobic plate counts and B. cereus keeps two sizes on the shelf.

Agar volumes carry numbers too. Chapter 3 pours 12 to 15 ml of plate count agar, tempered to 45 plus or minus 1 degrees, into each dish within 15 minutes of the original dilution; plates are not stacked while pouring or while the agar sets, and are inverted for incubation. For pre-poured plates the same chapter suggests about 15 ml per 100 mm dish and 50 ml per 150 mm dish. For yeasts and molds, the M124 formulation specifies 20 to 25 ml in 15 x 100 mm dishes.

Sterile plastic dishes are single-use; glass dishes are washed and autoclaved every cycle. The choice is about throughput and autoclave capacity, not right and wrong. When ordering petri dishes and microbiology consumables, state the size, the sterility and the count per pack in the quotation request; those three move the price per dish more than the brand does.

Incubators: every temperature, at the same time

Incubation is where new labs under-estimate most, because each method incubates at its own temperature and several run at once. What the texts set:

• Aerobic plate count (BAM Chapter 3): 35 plus or minus 1 degrees for 48 plus or minus 2 hours; milk at 32 plus or minus 1 degrees.
• S. aureus on Baird-Parker (BAM Chapter 12): 35 to 37 degrees for 45 to 48 hours, plus a drying cabinet or incubator to dry the agar surface before spreading.
• B. cereus (BAM Chapter 14): incubators at 30 plus or minus 2 and 35 plus or minus 2 degrees; isolation plates 18 to 24 hours at 30 degrees.
• Coliforms and E. coli (BAM Chapter 4): LST enrichment at 35 plus or minus 0.5 degrees, as revised in October 2020.
• Salmonella (ISO 6579-1): selective enrichment in RVS at 41.5 degrees alongside MKTTn at 37 degrees, then isolation at 37 degrees.
• Listeria (ISO 11290-1): half-Fraser at 30 degrees, then Fraser and the isolation plates at 37 degrees.

A lab covering the general criteria of Annex 2 therefore needs at least three set points running at once: 30, 35 to 37 and 41.5 degrees. One incubator cannot be switched between them, because every method incubates overnight and the days overlap. When specifying incubators, start from plates per day times days of incubation, then choose the size. A hot-air oven is not an incubator; its range and uniformity are designed for a different job, so do not substitute one to save a cabinet.

Water baths: the tightest specification on the list

Water baths do two jobs. The first is tempering agar before pouring: Chapter 3 specifies 45 plus or minus 1 degrees, Chapter 14 accepts 45 plus or minus 2 and adds a 100 plus or minus 2 degree bath for melting agar in flasks. The second is far tighter: confirming E. coli in EC tubes under Chapter 4 requires a covered, circulating water bath held at 44.5 plus or minus 0.2 degrees (changed from 45.5 in July 2017), read at 24 plus or minus 2 hours and again at 48 plus or minus 2 hours. An ordinary bath that drifts a degree does not meet it. If your food group's criteria include E. coli or coliforms, put plus or minus 0.2 degrees in the quotation request from the start.

Counting colonies

Chapter 3 specifies a dark-field or Quebec colony counter, or equivalent, with a light source and grid plate, plus a tally register. The countable range is 15 to 300 colonies per plate, which the March 2025 revision changed from 25 to 250. For S. aureus on Baird-Parker, Chapter 12 selects plates with 20 to 200 colonies. Spread plating in Chapter 14 uses glass spreading rods of 3 to 4 mm diameter with a 45 to 55 mm spreading area, spreading 0.1 ml per plate.

Sterilization, safety and waste

Media prepared in-house, such as plate count agar to formulation M124, are autoclaved for 15 minutes at 121 degrees, so the lab needs an autoclave that runs a 121 degree cycle for both media flasks and culture waste, with clean and waste cycles kept apart. The texts then list large and small Bunsen burners, nichrome or platinum wire loops and culture tube racks. A biosafety cabinet is not in BAM's equipment sections, but enriching pathogens is work for which a lab should assess its risk and arrange an aseptic working area suited to the organisms it tests for.

Storing samples and media

Chapter 3 specifies a refrigerator for samples at 0 to 5 degrees (milk 0 to 4.4 degrees) and a freezer to keep frozen samples frozen. Chapter 1 adds that perishable samples are refrigerated on receipt and frozen samples must not thaw in transit. The lab refrigerator therefore needs a thermometer that can be read and logged, and it is not the one that holds lunch. Prepared media and dehydrated powders are stored as each manufacturer's label states.

The starting list for a food microbiology lab

Everything above on one list, with the method each line comes from:

• A balance for 25 g and 50 g analytical units (BAM Chapter 1)
• A homogenizer with sterile bags or jars, and 90 ml dilution bottles (BAM Chapters 1 and 3)
• Pipets of 1, 5 and 10 ml graduated in 0.1 ml with a pipet aid, or micropipettes (BAM Chapter 3)
• Sterile petri dishes 15 x 90 mm and 15 x 100 mm, and 50 x 12 mm for membrane filtration (BAM Chapters 3, 4 and 14)
• Incubators covering 30, 35 to 37 and 41.5 degrees simultaneously, and a cabinet for drying agar surfaces (BAM Chapters 3, 12 and 14; ISO 6579-1; ISO 11290-1)
• A 45 plus or minus 1 degree bath for agar, and a covered circulating bath at 44.5 plus or minus 0.2 degrees if E. coli is tested (BAM Chapters 3 and 4)
• A colony counter with grid plate, a tally register and glass spreading rods (BAM Chapters 3 and 14)
• An autoclave for 121 degree, 15 minute cycles, Bunsen burners, wire loops and tube racks (BAM M124 and Chapter 14)
• A 0 to 5 degree refrigerator and a freezer for samples, with a logging thermometer (BAM Chapters 1 and 3)
• Culture media per the list in the method-table article for MOPH No. 416

When requesting a quotation, state

Samples and plates per day, every incubation temperature the lab must hold at once, the water bath tolerance you need (plus or minus 1 or plus or minus 0.2 degrees), autoclave chamber volume per cycle, dish sizes and counts per pack, and the organisms you test for, because the organism list sets both the media and the safety level of the working area. With that set, the first quotation can already name models that fit the methods. Send a quotation request with this list.

Which cabinet protects the worker, what cycles the autoclave needs and what labour law calls it, and the WHO and ISO 7218 requirements for the room itself are in a separate article: the room around the bench

The facts in this article were checked against the current FDA BAM editions and the Thai FDA food-law page on 21 September 2026. Every method in Annex 3 carries the updated version condition, so an edition issued after that date applies automatically; confirm the latest edition before using these numbers in a purchasing specification or an audit file.