🦠 Surface sampling in food establishments — contact plates, swabs, sponges and wipes

Microbiology PN-EN ISO 18593

Overview

Determining the presence or the number of micro-organisms on the surfaces of tools, work stations and equipment in the environment of the food chain makes it possible to assess the level of contamination of the surroundings of production. ISO 18593:2018 (the second edition, replacing ISO 18593:2004; recommendations as to the place, the surface and the time of sampling and examples of neutralisers in annex A were added) specifies horizontal methods of sampling with contact plates, swabs, sponges and wipes from surfaces in the environment of the food chain for the detection and the enumeration of culturable micro-organisms — pathogenic and non-pathogenic bacteria and yeasts and moulds; the "environment" covers everything that is in contact with the product or that may be a source of contamination (material, rooms, operators). The standard does not cover the validation of cleaning and disinfection procedures, sampling from primary production (ISO 13307), sampling of carcases (ISO 17604) or sampling for the analysis of noroviruses and HAV (ISO 15216-1); nor does it lay down the frequency, the number or the rotation of the sampling points. Regulation (EC) No 2073/2005 (article 5(2)) requires the standard ISO 18593 to be used as the reference method when sampling from production areas and equipment, and obliges producers of ready-to-eat food to take environmental samples for the presence of Listeria monocytogenes.

Method principle

Sampling programmes serve to assess the contamination of surfaces so that corrective actions preventing the contamination of food can be implemented; ineffective programmes or techniques may fail to detect the micro-organisms that are present. The determination consists of the taking of a sample from the surface and of the analysis according to the standards for the given micro-organism. The techniques: contact plates (plastic plates of various diameters or other containers allowing contact with the surface; the medium has to form a convex meniscus, is chosen according to the ISO standard for the micro-organism sought and contains a neutraliser where necessary; alternative media require validation in accordance with ISO 16140-2) and dipslides — flat surfaces only; swabs (a stick with cotton or with a synthetic material — alginate, rayon — in a tube or an envelope, with documented absence of inhibitory substances; residues of cotton may contaminate the surfaces) — all kinds of surfaces; sterile wipes and sponges (with or without a holder, free from inhibitory substances) — large surfaces. The diluent: sterile buffered peptone water, peptone salt solution (ISO 6887-1), a 1 g/l peptone solution or quarter-strength Ringer's solution (ISO 6887-5), with neutralisers where residues of disinfectants are expected; a neutraliser is not added when no residues are expected, because it may harm the cells (especially stressed ones); there is no universal neutraliser — those of EN 1276, EN 1650, EN 13697, EN 13704 and of annex A are recommended. The places, the surfaces, the time and the technique of sampling are chosen on the basis of risk, so as to maximise the chance of detecting contaminated surfaces during production; micro-organisms occur on visually clean surfaces, but most often in wet and soiled places that are difficult to reach (openings, crevices, porous, rusting and hollow materials) — sometimes the equipment has to be dismantled; the places are chosen on the basis of historical data and of a step-by-step analysis of the process, and the procedure is kept constant so that trends can be followed.

Applications

• Monitoring of the production environment (Listeria monocytogenes, Salmonella, Enterobacteriaceae, total viable count) in establishments producing ready-to-eat food — an obligation under Regulation 2073/2005
• Verification of the effectiveness of the cleaning and disinfection of lines (contact plates, dipslides) — apart from the validation of the procedures
• Searching for niches and harbourage sites of pathogens (sponges, wipes on large surfaces, swabs in crevices)
• Control of the hygiene of the hands and the clothing of the operators and of the packaging
• Following the trends of contamination (a constant procedure and constant points)

Key parameters

Standard

Standard number

PN-EN ISO 18593:2018-08 (ISO 18593:2018)

Title (PL)

Mikrobiologia łańcucha żywnościowego — Horyzontalne metody pobierania próbek z powierzchni

Title (EN)

Microbiology of the food chain — Horizontal methods for surface sampling

Step-by-step procedure

1. Sampling plan

   Choose the places, the surfaces, the time and the technique according to risk-based principles (a greater probability of detection during production), historical data and a step-by-step analysis of the process; keep the procedure constant for a given routine so that trends can be followed. The standard does not impose either the frequency or the number of points.

2. Choice of the technique and of the diluent

   Flat surfaces — contact plates or dipslides; all surfaces — swabs; large surfaces — sterile wipes or sponges. The diluent in accordance with ISO 6887-1/-5; add a neutraliser only where residues of disinfectants are expected.

3. Sampling

   Take the sample from the delimited area (a template) — press the contact plate onto it or wipe the surface with a moistened swab, sponge or wipe; in places that are difficult to reach (openings, crevices, porous, rusting and hollow materials) dismantle the parts where necessary.

4. Transport

   Transport the samples to the laboratory in an insulated container with cooling packs; for a longer transport use a validated transport diluent.

5. Preparation and analysis

   Mix the swabs, the sponges and the wipes (vortex) or homogenise them in a peristaltic homogeniser in the diluent; incubate the contact plates directly. Analyse them according to the standards for the given micro-organism (e.g. ISO 11290-1/-2 for Listeria, ISO 6579-1 for Salmonella, ISO 21528-2 for Enterobacteriaceae).

6. Result

   Express it as presence/absence or as a number per cm² or per sampling device (an area that is not defined numerically, e.g. a tap, a door handle); interpret it in the context of the trends and of the corrective actions.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Surfaces in establishments may be contaminated with pathogens (Listeria, Salmonella) — gloves, disinfection of the hands, transport of the samples as potentially infectious material
• Dismantling of equipment for sampling — switching off and securing the machines (LOTO)
• Residues of disinfectants on the surfaces — protection of the skin and the eyes

Frequently asked questions