I read this review article:
Processing environment monitoring in low moisture food production facilities: Are we looking for the right microorganisms? (Open Access)
International Journal of Food Microbiology
Volume 356, 16 October 2021, 109351
In the article:
Microbial tests that are commonly used include aerobic mesophilic counts, Enterobacteriaceae counts or yeast and mould counts (Article 5, EU Regulation 2073/2005).
1.4. PEM in guidelines and legislation
PEM is widely recognized as a requirement in the production of many types of food and is mentioned in numerous publications. For example, in the European Commission Regulation on Microbiological Criteria for Foods (European Commission, 2005), as well as highlighting a range of food safety criteria, it is noted in Article 5 that: “Samples shall be taken from processing areas and equipment used in food production, when such sampling is necessary for ensuring that the criteria are met”. The regulation goes on to specifically identify ready-to-eat (RTE) foods which may pose a Listeria monocytogenes risk, and dried infant formula that may pose a risk from Salmonella spp. and Cronobacter spp., as two product types where PEM is required. This regulation also gives some guidance on the importance of sampling when undertaking PEM and points to ISO 18593 as a standard for the swabbing examination (ISO, 2018).
Thus, I searched Commission Regulation (EC) No 2073/2005 (updated: 2020-03-08)
Article 5
Specific rules for testing and sampling
1. The analytical methods and the sampling plans and methods in Annex I shall be applied as reference methods.
2. Samples shall be taken from processing areas and equipment used in food production, when such sampling is necessary for ensuring that the criteria are met. In that sampling the ISO standard 18593 shall be used as a reference method.
And I checked this standard
ISO 18593:2018
Microbiology of the food chain — Horizontal methods for surface sampling
Abstract
This document specifies horizontal methods for sampling techniques using contact plates, stick swabs, sponges and cloths on surfaces in the food chain environment in order to detect and enumerate culturable microorganisms such as pathogenic or non-pathogenic bacteria or yeasts and moulds.
NOTE The term "environment" means any item in contact with the food product or likely to represent a contamination or recontamination source; for example, material, premises or operators.
This document does not apply to the validation of cleaning and disinfection procedures.
This document does not apply to sampling techniques for primary production samples, which are covered by ISO 13307. Sampling techniques for carcasses are covered by ISO 17604. Sampling techniques for analysis of noroviruses and hepatitis A viruses are covered by ISO 15216-1.
This document does not give advice on sampling frequency, the number of sampling points, or the need to rotate sampling points, as these are chosen on a case-by-case basis.
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I also got this
(Open access)
European survey and evaluation of sampling methods recommended by the standard EN ISO 18593 for the detection of Listeria monocytogenes and Pseudomonas fluorescens on industrial surfaces
