Microbiological Monitoring – Sources of Contamination

Excerpt from the GMP Compliance Adviser, Chapter 10.E, Microbiological Monitoring

5 min. reading time | by Michael Rieth
Published in LOGFILE 06/2026 

Microbiological monitoring helps identify and control potential sources of microbial contamination in pharmaceutical manufacturing. By monitoring air, surfaces, personnel, and media, companies can detect deviations early and maintain controlled production conditions.

All pharmaceutical dosage forms must be manufactured under controlled microbiological conditions. This requires microbial monitoring. This applies not only to sterile manufacturing, but also to facilities that manufacture non-sterile products.

The aim of monitoring in facilities manufacturing sterile medicines is to detect deviations from the validated state. In facilities manufacturing non-sterile dosage forms, the general hygiene status and the success of disinfection procedures should be assessed. Monitoring should show that the respective process is under control. Environmental conditions are a crucial prerequisite for the production of sterile products, especially in aseptic manufacturing and filling. As part of the monitoring of production rooms for non-sterile products, the effectiveness of operational hygiene control procedures is checked to optimize cleaning and disinfection steps and personal hygiene if necessary.

According to EMA guidelines, monitoring programs should be designed based on a risk assessment (Environmental Monitoring Risk Assessment) as part of the Contamination Control Strategy (CCS). The aim of this assessment is to identify, evaluate, and mitigate/prevent risks associated with microbial contamination in sterile drug manufacturing areas. The risk assessment process typically includes the following:

Identification of critical control points: Determination of the key areas within the manufacturing environment where microbial contamination poses the greatest risk to product quality and patient safety.

Risk assessment: Evaluation of the likelihood and severity of microbial contamination at each CCP, considering factors such as facility design, equipment, personnel activities, and environmental controls.

Risk mitigation strategies: Development and implementation of measures to minimize or eliminate identified risks, such as improving cleanroom design, enhancing cleaning and disinfection procedures, implementing personnel training programs, and optimizing environmental monitoring protocols.

Ongoing monitoring and review: Continued monitoring of the effectiveness of risk mitigation measures through monitoring programs and regular review of the risk assessment to ensure that it remains up to date and relevant.

Monitoring is carried out based on regulatory requirements and internal risk analysis. It is recommended that the monitoring program be set out in the form of a standard operating procedure. This SOP must contain at least the following points:

• Monitoring limit values (levels)
• Methods/devices
• Frequencies
• Sampling points
• Sampling (responsibility)
• Sample transport (responsibility)
• Processing (responsibility)
• Actions in case of deviations (responsibility)
• Documentation

The work instructions should also specify where the documents (raw data, reports, deviation documents, etc.) are to be stored. This is important with regard to audits. It is advantageous to be able to present the requested documents rapidly, as this gives the inspectors/auditors a positive impression of good organization right from the start. Further microbiological monitoring details (e.g. incubation, culture media, etc.) are described in the relevant laboratory SOPs.

Sources of Contamination

Due to the risks of contamination of the drug from the environment described below, monitoring should cover the following areas:

• Air
• Surfaces
• Personnel
• Media (gases, compressed air, lubricants, etc.)

Air

During the manufacturing process, medicinal products come into contact with either ambient air or the air in laminar flow units with appropriate filtration. The GMP guidelines contain detailed requirements for air quality in specific cases. Annex 1 to the EU GMP Guidelines stipulates that for the manufacture of sterile products, the airborne microbial count in grade A and grade B clean areas must be determined during operation. The results must be taken into account when releasing batches.

While air plays a crucial role in sterile production, its importance in the manufacture of non-sterile preparations is often overestimated. Since the pharmacopoeia accepts relatively high microbial counts in the end product, microbial contamination of products from the air is less critical. Nevertheless, air contamination must not be ignored, as it contains microorganisms (airborne microorganisms, mostly bacteria, fungi, and yeasts) that originate from other sources of contamination (surfaces, personnel). Depending on the season, the occurrence of these airborne microorganisms can vary in number and species spectrum.

Surfaces

Surfaces are also important as a possible source of contamination. Objects that come into contact with the product must be regarded as particularly critical for product contamination, as microorganisms can be transferred directly in this case. In general, indirect contamination can occur anywhere via the air. For these reasons, all surfaces must be considered and evaluated in a risk analysis. Critical areas must be sampled more intensively than non-critical areas.

Inadequate room furnishings (leaky ceilings, doors, and windows, poorly equipped airlock and overpressure systems, etc.) can lead to massive microbial infestations, as disinfection measures may not be effective. Attention must therefore be paid to the furnishings of floors and walls. Paintwork and wall and floor coverings are crucial to the success of disinfection measures. The EU GMP Guideline therefore provides detailed information on facility construction.

Personnel

Since people are involved in almost all production steps, special attention must be paid to personnel hygiene. It must be assumed that personnel are one of the main sources of contamination. Humans are carriers of numerous microorganisms, with aerobic and anaerobic bacteria being present in almost equal numbers. Human skin and mucous membranes are colonized by microorganisms and these are released into the environment when people talk, cough, or sneeze. Microorganisms are transferred to the product either directly, e.g. when a technician comes into contact with the medicinal product, or indirectly, when the microorganisms are first released into the air or onto objects and tools and then settle on the medicinal product.

The common ways to reduce microorganisms for materials and surfaces (sterilization, disinfection) are not possible or only possible to a limited extent for personnel. In most cases, one must limit oneself to alcoholic hand disinfection. In addition, the use of appropriate protective clothing has a decisive influence on the release of microorganisms, particles, and human hair.

The EU GMP Guideline therefore contains detailed information on the use of protective clothing for grade A to D cleanroom areas in Annex 1. In addition to donning and wearing the clothing correctly, it is important to change it regularly, as microbes can penetrate the fabric after a certain period of wear. It is particularly important to change gloves regularly to catch even the smallest unnoticed damage. This applies not only to sterile operations; clothing also plays an important role in operations manufacturing non-sterile products as a protective measure against contamination of the product by microbes coming from personnel. The table below shows a proposal for clothing regulations in accordance with USP 42 Section <1115> from 2019.

Routine monitoring must be carried out for personnel involved in the manufacture of sterile preparations. Behaviour in the clean room must be taught and demonstrated by training. Regular hygiene training is required for personnel involved in the manufacture of non-sterile preparations.

Do you have any questions or suggestions? Please contact us at: redaktion@gmp-verlag.de