IN THE LAB: Air Sampling
The BioCapt Impactor of the Pall-Ascotec Microbiological Air Monitoring System. The Ascotec brand is owned by Biotrace International Plc.
Do You Know What's in the Air?
Monitoring Airborne Biocontamination in Controlled Environments
In the wake of the recent and much-publicized case of flu vaccine contamination and with the pharmaceutical and biotechnology industries embracing the FDA's process analytical technology (PAT) for microbiology methods, the need for more efficient and reliable microbiological air monitoring systems is even more apparent and is gaining great regulatory support.
Under PAT, the FDA is encouraging pharmaceutical companies to utilize innovative analytical technologies and switch from reliance on final product microbiological quality control toward in-process control at key points in the manufacturing process. The ability to monitor quality and identify contamination events during production enables companies to take appropriate actions quickly and avoid unnecessary economic losses. Moreover, reliable and efficient measurement of microbial air quality in clean-rooms and controlled areas for the life science industry is an important component of any environmental monitoring program. However, due to the variety of automated air samplers currently available in the market, guidance is needed for the selection of air samplers as well as for the methods used to measure their effectiveness.
Most Recent Air Sampling Standards
The latest international standard, ISO 14698-1:2003, "Cleanrooms and associated controlled environments-Biocontamination control," including Annexes A and B, establishes the principles and basic methodology for assessing and controlling biocontamination when cleanroom technology is required. Further, it provides techniques for the detection and monitoring of airborne biocontamination as well as the evaluation and qualification of the efficiency of air samplers. ISO 14698-2, "Evaluation and interpretation of biocontamination data," presents a framework for the evaluation of microbiological data and the estimation of results obtained from particle samples taken in risk zones using the principles and methods given in the first part of this standard.
It is also important to understand that within the content of the biocontamination standard, there is reference to risk assessment. This section states that a formal risk analysis procedure should be implemented to evaluate the area at risk and identify appropriate mechanisms of control as well as establish initial control levels. Thus, a formal system of biocontamination control will evaluate and manage factors that can adversely affect the quality of a process or product. A few examples of a formalized system to accomplish this are the HACCP, Fault Tree Analysis (FTA), Failure Mode and Effect Analysis (FMEA). This is critical information that needs to be addressed when evaluating the appropriate air sampling system.
The next question is whether to implement an active or passive air monitoring system. Passive microbial sampling devices such as settle plates are used to measure the number of microorganisms settling from the air onto a surface area over a period of time. These plates are placed in positions of interest around the cleanroom. They are then collected after several hours, incubated and the resulting colonies are then counted. Annex A.3.3 position on the use of settle plates is they do not measure the total number of viable particles in the air but rather they measure the rate as to the number of particles that settle on surfaces. Further, the standard recommends the use of active air sampling devices in risk zones as essential for the measurement of microbiological quality of air.
Making a Selection
According to Annex A.3.2, there are several important factors to consider when choosing an air sampler: The effective sampling rate of the instrument, duration of sample acquisition and physical attributes of sampling device, all of which have the ability to strongly influence the viability of the microorganisms that are collected. Since there are a number and diversity of microbial air sampling systems available on the market today, ISO 14698-1 recommends the selection for a particular environmental monitoring program should consider, as a minimum, type and size of viable particles to be sampled, sensitivity of the viable particles to the sampling procedure, expected concentration of viable particles, capability to detect high or low levels of biocontamination, appropriate culture media, time and duration of sampling, ambient conditions in the environment being sampled and disturbance of unidirectional airflow by the sampling apparatus.
In addition, air sampler features under consideration must have appropriate suction flow rate for low levels of viable airborne particles, appropriate impact and airflow velocity, collection accuracy and efficiency, ease of handling and operation and simplicity of cleaning and disinfection or sterilization. Furthermore, evaluation of possible intrinsic addition of viable particles to the biocontamination should be measured and most notably the exhaust air from the sampling apparatus should not contaminate the environment being sampled or be re-aspirated by the sampling device.
But what is considered a viable particle? A viable particle is a particle that contains one or more living microorganisms. These can affect the sterility of the pharmaceutical product and generally range in size from 0.2 micron to 30 microns (�m). These microorganisms often make use of a dust particle as a carrier mechanism and separation of the microorganism from the dust particle is a very sensitive but necessary process.
For impaction and impingement air samplers, the device selected should have the following characteristics regarding the impact velocity of the air hitting the culture medium, which should be a compromise between high enough to allow the entrapment of viable particles down to approximately 1�m and low enough to ensure viability of viable particles by avoiding mechanical damage or the break up of clumps of bacteria or micromycetes. Further, the sampling volume should be a compromise between being large enough to detect very low levels of biocontamination and being small enough to avoid physical or chemical degradation of the collection medium.
For areas of high biocontamination, the impaction method and sampling volume should be selected appropriately to achieve colony separation in order to allow the results to be interpreted. Thus, the device should meet the following requirements: sufficient flow rate to collect 1m3 in a reasonable time without significant dehydration of the sample media and appropriate air impaction speed to the culture media so that the microorganisms are not severely stressed. Severe stress to the microorganism causes delayed growth or microorganism death, which can provide a false sense of present air contamination.
Guidance for Selecting an Air Sampler
It is important to choose an air sampler that satisfies the requirements in ISO 14698. Systems are available that offer multipoint remote air monitoring and a compact air monitoring unit that utilizes impactor sampler technology, operating at low velocity (11 m/s), maintaining high collection efficiency while avoiding severe stress to microorganisms. This is achieved by laser technology that forms rectangular nozzles exactly 90 microns wide on the impactor head. Also, this allows interception of microorganisms that would normally lack sufficient sedimentation speed and would therefore escape observation while directing the microorganisms to be impacted on the on the media surface in a clearly distinguished pattern.
Impacted media plate with colonies defined in the impaction plane
As a result, this design provides a mechanism for differentiating between true contamination captured from within the air of the controlled environment versus erroneous contamination that is likely to be introduced by an external source.
In order to prevent re-contamination of the environment air, an inline 0.45 micron exhaust filter is used as air is ejected from the unit. Moreover, the system can be adapted to monitor air from compressed gases and isolators with available specialized kits.
Conclusion
In an effort to minimize liability, many pharmaceutical and biotechnology manufacturers have established guidelines for environmental monitoring, including air sampling. Continuous monitoring helps determine what levels of contaminants are acceptable and what levels of contamination may affect the quality of the product requiring intervention. However, environmental monitoring, in particular microbiological air monitoring, is often overlooked and subsequent contaminations are casually attributed to human error, such as improper aseptic techniques and inadequate cleaning agents. All of which may be true however, observing the contamination coming from the air needs to be heavily considered when troubleshooting a contamination issue or beginning a new process. In any event, the type of microbiological air sampler will play an important role in a successful environmental monitoring program. Further, the latest ISO 14698 standards facilitate the environmental monitoring process by providing techniques for the detection and monitoring of airborne biocontamination as well as the evaluation and qualification of the efficiency of air samplers. �
REFERENCES
ISO 14698-1:2003. "Cleanrooms and associated controlled environments - Biocontamination control."
ISO 14698-2:2003. Evaluation and interpretation of biocontamination data."
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