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 from ~0.2µm to ~30µm in size.
Monitoring of Viable Particle:- The method of monitoring these particles is by capturing, colonizing and counting them. Two technologies are used.
(1) Settled Plates:- These 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, collected after several hours, incubated, and the resulting colonies counted, based on the area of the surface on which they were collected in addition to the period of time the sample was taken.
(2) Air Samplers:- Used to sample microorganisms in air. The volume sampled is usually 1 m3 or cfu/m3.
The method of collecting the microorganisms is by impaction. The sampling head of the air sampler is en gineered in such a way that the delivery of the sample to the contact plate, or agar strip, is delivered so as not to disrupt normal ambient airflow and more importantly without rendering the microorganism non-viable. This has become an area of interest as it had been previously overlooked and was recently outlined in ISO 14698-1: 2003. The contact plates, agar strips or filter membrane are then incubated and the resulting colonies are counted under a microscope and the type of bacteria is also identified.
Non-viable particle:- A non-viable particle is a particle that does not contain a living microorganism but acts as transportation for viable particles.
Monitoring of Non-Viable Particle:- Non-viable particles are monitored using particle counters which do not distinguish between viable and non-viable particles but are much more technically advanced than air samplers. Particle counters were developed by the U.S. Military in the 1960s for use in the aerospace industry and were then further developed for use in the semiconductor and pharmaceutical industries. They consist of a dark chamber, or sensor, containing a discrete laser which uses mirrors and optics to view the particle, and a pump to pull the required sample through the sensor. The principal behind the detection and sizing of particles is simple; the vacuum pump sucks the particle through the sensor and the laser beam. At this stage it deflects the light from the laser onto mirrors which are focused onto a photo detector; this reflected light is then converted into an electrical pulse by the photo detector. The pulses are counted and sized by the electronics within the particle counter. The bigger the particle the more light it reflects and therefore the bigger the electrical pulse converted by the photo detector.
Sampling of Non-Viable Particle:- The particles are sampled using a selected volume of air. Because particle counters were first developed and manufactured in the U.S., the first standards developed were imperial and a sample volume of 1 cubic foot became accepted internationally as the standard volume, as it conveniently took 1 minute to complete. However, a lot of countries developed their own standards and countries in Europe used metric volumes so the 1 cubic meter sample came about. Depending on what standard is followed, the sample is taken and the concentration of particles per volume is displayed on the screen of the particle counter. Normally the size of particle is shown with the corresponding number of particles. The pharmaceutical industry is mostly interested in the reporting of two sizes: =0.5µm and =5.0µm, as these ranges contain the microorganisms that will have an adverse effect on the sterility of the product.
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