N.43 – Available microbial air samplers for airborne microorganisms.


The USP 38 – The United States Pharmacopeial Document – Official from May 1, 2015 – presents on page 1200 the list of the most commonly used tools for monitoring aseptic environments.


The unit is powered by an attached source of controllable vacuum. The air intake is obtained through a standardized slit below which is placed a slowly revolving Petri dish that contains a nutrient agar. Airborne particles that have sufficient mass impact the agar surface, and viable microorganisms are allowed to grow. A remote air intake is often used to minimize disturbance of unidirectional airflow.


This apparatus consists of a container designed to accommodate a Petri dish that contains a nutrient agar. The cover of the unit is perforated with opening of a predetermined size. A vacuum pump draws a known volume of air through the cover, and airborne particles that contain microorganisms impact the agar  medium in the Petri dish. Some samplers feature a cascade series of sieves that contain perforation of decreasing size. These units allow determination of the size range distribution of particulates that contain viable microorganisms based on the size of the perforations through which the particles landed on the agar surface.


The unit is a variant of the single stage sieve impactor. The unit’s cover contains uniformly spaced orifices approximately 0.25 inch in size. The base of the unit accommodates one Petri dish containing a nutrient agar. A vacuum pump controls the movements of air through the unit.


The unit consists of a propeller or turbine that pulls a known volume of air into the unit and then propels the air outward to impact on a tangentially placed nutrient agar strip set on a flexible plastic base.


The integrated unit consists of an entry section that accommodates an agar contact plate. Immediately behind the contact plate is a motor and turbine that pulls air through the unit perforated cover over the agar contact plate and beyond the motor, where it is exhausted. Multiple mounted assemblies are also available.


The unit consists of a vacuum pump with an extension hose  terminating in a filter holder that can be located remotely in the critical space. The filter consists of random fibers of gelatin capable of retaining airborne microorganisms. After a specific exposure time, the filter is aseptically removed and dissolved in an appropriate diluent and then plated on an appropriate agar medium to estimate its microbial content.


The method is still widely used as a simple and inexpensive way to qualitatively assess the environments over prolonged exposure times. Published data indicate that settling plates, when exposed for 4-to-5-hour periods,  can provide a  limit of detection for a suitable evaluation of the aseptic environment. Settling plates may be particularly useful in critical areas where active sampling could be intrusive and hazard to the aseptic operation.