Patent Application
20170184475
The invention relates to microbial gaseous-fluid sampler and methods of operating the same. Microbial samplers are used, for example, to monitor for the presence of airborne microorganisms in controlled environments where contamination of a product being manufactured can render that product unsuitable for its intended purpose. As an example, pharmaceutical manufacturers maintain controlled environments and operate with procedures that reduce the risk of biological contamination. These environments where pharmaceutical products are formulated and packaged are regulated by government agencies to insure compliance to standards that specify a maximum number of viable organisms allowed to be present in a given volume of air collected from within the controlled environment.
One category of microbial samplers uses an impaction method, in which a known volume of air is drawn into the microbial sampler. Commonly, such microbial gaseous-fluid samplers are operable to capture bacteria, fungi, and other particles onto a Petri dish loaded with nutrient agar. After the given volume of air is sampled, the Petri dish is incubated and the microorganisms that are deposited on the agar and that are viable will form colonies. The colonies formed after incubation are counted to determine the concentration of colony forming units (CFU's). The number of CFU's is then compared to the allowable limit applicable to the process being performed.
In one aspect, the invention provides a microbial gaseous-fluid sampler for collecting microbial particles from gaseous fluid. The sampler includes a gaseous-fluid intake portion having a sample head with a plurality of holes. The gaseous-fluid intake portion further includes a collar configured to receive a Petri dish including agar. The plurality of holes define an exit plane that is positioned a distance from the agar within a range of 5.5 millimeters to 7.5 millimeters. The velocity of the air exiting the plurality of holes is within a range of 18.5 meters per second to 20. 5 meters per second.
In another aspect, the invention provides an intake portion for a microbial gaseous-fluid sampler. The intake portion includes a sample head with a plurality of holes arranged in a grid with separation between adjacent holes measuring within a range of 0.12 inches to 0.13 inches. The intake portion further includes a collar selectively interlocked with the sample head. The collar is configured to receive a Petri dish including agar. The plurality of holes define an exit plane that is positioned a distance from the agar within a range of 5.5 millimeters to 7.5 millimeters. The velocity of the air exiting the plurality to holes is within a range of 18.5 meters per second to 20.5 meters per second.
Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.
Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.
With reference to
The portable sampler 10 also includes an interface panel 45 for a user to operate the portable sampler 10 and to view information related to the portable sampler 10 and the samples collected by the portable sampler 10. The interface panel 45 includes a power button 50 generally configured to operate the portable sampler 10 between an “on” state and an “off” state. Depending on the configuration of the portable sampler 10, the power button 50 may operate the portable sampler 10 between other states, such as an “idle” state and a “power save” state. The interface panel 45 also includes buttons 55 operable to control other operating characteristics of the portable sampler 10, and LED lights 60 indicating, among other things, when the portable sampler 10 is in an “alarm” mode or when a sample has been collected. The LED lights 60 may be operable to indicate other modes or states of the portable sampler 10. The interface panel 45 also includes an LCD display 65 operable to display information related to the portable sampler 10 and the sample collected by the portable sampler 10. Other constructions of the portable sampler 10 can include different types of displays other than the LCD display 65. Moreover, other constructions of the portable sampler 10 can include different configurations for the interface panel 45.
In the construction shown in
The intake portion 40 shown in
U.S. Pat. No. 7,752,930, the entire content of which is incorporated herein by reference, disclose in detail example configurations of a control system and a gaseous-fluid flow system that create an airflow through the porous surface 110 of the intake portion 40 during operation. Generally, gaseous-fluid flow is generated by operating a blower assembly, which causes gaseous fluid to be sucked into the portable sampler 10 through the apertures defined by the cover 105. The configuration of the cover 105 causes gaseous fluid to engage a contact device (e.g., a Petri dish) in a direction substantially parallel to the axis Y. As explained further below, the contact device, generally supporting some type of nutrient agar, is allowed to receive or capture biologically active particles present in the gaseous fluid. Subsequently, gaseous-fluid flow continues from the surface of the contact device to the blower assembly and ultimately to an exhaust.
The improvement over the design shown in
With reference to
With reference to
With reference to
In the illustrated embodiment, an O-ring 268 is positioned between the mounting collar 218 and the sample head 214 for improved sealing. Although in alternative embodiments, the O-ring may be omitted. The mounting collar 218 is a solid machined part fabricated from 316L stainless steel. There are no springs or visible fasteners to the user, which make it possible for the mounting collar 218 to be easily sanitized by an operator wiping it down with a cloth and antimicrobial disinfectant. In addition, the sample head 214 is formed as such to be cleaned with no inaccessible pockets that would prevent sanitation by wiping the visible surfaces.
With continued reference to
With reference to
As explained further below, in some embodiments the invention provides for the critical combination of the distance 288 falling with the range of approximately 5.5 to 7.5 mm and the air velocity within the range of approximately 18.5 to 20.5 m/s to achieve unexpected improvements in the biological collection efficiency of the sampler utilizing the intake portion 210. In other words, the range of the distance 288 between the plurality of holes 230 and the agar 224 in combination with the air velocity significantly improves the efficiency of the sampler to collect biological specimens.
With reference to
The ability of a microbial sampler to collect microbes entrained in the sampled air can be measured by two main factors that are a function of impact velocity. Firstly, the impact velocity should be high enough to allow for the entrapment of viable particles down to approximately 1 μm. Secondly, the impact velocity should be low enough to ensure viability of particles by avoiding mechanical damage or the breakup of clumps of bacteria or micromycetes. In other words, the impact velocity of the air hitting the agar is a compromise between optimizing the two competing factors. See ISO standard 14698-1:2003(E).
The discussion presented below illustrates how in some embodiments of the invention the critical range of the distance 288 and the air velocity in the invention was unexpected since it conflicted with teachings common in the art.
Conventional microbial samplers that use the impaction method, employ a vacuum source such as a fan or blower that is built into the microbial sampler or an external vacuum source. The purpose of the vacuum source is to drawn a known volume of air (e.g., a cubic meter) through the sampling system at a known rate. The air enters the plurality of holes in a direction perpendicular to the agar. With the proper air velocity, the particles entrained in the air are impacted onto the agar as the air abruptly changes direction to flow around the Petri dish. Without the proper air velocity, the particles may continue their trajectory with the main airflow.
Testing the physical and biological collection efficiency of biological samplers requires specialized equipment and expertise. To make do without either the equipment or expertise, designers and manufacturers of biological samplers have traditionally applied theory to produce a variety of samplers. Independent third party studies have followed, which revealed that the actual performance of most samplers deviates unfavorably compared to the performance specified by the manufacturers. Evidence of the conventional designs having inferior performance is provided by, for example, Table 7 from the study of “Characteristics of Twenty-Nine Aerosol Samplers Tested at U.S. Army Edgewood Chemical Biological Center” (2000-2006).
Studies have also shown that calculations for predicting the performance of impactors using models of single jets and impact plates vary from the empirical results obtained on instruments that are designed with multiple jets. Evidence of this is provided by, for example, page 595 of the “Investigation of Cut-Off Sizes and Collection Efficiencies of Portable Microbial Samplers” (June 2006). In general, the study finds in most cases that the theoretical cut-off size (i.e., the size of particles too small for collection by the sampler) was lower than the experimental value. In other words, the theory incorrectly predicts the sampler is able to collect particles smaller than what is realistically achievable by the sampler.
The international standard, ISO 14698-1:2003 (E) establishes the principles and methodology for assessing biocontamination when cleanroom technology is applied for sterile manufacturing. The standard describes a testing technique, given as informative guidance and states that microbial sampler should have an impact velocity high enough to allow the entrapment of viable particles down to approximately 1 um and low enough to ensure viability of particles by avoiding mechanical damage.
The following series of tests were performed as part of arriving at the invention, with deviations from conventional teachings detailed.
Test 1—Determining Physical Collection Efficiency
Given the uncertainty of results when relying solely on theoretical engineering design choices, the physical collection efficiency was experimentally tested as a function of the distance between the sample head and the agar while the jet velocity is constant. Two different particle sizes of interest were used: 1 μm and 5 μm. For this test the jet velocity was held constant at 12.5 meters per second and a conventional sample head was used with 333 holes, each with a diameter of 0.028 inches arranged in a grid with a separation of 0.125 inches. The particles in the challenge aerosol were generated using a vibrating orifice aerosol generator to produce droplets of a saline solution of a known volume. The droplets yield salt particles of a known diameter when the liquid portion of the droplet evaporates.
With reference to
Test 2—Determining Biological Collection Efficiency
The next step of testing, after the physical collection efficiency, is to determine the biological collection efficiency. A bacterium, Staphylococcus saprophyticus, having a diameter of 0.6 to 1.4 μm was used as a challenge aerosol. A biological sampler using liquid impingement collection method and having an independently certified collection efficiency of 100% was used as a reference.
The sampler operates with a volumetric air flow rate passing through the plurality of holes of 100 liters per minute (LPM). For this test, the air velocity remained at 12.5 m/s and the distance was set to 9.18 millimeters, and resulted in a measured biological collection efficiency of 83%, which was better than expected since the biological collection efficiency exceeded the physical collection efficiency measured for the 1μm particles (see FIG. 13). The biological collection efficiency being larger than the physical collection efficiency was attributed to the higher density of the bacterium particle itself, compared to that of the salt used in the physical collection test.
Conventional teachings provided by “Effect of Impact Stress on Microbial Recovery on an Agar Surface” (1995) states that when the height between the impaction surface and the nozzle plane is larger than the width of the nozzle, the collection cutoff size is only moderately affected by variations in distance. This study also reported an injury rate for of 31±19% and 39±14 for P. fluorescens and M. luteus, respectively, when using an impaction velocity of 24 m/s.
The higher biological collection efficiency from Test 2 was in contrast with conventional theory since in order to achieve an 83% biological collection efficiency with an expected physical collection efficiency of less than 83%, the injury rate would have had to be negligible. This led to the discovery from the biological collection efficiency test that the microbes were not being injured at a measurable rate. The lower than expected injury percentage is attributed to the lower impaction velocity of initial designs (12.5 m/s) compared to the lowest velocity used in the study noted above (24 m/s).
Test 3—Reducing the Distance Between the Hole Exit Plane to the Agar
With the strong positive affect that the distance had on the 5 μm physical collection efficiency and the higher than expected biological collection efficiency, the next step was to conducted an experiment to measure the biological collection efficiency with the same velocity (i.e., 12.5 m/s) while reducing the distance from 9.19 mm to 6.5 mm. The biological collection efficiency increased from 83% to 96% with the reduction in the distance to 6.5 mm. This result contradicted the theoretical prediction for physical collection efficiency which predicted only a moderate affect for the variation of the distance. This result also indicated that the reduced distance did not adversely affect the viability of the microbes impacting the agar.
Test 4—Reducing Hole Diameter to Increase Impaction Velocity
The next test utilized the intake portion 210 according to an embodiment of the invention with the sample head 214 having the plurality of holes 230 with a diameter of 0.0225 inches, which produced an impaction velocity of 19.5 meters per second and kept the distance 288 to 6.5 mm. Testing of the invention showed the biological collection efficiency increased to 101%. Although it is theoretically impossible to achieve efficiency greater than 100%, the difference can be attributed to the flow rate tolerances of ±2% applicable to both the reference sampler and the unit under test. This test result again contradicted the conventional teachings that predicted a higher injury percentage for higher impaction velocities. Granted, the impaction velocity for Test 4 was still lower (19.5 m/s) than the lowest impaction velocity in the published study referenced above (24 m/s).
In view of the above, some embodiments of the invention provide the combination of the critical distance 288 and the air velocity in the intake portions 210 and 310 that unexpectedly improved the biological collection efficiency. This improvement in the performance of the microbial sampler has not been accomplished previously by the application of theoretical engineering design choices applied in other microbial samplers currently on the market.
This application claims priority to co-pending U.S. Provisional Patent Application No. 62/272,472, filed on Dec. 29, 2015, the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62272472 | Dec 2015 | US |
