Rapid microbiological tests and reagents are gaining momentum in the global economic market as a reliable and cost-effective method to track and monitor all types of microorganisms in clinical as well as industrial settings. In addition, faster and more accurate methods are emerging annually to assist in the rapid diagnosis and treatment of patients or to provide safe and reliable food, water, and pharmaceuticals. Expeditious reporting helps to reduce the chance of disease transmission in patient settings or outbreaks through contaminated food or medical supplies.
It is difficult to ascertain the extent of laboratory testing performed annually in the clinical setting, but it is believed that the U.S. and Europe constitute approximately two-thirds of all microbiological testing procedures. The rest of the world covers the remaining third, but with populations soaring in Asia, India, and other regions, the market is wide open for advancing rapid diagnostic technologies to improve patient management: exponential population growth and aging conventional technology will only intensify the pace of development. The market potential is pressed further by the continual need to identify novel and emerging pathogens and antibiotic resistance mechanisms by a growing number of bacteria. Like the organisms they identify, rapid microbiological testing methods need to be dynamic, versatile and easy to integrate into existing platforms. They also need to be cost-effective for the emerging global economy. Novel technology is valuable only when put to practical use, so if laboratories, communities, and countries are unable to afford new rapid methods, they are of little use in real-world applications.
Forecasters believe that traditional microbiological methodology, though still the predominant testing mechanism, will decline over the next few years, while the demand for rapid test and reagent options will be on the rise. The term “rapid test method” simply describes a variety of detection and identification tests, from those that take only a few minutes to perform to those that may require days. Rapid is a relative term; essentially, it refers to a faster method than conventional enrichment and culture-based testing.
Rapid microbiological tests and reagents run the gamut from simple biochemical or immunological techniques to direct specimen tests to a combination of sophisticated instrumentation, software, consumables, and reagents. Specific detection, quantitative, or identification methodologies may be employed, depending upon the desired approach, epidemiological significance, and degree of identification required. Arguably, many of the current rapid tests and reagents on the market today require that a relatively large number of living microbial cells be present in the sample, and that means traditional enrichment and culture must first be employed. Moreover, since testing may be performed in a variety of locations—doctors’ offices, hospital settings, or research and reference labs—it is important to understand the technical capabilities that are required. Those include the method sensitivity and specificity (for example, limits of detection and target microorganisms), expectations of the system or method, and the degree of training required of the operator.
One type of common rapid test method involves the use of miniaturized biochemical identification devices. These disposable devices perform a range of biochemical tests simultaneously—usually eight to 24 tests—using a microwell strip format. They are generally designed to identify specific bacterial species. A microbiologist must work with a pure culture, and some test kits can provide results within four to 24 hours. These units simplify conventional testing procedures by eliminating the need for multiple tubed or plated media; they are generally space, time, and cost savers.
Other types of rapid identification kits speed up standard testing methods by using special substrates, enzymes, or a similar format apparatus. They may include specific biochemical reactions that help to identify organisms of interest. These tests may incorporate a disk, card, strip, or medium impregnated with a specific chemical or chemicals that react in the presence of a particular microorganism. In general, they may utilize a colorimetric reaction to demonstrate a specific response and to differentiate the organism of interest from other flora. Additionally, card format kits can be used to incorporate more than one type of reaction, thereby simplifying the setup and expanding the volume of results.
Some rapid tests and reagents involve using antibodies or nucleic acids to detect pathogens or toxins. Of these, antibodies are the most versatile and may be used in a variety of kits. These rapid kits take advantage of antibody-antigen interactions unique to a particular microorganism. A latex agglutination test works in this manner: beads are coated with plasma antibodies unique to a particular pathogen. If the reaction turns positive, the latex beads will cause the bacterium to clump or agglutinate. If the beads are colored and are placed on a white background, it is easy to detect a positive reaction by observing visible clumping, usually within a matter of seconds.
Enzyme-linked immunosorbent assays (ELISA) and enzyme immunoassays (EIA) rely on antibody-antigen interactions which can be placed on a microplate or combined on a membrane and incorporated into a lateral flow kit. Antibody screening and toxin tests are examples of these types of kits and are most useful for direct specimen testing when a result is needed quickly to aid in the diagnosis of disease.
Polymerase chain reaction-based kits (PCR) use an enzyme to replicate a small portion of a target microorganism’s DNA. The reaction involves attaching a marker to the target DNA so that it is more easily visualized. The advantage of this rapid test format is that very small numbers of a pathogen can be detected rather quickly. However, PCR-based methods cannot distinguish between viable and nonviable cells, so results must be interpreted accordingly.
These are just a few examples of what rapid test and reagent kits can do, but the goal of rapid testing is the same no matter the application: to provide accurate identification and rapid communication to interested parties in order to improve outcomes. Cost may be the main downside to some of the newest forms of rapid tests: there is a price to pay for research and development and to promote innovative technologies. For larger laboratories, economics of scale and reduced labor costs may offset the cost per test: speedy results carry a cost benefit. Conversely, costs may be significant enough to put some of the more recent high-tech rapid methods out of reach for smaller laboratories, especially when there is no foreseeable cost benefit in results or if the reading window does not fit into a smaller laboratory’s scheduling restrictions. However, demand and competition generally bring costs down—emerging facets of a dynamically changing market economy—so it is only a matter of time before advancing technologies become cost-effective on a global scale.
CarboFerm™ I Neisseria Kit for the rapid identification of Neisseria spp. and Moraxella catarrhalis within four hours.
Center: OxiDrop™, Oxidase Test is a ready-to-use reagent to rapidly detect cytochrome c oxidase activity in bacteria within 10 to 20 seconds.
Nitrocef Matchbook™ sticks are for rapid identification of beta-lactamase production capable of inactivating penicillinase-labile-penicillins in Neisseria gonorrhoeae, Moraxella catarrhalis, Staphylococcus spp., Haemophilus influenzae, Enterococcus spp., and some anaerobic bacteria. Most results are detected within five minutes.
Kerry Davies Pierce, MS, is Technical Support Specialist for Santa Maria, California-based Hardy Diagnostics, a manufacturer and distributor of rapid test kits and other microbiological supplies.
