Identification of normal flora, spoilage organisms, clinical and food-borne pathogens, starter cultures, etc. In the past 25 years, many miniaturized diagnostic kits have been developed and widely used to conveniently introduce the pure cultures into the system and obtain reliable identification in as short as two to four hours. Some systems can handle several or even hundreds of isolates at the same time.
These diagnostic kits no doubt saved many lives by rapidly, accurately and conveniently identifying pathogens so that treatments can be made correctly and rapidly. There are no less than 20 miniaturized systems on the market to identify pathogens ranging from enterics Salmonella, Shigella, Proteus, Enterobacter, etc.
Antigen and antibody reaction has been used for decades for detecting and characterizing microorganisms and their components in medical and diagnostic microbiology. This is the basis for serotyping bacteria such as Salmonella, Escherichia coli OH7, Listeria monocytogenes, etc. Both polyclonal antibodies and monoclonal antibodies have been used extensively in applied food microbiology.
Recently, some companies have completely automated the entire ELISA procedure and can complete an assay from 45 minutes to two hours after overnight incubation of the sample with suspect target organisms. Lateral Flow Technology similar to pregnancy test with three detection areas on a small unit offers a simple and rapid test for target pathogens e. The entire procedure takes only about ten minutes with very little training necessary.
A truly innovative development in applied microbiology is the immuno-magnetic separation IMS system. Very homogenized, paramagnetic beads have been developed, which can be coated with a variety of molecules, such as antibodies, antigens, DNA, etc.
These beads can then be immobilized, captured and concentrated by a magnet stationed outside a test tube. After clean-up, the beads with the captured target molecules or organisms can be plated on agar for cultivation or used in ELISA, Polymerase Chain Reaction PCR , microarray technologies, biochips, etc. Instruments can be used to automatically monitor changes such as ATP levels, specific enzymes, pH, electrical impedance, conductance, capacitance, turbidity, color, heat, radioactive carbon dioxide, etc.
It is important to note that, for the information to be useful, these parameters must be related to viable cell count of the same sample series. In general, the larger the number of viable cells in the sample, the shorter the detection time of these systems. A scatter gram is then plotted and used for further comparison of unknown samples. The assumption is that, as the number of microorganisms increases in the sample, these physical, biophysical and biochemical events will also increase accordingly.
Some instruments can handle hundreds of samples at the same time. Phenotypic expressions of cells are subject to growth conditions such as temperature, pH, nutrient availability, oxidation-reduction potentials, etc. Genotypic characteristics of a cell are far more stable. By use of reverse transcriptase, target RNA can also be amplified and detected.
University College Cork
After a DNA double stranded molecule is denatured by heat e. A polymerase TAQ will extend the primer at a higher temperature e. After one thermal cycle, one piece of DNA will become two pieces. After 21 and 31 cycles one piece will become 1 million and 1 billion copies, respectively.
Where microbiology makes a difference
At the beginning, PCR products are detected by gel electrophoresis. Ingenious ways exist to detect either the occurrence of the PCR procedure by fluorescent probes or special dyes, or by actually reporting the presence of the PCR products by molecular beacon. Some systems can monitor four different targets in the same sample multiplexing. These methods are now standardized and easy to use and interpret. Since different bacteria exhibit different patterns e. Salmonella versus E. Listeria monocytogenes has 49 distinct patterns , these information can be used to compare closely related organisms for accurate identification of target pathogens such as comparing different patterns of E.
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Biosensor is an exciting field in applied microbiology. The basic idea is simple but the actual operation is quite complex and involves much instrumentation. Basically, a biosensor is a molecule or a group of molecules of biological origin attached to a signal recognition material. When an analyte comes in contact with the biosensor, the interaction will initiate a recognition signal which can be reported in an instrument.
Many types of biosensors have been developed. Sometimes, whole cells can be used as biosensors. Analytes detected include toxins, specific pathogens, carbohydrates, insecticides and herbicides, ATP, antibiotics, etc.
The recognition sig-nals used include electrochemical e. Due to the advancement in miniaturization technology, as many as 50, individual spots e.
DNA microarrays , with each spot containing millions of copies of a specific DNA probes can be immobilized on a specialized microscope slide. Fluorescent labeled targets can be hybridized to these spots and be detected. British Wildlife is the leading natural history magazine in the UK, providing essential reading for both enthusiast and professional naturalists and wildlife conservationists. Published six times a year, British Wildlife bridges the gap between popular writing and scientific literature through a combination of long-form articles, regular columns and reports, book reviews and letters.
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Advances in Applied Microbiology, Volume 70 - 1st Edition
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