MOLECULAR TECHNIQUES IN MICROBIOLOGY (1) Standard polymerase chain reaction Kary Mullis invented the PCR in 1983 (USA)Kary Mullis and synthesized short chains of DNA. Given Nobel Prize in Chemistry in He invented a method of amplifying DNA through repeated cycles of duplication driven by DNA polymerase PCR technique used an automated process for DNA amplification & separation of the DNA strands.

PCR Components and DNA template that contains the DNA fragment to be Two Primers that are complementary to the 3' (three prime) ends of each of the sense and anti-sense strand of the DNA Deoxynucleoside triphosphates (dNTPs), the building-blocks from which DNA polymerase synthesizes a new DNA strand.

@ Taq DNA polymerase with a temperature optimum at around 70 Buffer solution, providing a suitable chemical environment for optimum activity and stability of the DNA Divalent cations (magnesium or manganese) for DNA Monovalent cation (potassium) for DNA synthesis

PCR PCR is a biochemical technology to amplify a single or a few copies of a piece of DNA to generate millions of copies of a certain DNA The technique depends on thermal cycling, with repeated heating and cooling to melt and amplify (replicate) the Repeated amplification of DNA requires short DNA fragments (Primers) and a heat- stable DNA polymerase (Taq polymerase) obtained from bacterium Thermus aquaticus.

A thermal cycler for PCR

@ This DNA Taq polymerase enzyme assembles a new DNA strand from DNA nucleotides primers by using the single stranded DNA present in the reaction as a Thus DNA synthesis is initiated and a chain of reactions develops, resulting in massive DNA amplification.

PCR PCR consists of a series of repeated temp. changes, called cycles, each cycle consists of 2-3 temp. These cycles is preceded by a single temp. step (called hold) equaling >90°C, and followed by another hold temp. at the The temp. used and the length of time they are applied in each cycle depend on: # The enzyme used for DNA synthesis # The concentration of divalent ions and Deoxynucleoside triphosphates (dNTPs). # The melting temp. (Tm) of the primers.

Initialization step: This step consists of heating the reaction to a temp. of 94–96°C and held for 1–9 minutes. Denaturation This step consists of heating the reaction to 94–98°C for 20–30 It causes DNA melting of the DNA template yielding single-stranded DNA molecules. Annealing step: The reaction temp. is lowered to 50–65°C for 20–40 sec. to allow annealing (attaching) DNA primers to the single stranded DNA template

Extension/elongation The temp. at this step is 75–80°C which is required by the Taq DNA This DNA polymerase synthesizes a new DNA strand similar to the DNA template This is done by adding dNTPs to the template in 5' to 3' direction, then replaces the 5'-phosphate group of the dNTPs with the 3'-hydroxyl group at the end of the chain to extend DNA At each extension step, the DNA amount is doubled, leading to exponential (geometric) amplification of the DNA fragment.

PCR cycle. (1) Denaturing (2) Annealing (3) Elongation. Blue lines represent DNA template to which primers (red arrows) anneal; extended by DNA polymerase (light green circles); to give shorter DNA products (green lines); which themselves are used as templates as PCR progresses.

Final elongation step: This step is performed at a temp. of 70–74°C for 5–15 minutes to ensure that any remaining single-stranded DNA is fully extended. Extension/elongation This step is performed at 4–15°C for an indefinite It is used for short-term storage of the reaction.

@ To check whether PCR generated good amplification agarose gel electrophoresis is employed for size separation of the PCR The size of PCR products is determined by comparison with a DNA ladder (a molecular weight marker), which runs on the gel alongside the PCR products.

PCR products after gel electrophoresis. No amplification in sample 1; Sample 2 & 3 indicate amplification; Positive control & DNA ladder are shown

False PCR: Contamination causes false amplification of DNA products. This is prevented Separation of PCR area from areas for analysis or purification of PCR Use of disposable plastic Thorough cleaning of the work surface between reaction Proper primer design techniques by using electronic Usage of other buffers and polymerase enzymes.

PCR DNA extraction : From cell genome DNA by selective amplification of a specific region of DNA. This is done by hybridization probes and DNA cloning, to create copies of DNA DNA sequencing: To determine unknown PCR-amplified sequences by the insertion of a DNA sequence into a genetic material of another DNA-based phylogeny: To determine the evolutionary relationships among organisms.

@ Amplification and quantification of DNA: To estimate the amount of a given sequence present in a sample (gene expression), using Real-time Identification of uncultivable or slow- growing organisms: Such as mycobacteria, anaerobic bacteria, or Early diagnosis of infectious diseases: Such as leukemia and lymphomas; detecting malignant cells at a high sensitivity.

Genes are expressed by being transcribed into RNA, and this RNA transcript is then translated into protein

@ Quantification viral load in a patient Diagnosis of hereditary Identification of genetic fingerprints. This is used in forensic sciences and paternity testing

Paternity fingerprints (1) Father. (2) Child. (3) Mother.

(2) Real-time Also called quantitative real time PCR It is a laboratory technique based on the PCR technique that is used to amplify and quantify a DNA In a DNA sample, qPCR enables at the same time both detection and Its procedure is same as PCR, But in qPCR the amplified DNA is detected as the reaction progresses in real time qPCR technique can either use non-specific fluorochromes or hybridization probes

Applications of Clinical quantification and Quantification of microbial load in foods or on Rapid detection of cancer, newly emerging diseases, and genetic Microbial assessment of water Quantitative measure of gene Production of plant seedlings that are free of pathogens.

Other Molecular Techniques: 1.DNA sequencing and genome data: Used to analyze the bacterial DNA sequence and mapping all its genome data. 2. RNA interference: Used for gene silencing in biological research and drug discovery s rRNA sequencing: Used for bacterial identifications

Automated Genetic Analyzer for complete genome sequencing.

4. DNA Used as the alternative to the "blotting" This technique can detect the presence of pathogens in a It can determine the genetic differences between two microbial strains. 5. Gel electrophoresis: Used to separate DNA, RNA, or protein molecules by an electric field by virtue of their size, shape or electric charge.

6. Direct gene detection: Used to detect genes related to drug resistance mechanisms, such as mecA gene in Staphylococcus aureus 7. Pulsed Field Gel Electrophoresis: Used for bacterial typing to trace source of infection