Youtube Of Indentification Of The Bactetial Unknow?

Objective:

To identify the bacterial unknowns in a mixed civilization by morphological and biochemical methods.

Principle:

The identification of bacteria is a careful and systematic process that uses many unlike techniques to narrow down the types of bacteria that are present in an unknown bacterial culture. It produces benefits for many aspects of the inquiry of microorganisms and helps physicians correctly treat patients. Multiple tests were performed to provide the fermentation abilities, presence of certain enzymes, and certain biochemical reactions. Qualitative observations were made on the tests, which were compared to unknown bacteria identification primal to aid with the identification procedure.

Various steps involved in the identification of unknown bacteria are:

Isolation:

The importance of this pace is to isolate pure colonies of bacteria. The streak plate is a qualitative isolation method; quadrant streaking is mostly washed to obtain pure colonies. The inoculation of the culture is made on the agar surface by dorsum and forth streaking with the inoculation loop over the solid agar surface. This will brand a dilution gradient beyond the agar plate. Upon incubation, individual colonies will arise from the biomass.

The characteristics features of the colonies on solid agar media are then noted. This include

Shape : circular, irregular or rhizoid.
Size: minor, medium, big( or in millimetres).
Elevation: elevated, convex, concave, umbonate/umbilicate.
Surface: Smooth, wavy, rough, granular, papillate or glistening.
Edges: unabridged, undulate, crenated, fimbriate or curled.
Colour: Yelow, green etc.( Note the colour of the colony).
Structure: opaque, translucent or transparent.
Degree of growth : scanty, moderate or profuse.
Nature: discrete or confluent, filiform, spreading or rhizoid.

In gild to obtain the pure culture of organism, the isolated colonies are aseptically transferred on to dissimilar nutrient agar slant tubes and incubated overnight at 37 degree Celsius. It is then stored for future purpose.

Staining Reactions:

Staining is a elementary bones technique that is used to place microorganisms. Simple staining is used to report the morphology of all microorganisms (Fig 1). The elementary stain uses the basic dyes such as Methylene bluish or basic fuschin. The potent negative charge of the bacterial cell will strongly bind with the positive charged bones dyes and will impart its colour to all bacteria.

Fig 1: Simple staining of cocci

Gram staining is a differential staining technique that imparts different colours to dissimilar bacteria or bacterial structures. Usually information technology differentiates bacteria into two groups; gram positive and gram negative. The main stain Crystal violet and mordent Iodine grade a strong CVI complex all bacteria. Gram positive cells due to their thick peptidoglycan layer will retain the CVI complex even afterward information technology is subjected to decolourization with acetone or alcohol. Hence the counter stain Safranin has no action on gram positive cells. But in the case of gram negative, the thin peptidoglycan layer and more than lipid contents in the cell wall volition hands make them susceptible to the action of decolorizer and hence CVI complex is hands done out and hence the gram negative cells will the colour of counter stain Safranin. Hence after the gram staining, the gram positive cells announced as purple and gram negative cells appear every bit pink (Fig 2). The written report of morphological features and staining characteristics help in the preliminary identification of the isolate.

Fig 2: Gram positive bacteria Fig 2: Gram negative bacteria

Biochemical reactions:

Gram negative enteric bacilli play an important role in the contagion of nutrient. Hence they are the chief causative agents of intestinal infection. Gram negative family includes Shigella, Salmonella, Proteus, Klebsiella,Escherichia,Enterobacter etc. Usually four tests are used for differentiation of the various members of Enterobactericeae. They are Indole test,Methyl red exam, Voges proskauer test and Citrate test; collectively known equally IMViC series of reactions.

Indole exam:

Indole tests looks for the presence or absenteeism of tryptophanase enzyme production of the leaner. If the enzyme is present, it will degrade the aminoacid tryptophan in the media and will produce Indole, ammonia and pyruvic acrid. Indole volition react with Kovac's reagent to produce a ruby-red red complex, which indicates a positive indole examination. The absence of red color is indicative of tryptophan hydrolysis due to the lack of tryptophanse enzyme(Fig three).

Fig 3: Indole test

Methyl Ruby Test:

This test detects the power of microorganism to ferment glucose and to produce acidic stop products. Enteric organism produces pyruvic acrid from glucose metabolism. Some enteric will then employ the mixed acid pathway to metabolize pyruvic acid to other acidic products such as lactic acid, acetic acid and formic acids. This will reduce the pH of the media. Methyl scarlet is a pH indicator which is ruby-red at the acidic pH (below iv.4) and xanthous at element of group i pH (higher up 7). The germination of red color after the add-on of Methyl carmine reagent indicates the accumulation of acidic cease products in the medium and is an indicative of positive test (Fig iv).

Fig four: Methyl cherry test

Voges Proskauer Test:

This exam determines the power of microorganism to ferment glucose. The end products of glucose metabolism,pyruvic acid, is further metabolized by using Butylene glucol pathway to produce neutral end such every bit acetoin and two,3 butanediol. When Barrit'southward reagent A ( 40% KOH) and Barrit's reagent B (v% solution of alpha naphthol) is added it volition detect the presence of acetoin, the precursor in the 2,3- butanediol synthesis. Acetoin in the presence of Oxygen and Barrit's reagent is oxidized to diacetyl, where blastoff naphthol act as a catalyst. Diacetyl so reacts with guanidine components of peptone to produce a cherry red color (Fig 5).

Fig 5: Voges prausker test

Citrate Utilization Test:

This test determines the ability of microorganism to utilise Citrate. Some bacteria have the adequacy to convert the salts of organic acids, for example, Sodium citrate to alkali metal carbonates. Sodium citrate is 1 of the important metabolite of Kreb's cycle. Sure leaner utilize citrate as the sole carbon source. Citrate utilization requires a specific membrane transporter and citrate lyase activity. Citrate is converted to Oxalo acetic acid by citrate lyase and oxaloacetate decarboxylase activeness will convert oxaloacetate to pyruvate with the release of carbondioxide. The other products of the reaction are acetate, Lactic acid, formic acid etc. The carbondioxide reacts with sodium and water to form sodium carbonate (Fig 6).

Fig half dozen: Citrate test

TSI:

The triple sugar- iron agar test is designed to differentiate among the dissimilar groups or genera of the Enterobacteriaceae, which are all gram negative bacilli capable of fermenting glucose with the production of acrid, and to distinguish them from other gram negative intestinal bacilli. This differentiation is based on the differences in carbohydrate fermentation patterns and hydrogen sulfide production past the various groups of intestinal organisms. Carbohydrate fermentation is detected by the presence of gas and a visible colour modify (from red to yellowish) of the pH indicator, phenol ruby-red. The production of hydrogen sulfide is indicated by the presence of a precipitate that blackens the medium in the butt of the tube. TSI Agar contains 3 fermentative sugars, lactose and sucrose in 1% concentrations and glucose in a concentration of 0.1%. Due to the building of acid during fermentation, the pH falls. The acrid base indicator Phenol cerise is incorporated for detecting saccharide fermentation that is indicated by the modify in color of the medium from orangish carmine to yellow in the presence of acids. In case of oxidative decarboxylation of peptone, alkaline products are built and the pH rises. This is indicated by the change in colour of the medium from orange cerise to deep red. Sodium thiosulfate and ferrous ammonium sulfate present in the medium detects the product of hydrogen sulfide (indicated by blackening in the butt of the tube). To facilitate the detection of organisms that merely ferment glucose, the glucose concentration is i-10th the concentration of lactose or sucrose. The small amount of acrid produced in the slant of the tube during glucose fermentation oxidizes quickly, causing the medium to remain orange red or revert to an alkali metal pH. In dissimilarity, the acrid reaction (xanthous) is maintained in the barrel of the tube since it is under lower oxygen tension. Later depletion of the express glucose, organisms able to practise so will begin to utilize the lactose or sucrose. To enhance the alkaline condition of the slant, costless exchange of air must be permitted by closing the tube cap loosely. If the tube is tightly closed, an acid reaction (acquired solely by glucose fermentation) will as well involve the slant.

Urease test:

Urea is a nitrogen containing chemical compound that is produced during the decarboxylation process of the amino acrid arginine in the urea cycle. Urea is highly soluble in h2o and is thus it is an efficient way for the homo body to excess nitrogen. This backlog urea is then taken abroad from the torso with the help of the kidneys as a part of urine. Sure bacteria produce the enzyme urease during its metabolism process and that volition break downwards the urea in the medium to ammonia and carbon dioxide:

Some enteric bacteria produce the enzyme urease, which splits the urea molecule into carbon dioxide and ammonia. The urease test is useful in identifying the genera Proteus, Providentia, and Morganella, which liberate this enzyme.

Urease, which is produced by some micro organisms, is an enzyme that is especially helpful in the identification of Proteus vulgaris, although other organisms may produce urease, their activity on the substrate urea tends to exist slower than that seen with Proteus species. Therefore this test serves to rapidly distinguish members of this genus from other lactose not fermenting enteric micro organisms.

Urease is a hydrolytic enzyme that attacks the nitrogen and carbon bond in amide compounds such as urea and forms the alkaline finish product ammonia. The presence of urease is detectable when the organisms are grown in a urea broth medium containing the pH indicator phenol red. As the substrate urea is split into its products, the presence of ammonia creates an alkaline surroundings that causes the phenol ruby to plow to deep pink. This is a positive reaction for the presence of urease. Failure of deep pink color to develop is show of a negative reaction.

SIM:

The ability of an organism to move by itself is chosen move. Movement is closely linked with chemotaxis, the ability to orientate along certain chemical gradients. Eucaryotic cells can movement by ways of different locomotor organelles such every bit cilia, flagella, or pseudopods. Prokaryotes move by means of propeller-similar flagella unique to bacteria or by special fibrils that produce a gliding form of motility. About all spiral bacteria and almost one-half of the bacilli are motile, whereas essentially none of the cocci are motile.

The medium mainly used for this purpose is SIM medium ( Sulphide Indole Motility medium) which is a combination differential medium that tests three dissimilar parameters, sulphur reduction, indole production and motion. This media has a very soft consistency that allows motile bacteria to drift readily through them causing cloudiness. In soft agar tubes non-motile leaner volition only grow on the inoculated region. Motile bacteria volition grow along the stab line and will tend to swim out away from the stabbed surface area. Therefore, a negative consequence is represented by growth in a distinct zone directly along the stab. A positive outcome is indicated by diffuse or cloudy growth mainly at the top and lesser of the stabbed region.

SIM agar may also be used to notice the presence of H_twoDue south product. The SIM medium contains peptones and sodium thiosulfate as substrates, and ferrous ammonium sulfate, Atomic number 26(NH₄)So₄, every bit the H₂Southward indicator. Cysteine is a component of the peptones used in SIM medium. Sufficient agar is present to make the medium semisolid. Once H_iiDue south is produced, information technology combines with the ferrous ammonium sulfate, forming an insoluble, black ferrous sulfide precipitate that tin can be seen forth the line of the stab inoculation. If the organism is too motile, the entire tube may turn black. This black line or tube indicates a positive H₂Due south reaction; absence of a black precipitate indicates a negative reaction.

Gelatin Hydrolysis Test:

Gelatin, a protein derived from the animal protein collagen. It has been used as a solidifying agent in nutrient for a long time. Robert Koch used nutrient gelatin as an early on blazon of solid growth medium. One problem is that many bacteria have the ability to hydrolyze (liquefy) gelatin. This gelatin liquefaction ability (or disability) forms the footing for this examination. Some microorganisms possess an enzyme chosen gelatinase, which breaks down gelatin into amino acids. Gelatin deeps contain the substrate gelatin, which is a protein produced past the hydrolysis of collagen. Organisms which hydrolyze gelatin volition cause the gelatin to liquefy.

The gelatin hydrolysis tests for an organism's ability to break downwardly the protein gelatin which is derived from collagen. Gelatin causes the media to thicken, especially at cooler (below 28^oC) temperatures. If the organism can release gelatinase enzymes the gelatin is broken down or liquefied. The media is checked over a menstruum of about a week after inoculation and incubation at room temperature, for gelatinase activity. The tube is placed on ice for a few minutes and if the media fails to solidify information technology is considered a positive exam. The gelatinase reaction may be slow or incomplete (Fig 7).

Fig 7: Gelatin hydrolysis test (The gelatin hydrolysis is indicated by the liquid nature of the gelatin ( positive test) and the negative examination is indicated by the solid nature of the gelatin)

Nitrate Reduction Broth:

Bacterial species may be classified into different groups depends on their ability to reduce nitrate to nitrite or nitrogenous gases provided in the growth medium. The reduction in nitrate tin exist coupled to anaerobic respiration in some bacterial species. Nitrate, nowadays in the broth, is reduced to nitrite which is and then reduced to nitric oxide, nitrous oxide, or nitrogen. The ground of nitrate reduction test the detection of nitrite and its ability to form a scarlet colored chemical compound when it reacts with reagent A which is sulfanilic acid and to form a complex (nitrite-sulfanilic acid) which then reacts with Reagent B which is α-naphthylamine to requite a scarlet precipitate (prontosil). Zinc powder deed as a catalyst and that will favours the reduction of nitrate to nitrite. Nitrate reaction occurs just nether anaerobic conditions (Fig 8). The medium is then transferred in tubes to make a low area to depth ratio that will limit the diffusion of oxygen into the growth medium. Nearly bacteria utilize the available oxygen in the medium for their growth and volition apace produce anaerobic conditions for the further reactions.

Fig 8: Nitrate reduction exam

Catalase Test:

The inability of strict anaerobes to synthesize catalase, peroxidase, or superoxide dismutase may explicate why oxygen is poisonous to these microorganisms. In the absence of these enzymes, the toxic concentration of H₂O₂ cannot be degraded when these organisms are cultivated in the presence of oxygen. Organisms capable of producing catalase speedily degrade hydrogen peroxide which is a tetramer containing iv polypeptide chains, which are normally 500 amino acids long. It besides contains four porphyrin heme groups(ie., iron groups) that will let the enzyme to react with the hydrogen peroxide.

The enzyme catalase is present in most cytochrome containing aerobic and facultative anaerobic bacteria. Catalase has one of the highest turnover numbers of all enzymes such that 1 molecule of catalase can convert millions of molecules of hydrogen peroxide to water and oxygen in a second.

Catalase product and activity can exist detected by adding the substrate H₂O₂ to an appropriately incubated (18- to 24-hour) tryptic soy agar slant culture. Organisms which produce the enzyme intermission downwards the hydrogen peroxide, and the resulting O₂ production produces bubbles in the reagent drop, indicating a positive exam. Organisms lacking the cytochrome system besides lack the catalase enzyme and are unable to suspension down hydrogen peroxide, into O₂ and water and are catalase negative.

Coagulase Examination:

Coagulases are enzymes that clot blood plasma past a machinery that is similar to normal clotting. The coagulase exam identifies whether an organism produces this exoenzyme. This enzyme clots the plasma component of blood. The merely significant disease-causing bacteria of humans that produce coagulase are Staphylococcus aureus. Thus this enzyme is a good indicator of the pathogenic potential of S. aureus. In the test, the sample is added to rabbit plasma and held at 37° C for a specified period of time. Germination of jell within iv hours is indicated as a positive result and indicative of a virulent Staphylococcus aureus strain. The absence of coagulation later 24 hours of incubation is a negative consequence, indicative of an avirulent strain.

Oxidase Test:

Oxidase examination is an important differential procedure that should be performed on all gram-negative bacteria for their rapid identification. The examination depends on the ability of certain bacteria to produce indophenol blueish from the oxidation of dimethyl-p-phenylenediamine and α-naphthol. This method uses N,N-dimethyl-p-phenylenediamine oxalate in which all Staphylococci were oxidase negative. In presence of the enzyme cytochrome oxidase (gram-negative bacteria) the N,N-dimethyl-p-phenylenediamine oxalate and α-naphthol react to indophenol blue. Pseudomonas aeruginosa is an oxidase positive organism.

Starch Hydrolysis Test:

Amylases are a class of enzymes that are capable of digesting these glycosidic linkages establish in starches. Amylases tin can be derived from a diverseness of sources. Amylases are nowadays in all living organisms, just the enzymes vary in activity, specificity and requirements from species to species and even from tissue to tissue in the same organism. Alpha-amylase (1,iv alpha D-Glucan-glucanohydrolase) acts upon large polymers of starch at internal bonds and cleaves them to brusk glucose polymers. Blastoff-amylase catalyzes the hydrolysis of internal Blastoff-1-4 glucan bonds in polysaccharides containing three or more alpha 1-four linkages; it results in a mixture of maltose and glucose. Amyloglucosidase works on the shorter polymers and splits off single glucose sugars. Bacterial alpha-amylase is particularly suited for industrial usage since it is cheap and isothermally stable.
Starch agar is an instance of differential medium which tests the ability of an organism to produce certain blastoff-amylase and oligo-1, vi-glucosidase that hydrolyze starch. Starch molecules are too large to enter into the bacterial cells, so some bacteria volition secrete exoenzymes that will degrade starch into subunits that can be so hands utilized by the organism.
Starch agar is a simple nutritive medium with starch added. Since no colour change occurs in the medium when organisms hydrolyze starch, iodine solution is added to the plate after incubation. Iodine turns bluish, purple, or black (the colour depends on the concentration of the iodine used) in the presence of starch. A immigration around the bacterial growth shows that the organism has hydrolyzed starch.

Lipid Hydrolysis:

Trybutyrene agar is used for the detection and enumeration of lipolytic microorganisms in nutrient and other material (Fig 9).

Fig nine: Lipid hydrolysis: Left side;positive for lipid hydrolysis;right side;negative for lipid hydrolysis

Growth on selective and differential media:

Selective media allows simply the growth of certain types of organisms, while inhibiting the growth of other organisms.

Eg: Mannitol salt agar, Hektoen enteric agar (HE), Phenylethyl alcohol agar.

Differential media are employed to differentiate sure closely related organisms or groups of organisms. Depending on the presence of specific dyes or chemicals in the growth media, the organisms will tend to produce certain specific characteristic changes or growth patterns that can exist used for further identification or differentiation steps.

Eg: MacConkey (MCK)agar, Eosin Methylene Blue (EMB) agar .

Enriched media are media that have been supplemented with highly nutritious materials such as blood, serum or yeast excerpt for the purpose of cultivating fastidious organisms.
Eg: Blood agar, Chocolate agar

Mannitol salt agar is both a selective and differential media used for the isolation of pathogenic Staphylococci from mixed cultures.

Eosin methylene bluish agar is both a selective and differential medium used for the detecting and isolating Gram-negative pathogens residing in the intestine.

MacConkey'due south Agar is both a selective & differential media that is selective for Gram negative leaner and tin can differentiate those bacteria that are able to ferment lactose.

Different streptococci produce dissimilar effects on the red claret cells in blood agar. Those that produce incomplete hemolysis and merely fractional destruction of the cells effectually colonies are called blastoff-hemolytic Streptococci. Characteristically, this type of hemolysis is seen as a distinct greening of the agar in the hemolytic zone, and thus this group of Streptococci has as well been referred to as the viridans grouping.

Species whose hemolysins cause complete destruction of red cells in the agar zones surrounding their colonies are said to be beta-hemolytic. When growing on claret agar, beta-hemolytic Streptococci are pocket-size opaque or semi translucent colonies surrounded by articulate zones in a blood-red opaque medium.

Some species of Streptococci practice non produce hemolysins. Therefore, when their colonies grow on claret agar, no modify is seen in the red blood cells around them. These species are referred to as nonhemolytic or gamma hemolytic Streptococci.

Notation:

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Source: https://vlab.amrita.edu/?sub=3&brch=76&sim=1109&cnt=1

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