Biochemical Testing in Microbiology PDF

1/3/2025 BIOCHEMICAL TESTING IN MICROIOLOGY Afsheen Aman, Ph.D. Professor KIBGE BTH-414 Department of Biotechnology University...

1/3/2025 BIOCHEMICAL TESTING IN MICROIOLOGY Afsheen Aman, Ph.D. Professor KIBGE BTH-414 Department of Biotechnology University of Karachi 1 Distinguishing Enterobacteriaceae Large family of bacteria Gram negative rods Capable of fermenting various sugars Many found in the intestines of human or other mammals Varrying pathogenicity: Commensals, opportunists or pathogens Some found in the environment Example species: Escherichia coli Proteus mirabilis Klebsiella pneumoniae Salmonella typhi Citrobacter freundii Shigella dysenteriae Enterobacter aerogenes Yersinia enterocolitica 2 1  1/3/2025 Previous Experience with Enterobacteriaceae: EMB Media ◼ Large amounts of acid from lactose fermentation cause the dyes to precipitate on the colony surface, producing a black center or a “green metallic sheen” (E. coli) ◼ Smaller amounts of acid production result in pink coloration of the growth (E. aerogenes) ◼ Nonfermenting enterics do not produce acid so their colonies remain colorless or take on the color of the media (P. vulgaris) 3 Biochemical Testing Triple Sugar Iron (TSI): fermentation of sugars, sulfur reduction IMViC: Indole: Break down the amino acid Tryptophan Methyl Red: Glucose oxidation Voges-Proskauer: Production of neutral end products Citrate: Citrate fermentation Urease: Hydrolyzation of Urea Phenylalanine Deaminase: converts the amino acid phenylalanine to phenylpyruvic acid Nitrate Reductase: Reduction of nitrate (NO3) to nitrite (NO2) 4 2  1/3/2025 TRIPLE SUGAR IRON TEST (TSI) ◼ Used to differentiate among the different groups of Enterobacteriaceae based on their ability to ferment glucose, lactose and/or sucrose ◼ Also differentiates between groups capable of reducing sulfur to hydrogen sulfide (Sodium Thiosulfate -> Hydrogen sulfide) 5 TSI Results: ◼ Red slant/Red butt = no fermentation ◼ Red slant/Yellow butt = only glucose fermentation ◼ Yellow slant/yellow butt = lactose and/or sucrose fermentation Dark color: Hydrogen Sulfide produced Sodium thiosulfate reduced P 190 6 3  1/3/2025 IMViC TESTS ◼ A series of four tests consisting of: Indole: Break down the amino acid Tryptophan Methyl Red: Glucose oxidation Voges-Proskauer: Production of neutral end products Citrate: Citrate fermentation ◼ Used to differentiate the Enterobacteriaceae ◼ We will look at each test individually 7 Indole Test (SIM: Sulfide,Indole,Motility) ◼ Identifies bacteria capable of producing indole ◼ Some bacteria are capable of converting tryptophan (an amino acid) to indole and pyruvic acid by using the enzyme tryptophanase ◼ Pyruvic acid can be converted to energy or used to synthesize other compounds required by the cell Tryptophan Indole Ring Pyruvic Acid Ammonia 8 4  1/3/2025 Procedure: ◼ Obtain 4 SIM Deep tubes ◼ Inoculate by the stab method with the following organisms: E.coli, P.vulgaris, E. aerogenes K. pneumoniae 9 Indole Test Results: ◼If indole is produced, upon addition of Kovac’s Reagent (10 drops), a “cherry-red” band forms on the surface of the media ◼ Motility (if present) can be seen as growth of the bacteria away from the stab line ◼ Sulfur in the media may be reduced to hydrogen sulfide (H2S); this appears as a “blackening” within the media 10 5  1/3/2025 Methyl Red Test ◼ Used to determine the ability of a bacteria to oxidize glucose and produce stable acid end products ◼ Methyl red is a pH indicator (red at pH less than 4.4 and yellow at a pH greater than 6) ◼ The combination medium used for this test is the MR-VP (methyl red/Voges-Proskauer) broth Acid production: positive methyl red End products of neutral pH : positive Voges-Proskauer 11 Procedure: ◼ Obtain 3 MR-VP broth tubes ◼ Inoculate (using a loop) with the following organisms: E.coli K.pneumoniae E.aerogenes 12 6  1/3/2025 Results: ◼ From the 3 MR-VP broths that you inoculated, transfer 2 mLs from each and place into 3 separate clean tubes (set aside these aliquots for the VP test) ◼ To the remaining, original tubes that you inoculated add 5 drops of methyl red indicator ◼ A red color indicates that glucose has been oxidized 13 Methyl Red Test Results: ◼A red color indicates that glucose has been oxidized. ◼ Methyl red positive tube on the right ◼ Methyl red negative tube on the left 14 7  1/3/2025 Voges-Proskauer Test ◼ Used to determine the ability of microbes to produce nonacidic or neutral end products ◼ Remember that the MR-VP broth is a combined medium used for two tests— Methyl Red and Voges-Proskauer ◼ You have already inoculated the 3 MR-VP broth tubes from the previous procedure (Methyl Red Test) with E.coli K.pneumoniae E.aerogenes 15 Voges-Proskauer Procedure: ◼ To the aliquots of each broth culture separated during the methyl red test, add: 10 drops of Barritt’s Reagent A; shake 10 drops of Barritt’s Reagent B; shake Reshake the culture every 3 to 4 min. It can take as long as 15 min. for a color change to occur 16 8  1/3/2025 Voges-Proskauer Results: The presence of a deep rose color after 15 minutes is indicative of non-acidic / Voges-Proskauer neutral metabolic end products and a positive VP test result. ◼ Voges-Proskauer positive on the right ◼ Voges-Proskauer negative on the left 17 Citrate Utilization Test ◼ Used to determine if an organism is capable of fermenting citrate and using that citrate as its sole carbon source ◼ The ability of an organism to utilize citrate occurs via the enzyme citrase 18 9  1/3/2025 Procedure: ◼ Obtain 3 Simmons Citrate agar slants ◼ Inoculate these slants using the stab and streak method (the same way you inoculated the TSI media using a needle) with the following organisms: E.coli K.pneumoniae E.aerogenes 19 Citrate Test Results: ◼ Simmon’s Citrate agar utilizes sodium citrate as its sole carbon source ◼ Bromthymol blue is included as a pH indicator; the medium initially is green ◼ Organisms capable of using citrate as a carbon source turn the media “Prussian blue”. - + - + 20 10  1/3/2025 Summary of IMViC Reactions Page 199 21 Urease Test ◼ Used to differentiate organisms based on their ability to hydrolyze urea with the enzyme urease ◼ The pH indicator, phenol red, is used to detect the breakdown of urea and the production of ammonia which is used by bacteria to produce amino acids and nucleotides 22 11  1/3/2025 Procedure: ◼ Obtain 2 urea broth tubes ◼ Inoculate with the following organisms: E.coli P.vulgaris 23 Urease Test Results: ◼ Urinary tract pathogens from the genus Proteus may be distinguished from other enterics urease ◼ Urea + H2O CO2 + H20 + NH3 ◼ As the alkaline end products build, phenol red turns from yellowish to pink—a positive result 24 12  1/3/2025 Urease Test Results ◼As the alkaline end products build, phenol red turns from yellowish gold to pink—a positive result ◼ Urease positive organism on the right ◼ Urease negative organism on the left 25 Phenylalanine Deaminase Test ◼ Used to identify bacteria possessing the enzyme phenylalanine deaminase ◼ Phenylalanine deaminase converts the amino acid phenylalanine to phenylpyruvic acid + NH3 26 13  1/3/2025 Procedure: ◼ Obtain 2 phenylalanine agar slants ◼ Inoculate (with a loop on the surface) with the following organisms: E.coli P.vulgaris 27 Results ◼ Phenylpyruvic acid produced by some organisms is colorless ◼ After inoculation and incubation, 10% ferric chloride, an oxidizing agent, is added to the surface of the slants ◼ Ferric chloride (FeCl3) reacts with the phenylpyruvic acid (if present) and changes color from yellow to green—a positive result 28 14  1/3/2025 Phenylalanine Deaminase Results: Positive Negative Ferric chloride (FeCl3) reacts with the phenylpyruvic acid (if present) and changes color from yellow to green — a positive result Positive Negative 29 Nitrate Reductase Test ◼ Used to detect the ability of an organism to reduce nitrate (NO3) to nitrite (NO2) or some other nitrogenous compound, such as molecular nitrogen (N3) using the enzyme nitrate reductase Nitrate Reductase Forms red color once NO3- NO2- solutions A and B are added. 30 15  1/3/2025 Procedure: ◼ Obtain 3 Nitrate broth tubes ◼ Inoculate (with a loop) those tubes with the following organisms: E.coli A.faecalis P.aeruginosa 31 Results: (Pay close attention to this test; its one of the hardest test to read) ◼ After inoculation and incubation, the ability of an organism to reduce nitrate to nitrite (or molecular nitrogen) is detected by adding two reagents: Solution A (sulfanilic acid) Solution B (α-naphthylamine) ◼ If a red color appears after addition of solution A and B, this is considered a positive result Nitrate Reductase Forms red color once NO3- NO2- solutions A and B are added. 32 16  1/3/2025 Results continued: ◼ If there is no color change occurs after additions of solutions A & B, two possibilities must be considered: 1) nitrates were not reduced by the organism NO3- NO3- 2) the organism possessed such potent nitrate reductase enzymes that nitrates were reduced beyond nitrites to ammonia or even molecular nitrogen Nitrate Reductase N2 (Nitrogen Gas) NO3- NO2- NH3+ (Ammonia) P 219 33 Results Continued: ◼ Next, solution C (zinc) is added to the tubes that showed no color change after addition of Nitrate A & B ◼ Zinc, a reducing agent, is capable of converting nitrate to nitrite; the development of a red color after addition of Nitrate C means that nitrates were present and reduced by the zinc not the organism; this is a negative result NO3- NO3- ◼ If the addition of zinc does not produce a color change, the nitrates were reduced beyond nitrites to ammonia or nitrogen gas; this is a positive reaction Nitrate Reductase N2 (Nitrogen Gas) NO3- NO2- NH3+ (Ammonia) 34 17  1/3/2025 ◼ Solutions A and B ◼ Solution C has been have been added to added to these tubes these tubes C. xerosis - Reductase Negative NO3- NO3- Unreactive tubes P. aeruginosa Reductase Positive E. coli - Reductase Positive Nitrate Nitrate Reductase Reductase N2 (Nitrogen Gas) NO3- NO2- NO3- NO2- NH3+ (Ammonia) 35 18