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Study Guide for MCB 2010C Lab Practical Final Exam Some of these slides were graciously provided by Dr. Gessner Ex. 5-2: Phenol Red Sugar Fermentation Broths • Tube on the left is negative for sugar fermentation (red). • Tube on the right shows the fermentation of a sugar with the production of acid (yellow) and gas (gas bubble in the Durham tube). Ex. 5-17: Indole Production (SIM Agar Deeps) • The tube on the left (yellow) is negative for the production of indole. • The tube on the right (red layer) is positive for the production of indole. Ex. 5-3: Methyl Red Test • The test on the left is negative (yellow). • The test on the right is positive (red) for the production of mixed acids from the fermentation of glucose. Ex. 5-3: Voges-Proskauer Test • The tube on the left is MRVP broth before inoculation. • The tube in the middle is a negative test (dirt or mud color). • The tube on the right is a positive test for neutral end products (wine color). Ex. 5-7: Citrate Utilization • The tube on the left is negative for citrate utilization. • The tube on the right is “prussian blue” and is positive for citrate utilization. Ex. 5-8: Lysine Decarboxylase • Tube on the left is negative for the enzyme (it ferments glucose to produce an acid, but doesn’t have the enzyme lysine decarboxylase). • Tube on the right shows the presence of the enzyme, a positive result. • Tube on the right is the color of uninoculated media also. Ex. 5-15: DNA Hydrolysis on Dnase medium • The streak on the bottom is positive for DNase enzyme • The streak on the top is negative for the DNase enzyme Ex. 5-12: Urea hydrolysis • The tube on the left is negative for the presence of urease. • The tube on the right is positive for the presence of urease. Ex. 5-14 Gelatin Hydrolysis: Some bacteria have enzymes which breakdown the gelatin (which is protein) to amino acids; as indicated by liquefaction in test tube B. Remember: Besides the fact that most bacteria are unable to digest agar, agar is superior to gelatin because it remains solid well above room temperature (~25°C). Whereas gelatin begins to melt around 25°C. Ex. 5-9: phenylalanine deaminase • The tube on the left is positive for the enzyme • The middle tube is uninoculated • The right tube is negative for the enzyme Ex. 5-4: Catalase Production (cont.) • The tube on the left is catalase negative. • The tube on the right has bubbles and is catalase positive. Ex. 5-20 Blood Agar Gamma Hemolysis: No destruction of red blood cells Is blood agar selective, differential or enriched? Photo: Courtesy of Dr. Kaiser, C.C. of Baltimore County Blood Agar Alpha Hemolysis: Partial destruction of red blood cells. Indicated by the greenish coloration of the media around the bacterial growth. Photo: Courtesy of Dr. Kaiser, C.C. of Baltimore County Blood Agar Beta Hemolysis: Complete destruction of red blood cells. Indicated by the clear area around the bacterial growth. Photo: Courtesy of Dr. Kaiser, C.C. of Baltimore County Ex. 5-18: Kligler’s Iron Agar • The tube on the left is uninoculated. • The second tube shows glucose fermentation only (KA--) • The third tube shows gas production (see gap in the bottom of the agar) and the fermentation of lactose and glucose (AA+-) • The fourth tube shows glucose fermentation only, and H2S production (black) (KA-+) Ex. 5-21: Coagulase Test • The tube on top is positive for the presence of the enzyme • Tube on bottom is negative for the presence of the enzyme Ex. 5-6: Nitrate reduction • After addition of reagents A and B: – Pseudomonas aeruginosa: appears negative, no color change: must test further – Escherichia coli: positive, color change to red – Corynebacterium xerosis: appears negative, no color change: must test further Courtesy of Austin Community College Ex. 5-6: Nitrate reduction, Cont. After addition of Reagent C (zinc): Pseudomonas aeruginosa: Positive (no color change) Corynebacterium xerosis: Negative (color change to red) Courtesy of Austin Community College Ex. 5-5: Oxidase test • The streak on the right is positive for the oxidase enzyme • The streak on the left is negative for the oxidase enzyme Ex. 5-10: Bile Esculin Agar (BEA) • Group D Streptococci and Enterococci darken the medium around its growth. Other microbes do not. •Notice the positive result on the bottom streak • The top streak is negative Enterotube Figure 10.9