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Lab practical II
| Question | Answer |
|---|---|
| How can Streptococcus and Staphylococcus be differentiated | using a catalase test |
| Staphylococcus is catalase ____ what | catalase positive |
| Streptococcus is catalase _____ | Catalase negative |
| What is the reaction that occurs during a catalase test | The substrate hydrogen peroxide is broken down by the enzyme catalase into water and oxygen |
| What produces the visible results of a catalase test | bubbles are formed by O2 |
| How is a catalase test performed | hydrogen peroxide is added to a slide and then mixed using an inoculating loop with bacteria |
| What | gram-positive cocci, facultative anaerobes and aerotolerant anaerobes, catalase negative, many are fastidious |
| What is used to differentiate between streptococcus organisms | Growth on MSA, Hemolytic activity, sensitivity to Bacitracin and SXT, and bile esculin metabolism |
| MSA is able to distinguish between what two species | Enterococcus, which is halotolerant and streptococcus which is non-halotolerant |
| capnophile | grows in CO2 rich environment |
| Blood agar is what type of test | differential and enriched medium |
| What molecules break down RBC | Hemolysins |
| Clear color on single streak blood agar | beta hemolysis |
| brown color on single streak blood agar | alpha hemolysis |
| no color change on single streak blood agar | gamma hemolysis |
| How can one tell is there there is resistance or susceptibility to the antibacterial Bacitracin | any zone of inhibition is susceptible and no zone of inhibition is resistant |
| How can one tell is there there is resistance or susceptibility to the antibacterial SXT | zone of inhibition >20mm is S and anything 20 or less is R |
| What type of medium is bile esculin agar slant | selective and differential medium |
| What does bile esculin slant contain | bile, esculin, ferric ammonium citrate, beef extract, and gelatin extract |
| What is the selective component of bile esculin slant | bile salts |
| What are the differential components of bile esculin slant | esculin and ferric ammonium citrate (iron salt) |
| if bacteria is able to grow in bile salt, what is the reaction that may take place that will help differentiate it? | esculin substrate will be broken down by esculinase into esculetin, glucose, and reacts with ferric ions (or iron) forming a black precipitate |
| A positive bile esculin agar test indicated by | 50% or greater black precipitate present |
| staphylococcus are? | gram-positive cocci, facultative anaerobes, catalase positive and halotolerant |
| how are staphylococcus species differentiated | based on mannitol fermentation, DNase activity, and sensitivity to novobiocin |
| which component of MSA medium is used to identify staph species | differential, because all are halotolerant. |
| What is the reaction that takes place is a staph species is able to metabolize mannitol | Mannitol substrate is broken down by mannitol dehydrogenase into pyruvate which can be further converted into acidic products using fermentation enzymes |
| if mannitol fermentation occurs, what indicates this process | the phenol red will indicate a pH change denoted by either decrease in pH (yellow) or increase in pH (pink) |
| DNase is what type of medium | differential |
| What substrate does DNase medium contain? what does it use to detect reactions | DNA and methyl green as a detection dye |
| What reaction takes place if DNA is hydrolyzed | DNA polymers are broken down by DNase produced by bacteria into DNA fragments. |
| What does a positive DNase test look like | halo clearing around streak caused by methyl green |
| Sensitivity to Novobiocin is included in which test | on the staph identification test on the Mueller-Hinton |
| How do you interpret the results of the novobiocin sensitivity test | Zone of inhibition greater than 18mm is susceptible Zone of inhibition 18 mm or less is resistant |
| What does the rapid strep test do | it is a qualitative test that can rapidly detection of group A strep or S. pyogenes |
| What is the procedure for a rapid strep test | throat swab is taken from individual and mixed with reagent A and B, which extracts strep A antigens |
| What are the regions on a rapid strep test strip | test strip and control region, test strip contains antibodies against group A strep antigen |
| What will a positive rapid strep test look like | pink line in test region as Strep A antigens move up through capillary action until they bind with strep a antibodies |
| What does a rapid staph test do | allow for rapid detection of staphylococcus aureus |
| What does S. aureus contain that allows for its detection | coagulase enzyme and protein A that interact with fibrinogen and IgG antibodies |
| What is the procedure for a rapid staph test | test latex particles coated with fibrinogen and IgG antibodies and control latex are mixed with a sample of S, aureus |
| how are the results for a rapid staph test interpreted | agglutination present is positive and no agglutination is negative |
| Gram negative rods are differentiated using what? | Biochemical tests: MAC, TSI, Urease, citrate, nitrate, SIM, MRVP, Lysine |
| MAC stands for what and what does this medium contain | Stands for MacConkey agar and it contains bile salts, neutral red, crystal violet and lactose |
| What are the differential and selective components of MAC plate | selective for gram neg bile salt and crystal violet, differential for lactose fermentation |
| What is the reaction that takes place if a gram neg bacteria can ferment lactose and what are visible results | lactose is broken down to glucose and galactose using secreted enzyme beta galactosidase and then that is broken down by fermentation enzymes into acid products, which will be depicted as pink or diffused pink if strong fermentation |
| How is a MAC test performed | A t isolation is performed using an inoculating loop |
| What does TSI stand for and what does the medium contain? | Triple sugar iron agar slant. contains 0.1% glucose, 1% lactose, and 1%sucrose, thiosulfate, iron salt, and phenol red |
| What does TSI medium do | creates an aerobic and anaerobic environment due to slant and allows for differentiation based on carbohydrate fermentation, H2S production, and gas production |
| In TSI, what does the thiosulfate do? | acts as a substrate for thiosulfate reductase for H2S determination |
| What does iron salts do in a TSI medium | detection component for H2S |
| What is first potentially metabolized in a TSI slant | glucose, then lactose and sucrose, which is why glucose is in low concentration |
| What are the carbohydrate fermentation reactions in a TSI slant | Glucose --> broken down into acid end products by fermentation enzymes Lactose--> broken down into glucose and galactose using beta galactosidase---> and then broken down into acid end products by fermentation enzymes Sucrose--> sucrase breaks down... |
| How was a TSI performed | inoculating loop zig zag on slant and needle stabbed 7 times on deep. |
| what are some examples of results and what they mean | All red= no carbs fermented only proteins ALK ALK red slant, yellow butt = only glucose fermented A, then proteins ALK all yellow, all carbs fermented A A black: H2S present bubbles cracks: CO2 gas produced |
| What reaction takes place for a black precipitate to form in a TSI tube | sodium Thiosulfate , hydrogen, and electron is broken down by thiosulfate reductase into H2S which reacts with iron salts to show black precipitate. overall organisms undergoes anaerobic respiration using sulfate ions as final e- acceptor |
| What reaction takes place for gas production in TSI tube | carbohydrates are reduced to acid products plus CO2 and H2 which form the cracks and bubbles |
| What does a urease medium contain and what does it do? | it is a broth medium that contains urea and phenol red. test organisms ability to hydrolyze urea into ammonia and carbon dioxide |
| What is the reaction that takes place | urea and water is hydrolyzed by urease (if pathogen contains it) and it is reduced to carbon dioxide and ammonia, which raises the pH and results in a hot pink color |
| What does SIM do and what does it contain? | It contains amino acid tryptophan, sodium thiosulfate, and iron salt. it detects h2s production, motility, and indole production |
| what reagent is used in SIM and what are the result if positive | Kovac after incubation turns cherry red if indole present on top, motility is seen by diffuse growth h2s is seen by black precipitate |
| What reactions take place if indole and H2S are present | tryptophan is broken down by tryptophanase into indole and reacts with kovac, sodium thiosulfate is broken down by sodium thiosulfate reductase into H2S and reacts with iron salts |
| MRVP stands for? contains? does? | Methyl Red v p, contains glucose, phosphate buffer. test if acid end products were produced from glucose fermentation |
| What two tests are performed | Methyl red and Voges-Proskauer |
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Acrob89
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