Basu lab practical 3 – Flashcards
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| Throat culture medium |
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| Sheep blood agar plate |
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| Approximately how many people are healthy carriers of Staphylococcus aureus? |
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| 30% |
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| How is Staphylococcus aureus transmitted? |
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| person to person |
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| Nasal culture medium |
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| Mannitol salt agar plate |
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| Mannitol salt agar medium is selective for? |
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| isolation of staphylococci |
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| Significant ingredients of Mannitol salt agar? |
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| 7.5% sodium chloride mannitol pH indicator phenol red |
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| Why is mannitol salt agar medium selective for staphylococci? |
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| Most microorganisms are inhibited by high salt. Staphylococci can tolerate such concentrations |
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| If mannitol is fermented |
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| the medium turns yellow |
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| Differential properties of Mannitol salt agar? |
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| sugar mannitol as test substrate pH indicator phenol red |
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| If mannitol is not fermented |
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| the medium remains red |
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| What effect does Staphylococcus aureus have on mannitol salt agar? |
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| Ferments mannitol and the medium turns yellow |
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| What effect does Staphylococcus epidermidis have on mannitol salt agar? |
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| Does not ferment mannitol, medium remains red |
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| what is this?[image] |
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Alpha hemolysis/partial hemolysis blood agar medium streptococci |
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what is this? [image] |
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Beta hemolysis/ full hemolysis blood agar plate Streptococci |
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| what is this?[image] |
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Gamma hemolysis/ no hemolysis Blood agar plate Streptococci |
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| A convenient way to classify streptococci? |
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| Based on their hemolytic action |
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| Alpha hemolysis is accompanied by? |
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| Green color around colonies |
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| Another method of classifying Streptococci? |
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| based on antigenic characteristics |
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| How did lancefield name serological groups of streptococci? |
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| Alphabetically A - O |
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| Beta hemolytic streptococci of Lancefield group A |
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| cause 90% of acute streptococcal infections in humans |
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| Lancefield group A beta hemolytic streptococci can be differentiated from other groups by? |
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| Suceptability to bacitracin. |
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| Bacitracin test |
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| Paper filter with bacitracin is dropped onto a freshly seeded culture plate |
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| Two genera of bacteria within gram positive cocci? |
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| Staphylococcus and Streptococcus |
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| Staphylococci produce |
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| catalase |
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| Catalase breaks down |
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| hydrogen peroxide to form water and oxygen |
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| Streptococci do not produce |
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| Catalase |
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| Differentiate between Staph and Strep by |
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| characteristic arrangements in gram stain catalase production |
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| what is this?[image] |
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| Gram positive Staphylococcus |
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| what is this?[image] |
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| Gram positive Streptococcus |
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what is this? [image] |
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| Catalase test |
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| What is on the left?[image] |
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Positive Staphylococcus |
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| what is on the right?[image] |
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Negative Streptococcus |
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| Areas that should normally be sterile? |
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| Larynx, trachea, bronchi, bronchioles, alveoli |
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| what organisms are likely found in the throat? |
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| pneumococci, meningococci or Haemophilus influenzae |
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| which organism is not classified in the lancefield grouping system? |
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| Alpha hemolytic Streptococcus pneumoniae (pneumococcus) |
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| Streptococcus veridians are |
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| part of normal flora, NOT pneumococci |
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| to distinguish Streptococcus veridians from pathogenic Streptococcus pneumoniae |
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| Optochin susceptibility test |
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| optochin is |
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| a chemical that inhibits Streptococcus pneumoniae no effect on veridians (normal flora) |
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| Optochin test uses |
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| Filter paper disk susceptibility |
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what is this? [image] |
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| Bacitracin suceptibility test |
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What is on the left? [image] |
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Group A beta hemolytic Streptococcus pneumoniae Sensitive |
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What is on the right? [image] |
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Non-group A Beta hemolytic Streptococcus viridans Resistant |
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| what is this?[image] |
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Pneumococcal pneumoniae blood smear |
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| [image] |
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Pneumococcal pneumoniae Sputum smear |
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| Staphylococcus aureus criteria |
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| golden pigment beta hemolysin ferments sugar mannitol produces enzyme coagulase |
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| Staphylococcus epideridis |
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| NO golden pigment NO beta hemolysin NO fermenting of sugar mannitol NO production of enzyme coagulase |
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| Staphylococcus aureus on MSA plate |
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| yellow |
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| Staphylococcus epidermidis on MSA plate |
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| pink/no change |
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| what is this?[image] |
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| coagulase test |
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| what is on top?[image] |
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Positive/ no movement Staphylococcus aureus |
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| what is on bottom?[image] |
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Negative/liquid Staphylococcus epidermidis |
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| Explain how Sodium chloride is selective for Mannitol Salt Agar |
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| High salt concentrations inhibit growth of most organisms, Staphylococcus can tolerate it. |
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| Explain how Mannitol is differential for MSA |
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| Staphylococcus aureus ferments the sugar mannitol. |
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| Explain how pH indicator phenol red is differential for MSA |
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| When Staphylococcus aureus ferments the sugar mannitol, it creates an acid byproduct, turning the color to yellow |
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| Upon examination of a gram stained smear, you see gram positive cocci. You are not sure whether they are streptococci or staphylococci. Name an enzyme test that will help distinguish between the two genera |
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| Catalase test |
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| Name the substrate, enzyme, and end-products used to differentiate staphylococcus and streptococcus |
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| 3% hydrogen peroxide Catalase Water and oxygen |
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| You isolated a species of Staphylococcus from a patients specimen. List four criteria you could use to identify the species |
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| Beta hemolysis Coagulase production Golden pigment Mannitol fermentation |
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| A gram positive ciccus that grows in chains in broth medium and produces beta hemolysis on blood agar most likely belongs to which genus? |
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| Streptococcus |
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| To identify the Lancefield group streptococcus belongs to, a disk susceptibility test is performed. Name the test. |
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| Bacitracin suceptibility test |
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| Explain the rationale behind the Bacitracin suceptibility test |
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| Group A beta hemolytic growth is inhibited by bacitracin. Non-group A beta hemolytic is not. |
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| A direct smear of a sputum specimen reveals gram-positive diplococci, many white blood cells, and mucus. You suspect the patient has... |
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| Streptococcus pneumoniae |
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| To confirm diagnosis of Streptococcus pneumoniae, a disk test can be performed, name the chemical in the test. |
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| Optochin |
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| Explain the rationale of the Optochin test |
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| Optochin inhibits growth of Streptococcus pneumoniae, not Streptococcus veridians |
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| Identify the organism: Gram positive coccus, grape-like clusters, beta hemolytic on blood agar medium, ferments mannitol, produces coagulase |
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| Staphylococcus aureus |
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| Identify the organism: gram positive coccus, singles, pairs, and chains, beta hemolytic on blood agar medium, susceptible to bacitracin |
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| Group A beta hemolytic Streptococcus |
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| Identify the organism: Gram positive diplococcus, alpha hemolytic on blood agar medium, susceptible to optochin |
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| Streptococcus pneumoniae |
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| Identify the organism: Gram positive cocci, nonhemmolytic on blood agar medium, produce the enzyme catalase, does not ferment mannitol, does not produce coagulase |
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| Staphylococcus epidermidis |
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| Identify the organism: Gram positive cocci, lack the enzyme catalase, beta hemolytic on blood agar medium, resistant to antibiotic bacitracin |
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| Non-group A beta hemolytic streptococcus |
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| Briefly describe what the enteric bacteria are and explain why biochemical tests are usually used to identify these bacteria |
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| Enteric bacteria are a diverse group of bacteria found in the GI considered as normal flora. We use biochemical tests to differentiate physiological differences and metabolism |
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| What medium is used to detect fermentation of several sugars simultaneously? |
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| TSI (Triple Sugar Iron agar) |
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| Name the sugars in TSI agar |
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| glucose, sucrose, lactose |
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| What is the name of the pH indicator in TSI? |
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| Phenol red |
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| What are the acid and alkaline colors in TSI? |
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| Yellow/Acidic no change/Alkaline |
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| In addition to detecting sugar fermentation, what else can be detected using TSI? |
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| Hydrogen sulfide production (blackening) |
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| What is the pH indicator used in Citrate test? |
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| Brothymol blue |
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| What are the acid and alkaline colors in the citrate test? |
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| Blue/ Alkaline Green (yellow)/ Acidic |
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| Explain the principle of the urea agar slant |
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| Alkalinization/production of ammonia changes color to pink/red |
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| explain the principle of the motility test medium |
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| Stab medium, if it shows diffuse growth from stab line, its positive |
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| Interpret the results: TSI slant: red slant/yellow deep, no bubbles or cracks |
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| Only one suger (glucose) fermented |
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| Interpret the reults: Citrate slant: growth and blue |
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| Alkaline and positive for citrate utilization |
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| Interpret the results: Urea slant: flesh color |
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| No production of ammonia |
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| Interpret the results: Motility deep: diffuse growth from stab line |
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| Positive for motility |
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| What are two ways whereby microorganisms gain entry to the urinary tract? |
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| Normal flora ascend to bladder Bacteria filtered through kidneys descends to urethra |
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| List 4 methods of obtaining urine specimens for culture, which is most common? |
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| Clean, midstream voided specimen (most common) Suprapubic aspiration Cystoscopy Aseptic catheterization |
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| How many colony forming units per ml of urine are there if 150 colonies are counted on a plate innoculated with 0.001 ml of urine? |
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| 150,000 CFU/ml |
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| Why is any bacterial count obtained from suprapubic aspiration significant? |
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| Because it is supposed to be contaminant free, should not have any colonies |
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| If a urine specimen is left at room temperature for several hours before plating out the specimen, how might this affect the results? |
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| Organisms might keep multiplying, skewing the results |
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| What ingredients make MacConkey agar selective for gram negative bacteria? |
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| crystal violet and bile salts inhibit growth of gram positive bacteria |
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| What ingredients make macConkey agar differential for lactose fermentation? |
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| Lactose and pH indicator neutral red |
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| Name a common causative agent of UTI that is gram negative and ferments the sugar lactose |
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| Escherichia coli |
