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2012-04-30 13:03:15
microbiology lab exam

microbiology lab exam #3
Show Answers:

  1. What orginisms are used in the fermentation of food products such as wine, vinegar, buttermilk, and sauerkraut?
    Saccharomyces (yeast), Acetobacter, lactobacillus (bacteria)
  2. What orginism did we use in the production of wine?
    Saccharomyces cervesiae
  3. What substances are produced as a result of saccharomyces cerevesiae fermenting sucrose?
  4. What was the purpose of the balloon?
    attached over the lip of the flask to exclude o2 uptake and trap gases (Co2 which is an acid) that might be produced
  5. What effect did the fermentation have on the pH of the wine? Why is that?
    Fermentation will make the juice more acidic due to the acids added during the fermentation process. However our pH remained the same.
  6. What two orginisms are typically used to produce yogurt?
    Streptococcus thermophilus and lactobacillus bulgaricus
  7. What products of fermentation is responsible for converting milk into yogurt?
    Lactobacilli which are products of fermentation
  8. What changes did you note after the milk was allowed to ferment?
    • Liquidfied--semi-solid mixture
    • Milky aroma--sour-milk aroma
  9. Why cool the milk to 45*C before adding the starter culture?
    because any degree higher would kill the micorbes or inhibit their growth. 45* is the optimal temp.
  10. Destroy or inhibit the growth of other microbes. They are synthesized, secreted by certain bacteria, actinomycetes and fungi.
  11. drugs created in the lab, where the mode of action, possible adverse effects in the host and the scope of its anti-microbe behavior is known
    synthetc drugs
  12. a standardized diffusion procedure (using confetti like filter paper discs) used to determine the drug susceptibility of microbes isolated from infectious processes?
    Kirby-Bauer method
  13. the clear zone surrounding each disc that indicated the presence of growth inhibition
    Zone of inhibition
  14. referes to enhanced bactericidal activity. when the sum of the effects of 2 or more chemotherapeutic agents combined is greater than their effects when used alone?
  15. prevents transpeptidation, produces a weakended peptidogylcan structure
  16. prevents H+ bonding b/w the anticodon and t-RNA amnio acid complex and the codon on the mRNA during protein synthesis?
  17. inhibits RNA synthesis
  18. misreading of codons in mRNA, interfers with protein synthesis
  19. prevents peptide bond formation b/w amino acids during protein sythesis
  20. inhibits cell wall sythesis
  21. destruction of cell membrane
  22. inhibits DNA sythesis
  23. What organisms were more resitant to antibiotics overall?
    B. Cereus
  24. Which organisms were more sensitive to abx overall?
    E. coli
  25. Which antibiotics worked against the most type of bacteria?
    azithromycin, meztocillin
  26. Whcich abx were least effective?
  27. Which types of organisms are more resistant to abx in general?
    gram negative
  28. Germicidal denaturing of proteins, disrupts cell membrane
  29. phenol like, poisoniou-external use only, known as lysol
  30. lipid solvent, denaturing and coagulation of proteins, wetting agent in tincutures
  31. reacts with water to form hypochlorus acids which is bactericidal, germicide from combination with proteins, noncompetitive inhibition of enzymes
  32. mercuric ion results in precpitation of cellular proteins, noncompetitive inhibition of specific enzymes caused by sulfhydryl group SH
    heavy metals
  33. precipitate cellular proteins, interfere with metabolic activity, inorganic salt are germicidal
    silver compounds
  34. lowers surface tension and aids in mechanical removeal of bacteria and soil, interfers or depresses the metabolic activities of microbes, disrupts cell membrane, alters cell permeability
    Surface active agents
  35. alkylating agent causes reduction of enzymes
  36. What is the diffeence in anticeptics and disinfectants?
    what they target, anticeptics are used on living tissue, disinfectants are used on objects
  37. Explain how the effectiveness of antiseptics or disinfectants is altered by concentration, length of exposure, temp, pH and surface materials?
    • concentration-generally higher concentrations produce more rapid death.
    • LOE-varies depending on the microbes in question, typically longer the greater teh antimicrobial acitivity
    • Temp-increased temp=increased rate of chemical reactions which destroys microbes
    • pH-extreme pH are harmful to many microbes and enhance antimicrobe action
    • surface material-if found on blood pus etc-combination will yeild a reduction in the antimicrobe action
  38. Which antimicrobial agent was most effective?
    iodine followed by H2O2 (3% hydrogen peroxide)
  39. Which organisms was most susceptible?
    B. Cereus
  40. which organism was least susceptible to antimicrobial agents?
  41. How can u calculate the CFU/g of a food substance?
    count the number of colonies on plate <30 TFTC, >300 TNTC, mutilply # of colonies by dilution factor.
  42. Do u expect food products to contain microbes? Why?
    yes, food contains microbes because food contain organic nutrients that provide an excellent medium to support the growth and multiplication of microbes.
  43. if foods contain microbes, does that mean that the food is contaminated or unsafe? Why?
    no, some microbes are completely harmless post ingestion, they can be beneficial
  44. Which food substances contained the largest numbers of microbes? Which contained the least?
    • Ground beef (liver) contained the most.
    • dried fruits (raisin) contained the least
  45. Milk is pasteurized prior to sale. does this affect the way you view the numbers of microbes present in the milk sample?
    yes, without psaeurization there wuld be alot more bacteria in milk including harmful coliforms.
  46. Why use EMB?
    emb medium permits the differentation b/w enteric lactose fermenters and nonfermenters as well as ID of the colon bacillus E. Coli with a metallic green sheen
  47. Why are ground meat products likely to contain more enteric bacteria than many other foods sources?
    perfect medium of nutrients for enteric bactera as opposed to the dried fruits which lack the rich ingrediants.
  48. specific test for detection of coliforms, ac bacteria that is capable of using lactose as a carbon source producing acid and gas. gives an idea of the MPN
    Presumptive test
  49. assures that the bacteria found are coliforms. uses selective and differnetial media EMB or Endo, streaked with the positive lactose fermenters. inhibits gram+ organisms and tests mainly for E. coli a positive indicator of feca pollution.
    confirmed test.
  50. What is the MPN
    the most probable number of coliforms present in the water.
  51. How can u determine the MPN of a water sample?
    estimated by determining the number of tubes n each group that shows a gas post incubation
  52. Why use EMB as a confirmed test. What does a + test result look like on EMB?
    b/c of its differential and selective properties. inhibits the growth of gram + bacteria and turns metallic green in the presence of E. coli
  53. What is the role of the Durham tube?
    detects gas formation by collecting gas bubbles.
  54. What media is used fro determining the MPN?
    lactose medium
  55. Which types of water smaples are more likely to be contaminated with enteric bacteria? why?
    sewage water, bogs and swamps. b/c sewage contains feces, and bogs and swamps are stagnat.
  56. What type of bacteria are commonly found in the mouth?
    lactobacillus acidophilus, streptocoocus mutans and actinomyces odontolyticus
  57. What is the function of dextransucrase?
    enzyme secreted by S. Mutans, polymerizes sucrose into a large polymer, dextran and the monosaccharide fructose. clings to teeth and forms plaque.
  58. What is dextran, which oral bacteria produces it?
    a sugar slime that contributes to dental caries, produced by S. Mutans.
  59. When sucrose is broken down into glucose and fructose, what happens to the glucose? what happens to the fructose>
    the form organic acids mainly lactic acid which decalcifies and softedn the enamel causing gingivitis.
  60. What is the pH indicator used in the snyder test?
    bromcresol green
  61. What information does the synder test provide
    measures the amount of acid produces by the action of the lactobacilli on glucose.
  62. common bacteria of the skin?
    staphylococcu, streptococci, entrococci, dipththeroid bacilli, yeast, fungi.
  63. common bacteria of the eye?
    staph, strep, diptheroids,nesseriae
  64. common bacteria of the upper resp. tract?
    staph, strep (s. pneumoniae) enterocooci, diptheroids, spirochestes and moraxella, nessieria, haemophilus
  65. common bacteria of the mouth?
    anaerobic spirochets and vibrios, fusiform bacteria, staph, anaerobic strep.
  66. coomon bacteria of the intestine?
    lactobacilli and enterococci, abcteriodes, lactobacillus, clostridium, streptococcuc, coliforms, enterococci, proteus, pseudomonas and candida
  67. common bacteria of the genitourinatry tract?
    staph, strep, lactobacilli, gram neg bacilli, clostrdia, spirochestes, yeast, and trichamonas
  68. no lysis of RBC+no color change on blood agar
    Gamma hemolysis
  69. incomplete lysis=green speckeled appearance on blood agar, S. Pneumoniae
    alpha hemolysis
  70. lysis of RBC=smooth spreading that is yellow, S. Pyogenes
    beta hemolysis
  71. What organism is grown on chocolate agar? how is it recongnizable?
    Neisseria spp. will turn pink to dark purple with the addition of p-aminodimethylaniline
  72. What is the purpose of the candle jar?
  73. What organism is detected on MSA? how does it appear?
    Pathogenic S. aureus, turns yellow surrounding the growth.
  74. What does a yellow discoloration on MSA mean? what is fermented?
    fementation of mannitol.
  75. What organism grows on Sabouraud agar?
  76. both contain staphylococcus, streptococcus, both have alpha and non-hemolytic properties, entericocco and diptheroids. differnces throat is S. pneumoniae, skin is S. epidermis, skin also yeast and fungi, throat -moraxella and neisseria adn haemophlius.
    throat and skin
  77. What illnesses are associated with staphylococcus aureus?
    abscess, boils, carbuncles, acne, impetigos, pneumonia, osteomyletis, endocarditis, cystitis, pyelonephritis , staphlococcal enteritis and septicemia.
  78. is growth and fermentation on MSA sufficient to ID S. aureus? why or why not?
    yes becaus MSA is selective for salt tolerant orgnaisms and fermentation of mannitol. S. aureus is both
  79. What is the role of coagulase on indentifying pathogenic staphylococci?
    cpnverts fibrogen into fibrin mesh, charateristic of the pathogensic SA.
  80. How can latex bead agglutination be used to ID pathogenic staphylococci?
    uses protein coated latex particles that detects the clumping factor that causes SA to stick to the latex particels, causing agglutination
  81. how are streptococci identified based on hemolysis?
    by the amount of RBC destruction they cause
  82. what are the lancefield groups?
    A,B,C,D out of 20 serogroups
  83. What are the characteristics of Group A strep?
    beta hemolytis that encompesses strep pyogenes, main etiological agents of resp infections. Examples: tonsillitis, bronchopneumonia, scarlet fever, erysipelas, cellulitis.
  84. what are the characteristics of group B strep?
    also beta hemolytic and cause neonatal meningitis, Example: puerperal fever, endocarditis.
  85. what is the importance of optochin and bacitracin in determining which strep pathogen may be present?
    • bacitracin-reveals senstive group A strep that reveal a zone of inhibition
    • optochin-determines the presence of S. pneumoniae which is senstive to the surfactant and reveals a zone of inhibition
  86. What is CAMP test? how is it useful for determining the presence of pathogenic bacteria?
    determines the group B b/c of the peptides they produce.
  87. What are the major characteristics of S. Pneumoniae?
    major alpha hemolytic pathogen, gram + cocco, contains a capsule formed in vivo and they produce an a-hemolysis on blood agar plates.
  88. What illness(es) are associated with S. pneumoniae?
    lobar pneumonia.
  89. positive for soulbility and optochin sensitivty
    S. pneumoniae
  90. negative for bile solubitlity and opthochin senstivity
    S. mitis