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Microbiology Lab Exam

Microbiology Lab Exam . Study Guide by Susan B. Under what circumstances would you give a patient tetanus toxin?. Never!!! It would kill your patient. Tetanus Immunity . Under what circumstances would you give a patient equine tetanus antitoxin?.

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Microbiology Lab Exam

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  1. Microbiology Lab Exam Study Guide by Susan B

  2. Under what circumstances would you give a patient tetanus toxin? Never!!! It would kill your patient. Tetanus Immunity

  3. Under what circumstances would you give a patient equine tetanus antitoxin? Only in emergency situations and only if the patient has had no previous exposure. It can lead to serum sickness, a type III hypersensitivity reaction with fever, arthritis, and acute glomerulonephritis due to the deposition of immune complexes. Tetanus Immunity

  4. Under what circumstances would you give a patient tetanus toxoid? Give to patients with recent exposure to tetanus to induce antibody formation. It should always be given in emergencies along with the antitoxin, injected at a separate site on the body. Toxoid will act within 10-14 days if the patient has no memory cells and within 3-5 days if previously exposed. Tetanus Immunity

  5. Under what circumstances would you give a patient tetanus antitoxin (human)? Always give it when in doubt. It will transiently protect the patient from the fast acting toxin but will not induce active immunity. Tetanus Immunity

  6. What is the basic premise behind Koch’s postulates? You need to be able to isolate a pure culture from an infected host if you are planning on identifying/studying the organism. Koch’s Postulates

  7. What level of magnification can be achieved with an oil immersion lens? X1000, which gives it the necessary magnification to view Gram stains of bacteria. Oil Immersion Microscopy

  8. What is the method of gram staining? Methanol -> Fixes organisms on slide Crystal Violet -> Stains purple Iodine -> Fixes the crystal violet on the peptidoglycan layer Alcohol/acetone -> decolorizes Gram neg bacteria Safranin -> Counterstains gram neg bacteria red Gram Staining

  9. What are the requirements of gram staining? The cultures must be young (12-18 hours) and spread thin to avoid problems decolorizing Gram Staining

  10. How Does Beta Hemolysis appear? Give examples. Clear zone around colony due to total lysis of RBCs GAS (S. Pyogenes), GBS (S. Agalactiae), Staphylococcus Aureus, Listeria Mono. Blood Agar Hemolysis

  11. How Does Alpha Hemolysis appear? Give examples. Green zone around colony due to incomplete lysis of RBCs Streptococcus pneumoniae, Viridans group Streptococcus Blood Agar Hemolysis

  12. How Does Gamma Hemolysis appear? Give examples. No zone around colony due to no lysis of RBCs GDS (Enterococcus, Streptococcus Bovis) Blood Agar Hemolysis

  13. How does the catalase test work and what does it tell you? Hydrogen Peroxide is added to a smear in order to detect the enzyme catalase. This test is used to differentiate between Gram (+) cocci. If bubbles appear, then the test is positive and the gram (+) bacteria must be staphylococcus. Catalase Test

  14. How is acid-fast staining accomplished? What does acid-fast staining indicate? Method: Carbolfuscin/magenta -> primary dye stains pink Alcohol/acid -> washes the dye off everything but AFB Methylene blue -> counterstains everything else Indicates an acid-fast bacilli like mycobacteria tuberculosis Acid-Fast Staining

  15. What does coagulase indicate? No zone around colony due to no lysis of RBCs GDS (Enterococcus, Streptococcus Bovis) Coagulase Testing

  16. Gram Positive Rods? Listeria, Clostridium, Bacillus, Corynebacterium, Mycobacterium, Nocardia Bacteria

  17. Gram Positive Cocci? Staphylococcus Aureus, Coagulase negative Staphylococcus, Group A & B Streptococcus, Streptococcal pneumoniae, Entercoccus Bacteria

  18. Gram Negative Cocci? Neisseria Bacteria

  19. Gram Negative Rods? E. Coli, Klebsiella, Pseudomonas, Proteus, Salmonella, Shigella, Citrobacter, Burkholderia, Yersinia, Enterobacter, Haemophilus, Bordetella, Brucella, Francisella, Citrobacter Bacteria

  20. Why is it important to correctly identify strep throat? 15% of Strep Throat is caused by Streptococcus Pyogenes and if left untreated, may lead to sequelae such as acute glomerulonephritis and acute rheumatic fever (0.5 -3%) Strep Throat

  21. How is strep throat classically diagnosed? Swab Pharyngeal tonsils -> Streak on agar -> incubate for a day. GAS (S. Pyogenes) will show beta- hemolysis. Gram + cocci in chains on gram stain, and reaction with antiserum for group A carbohydrate. Strep Throat

  22. How does the Rapid Strep Test work? It is more specific but less sensitive. Test directly for group A antigen. Swab tonsils -> put on kit and read…. Strep Throat

  23. What constitutes a good specimen? Collected with metal (scalpel, syringe) and has whole fluids and tissues. Specimen Collection

  24. What constitutes a bad specimen? Collected with swabs, not whole tissues Specimen Collection

  25. What are the symptoms? Purulent urethral discharge, dysuria, urethral pruritis and/or rectal or pharyngeal inflammation… Male Urethritis

  26. What should be included in your differential diagnosis? PMN with gram (-) diplococci -> N. Gonorrheae PMN without gram (-) diplococci -> Chlamydia trachtomatis (until proven otherwise) Male Urethritis

  27. What is the most common STD among men and women? Chlamydia. It is the most common cause of non-gonoccal urethritis in men Male Urethritis

  28. What is the treatment for male and female N. Gonorrhea infection? Gonorrhea -> 3GC or cipro Chlamydia -> tetracycline or erythromycin Usually, you treat both (assume they come together), inform partners and contact health department (yeah, right) Male Urethritis

  29. What are the symptoms of cervicitis? What are the risks of having cervicitis? Inflammation with purulent discharge. Both gonorrhea and chlamydia are risk factors for PID which can lead to ectopic pregnancies, and infertility Female Cervicitis

  30. How is cervicitis diagnosed in women? Culture for Neisseria Gonorrhea using selective media and/or tissue cell culture for chlamydia. *A gram stain of cervical exudate will not be helpful in this case because of the normal vaginal flora present. Female Cervicitis

  31. Three major causes of vaginitis? Bacteria, protozoa, or fungus Female Vaginitis

  32. White cottage cheese-like discharge, pH=4.5. Using a KOH prep, you see budding yeast cells w/ pseudohyphae. What is your diagnosis? Candida Albicans. Treat patient with antifungals Female STDs

  33. Frothy, yellow-green discharge with pH>4.5 Trichomonasvaginalis. Treat patient with metronidazole Note: Use wet prep for trichomonas Female STDs

  34. Thin, white-gray, homogenous discharge with pH>4.5and visible “clue” cells Bacterial vaginosis. Treat patient with metronidazole or clindamycin Female STDs

  35. Thin, white-gray, homogenous discharge with pH>4.5and visible “clue” cells Bacterial vaginosis. Treat patient with metronidazole or clindamycin Female STDs

  36. Most common presentation? Prolonged cough, chest pain, hemoptysis, cachexia Tuberculosis

  37. How to diagnosis TB? NAAT, CXR, skin test, sputum culture, acid fast sputum stain (3 consecutive morning collections) Tuberculosis

  38. What are the limitations of the NAAT test? 95% sensitive when given a AFB positive sputum sample and a culture will still have to be done in addition to this for specific identification of the agent. Tuberculosis

  39. What symptoms are associated with Legionnaire’s disease Sudden onset cough, fever, chest pain, Chest X ray shows consolidation Legionella pneumophila

  40. How can you diagnosis Legionnaire’s disease? Urinary Ag test (sensitive and specific), since legionella doesn’t stain well, and flourescent Abs are not very sensitive. Legionella pneumophila

  41. What causes most lab errors? 50% of lab errors are pre-analytical. Laboratory Testing

  42. What can reduce the amount of lab errors? Label the specific source, ptimmuno status, special requests for tests Laboratory Testing

  43. What do neonates have in their intestinal flora? Nothing! It’s sterile GI Flora

  44. How do neonates acquire their GI Flora? From food, environment, and the birth canal (gross…) GI Flora

  45. Where in the GI tract are most of the normal flora found? Lots of flora in lower GI, only a few in upper GI GI Flora

  46. What type of flora predominate the GI tract? Anaerobes They outnumber aerobes x1000 GI Flora

  47. What type of pathological finding are anaerobes primarily responsible? Intra-abdominal abscesses, peritonitis, C. diff pseudo colitis GI Flora

  48. What type of pathological finding are aerobes primarily responsible? UTIs and sepsis GI Flora

  49. Diarrhea, chicken…………… • Bloody diarrhea………………. • Antibiotics, diarrhea………… • Diarrhea, shellfish, DC……. • Hemolytic uremic syndrome • Appendicitis, diarrhea………. • Salmonella, campy • EHEC, STEC • C. Diff • Vibrio • Shigella, EHEC/STEC • Yersinia enterocolitica GI Flora buzzwords…

  50. What are HEA plates useful for recognizing in stool cultures? Both Salmonella and Shigella Only some gram (-) can grow on HEA Differential Plate Diagnosis

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