Flashcards on Microbiology
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| pure culture |
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| a single organism from one colony (one isolated colony) |
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| mixed culture |
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| two or more organisms |
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| normal flora |
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| the bacterial assemblage of normal components found on the skin or mucosal membranes of the body (nose, throat, intestines, vagina) |
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| pathogen |
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| an organism that can cause a disease |
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| color, shape, size, consistency |
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| List 4 characteristics by which bacterial colonies can be distinguished |
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| to prevent contamination from airborne microbes |
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| Why should a petri dish not be left open for extended periods of time? |
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| each time you rotate the plate and streak w/a sterilized loop, you are dragging less organisms |
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| Why is streaking called "streak dilution"? |
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| (a) it is an enrichment that mimics the human environment, and (b) blood agar differentiates for hemolytic vs. non-hemolytic colonies |
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| List 2 reason blood agar is used for throat cultures: |
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| alpha hemolysis |
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| partial clearing and greening on BAP is called... |
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| beta hemolysis |
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| Total clearing of blood around colony on BAP is called |
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| gamma hemolysis |
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| No hemolysis on BAP is called... |
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| 1)Sample dilutions are made. An aliquot of each dilution is put in a sterile plate. Molten agar is added & mixed colonies are counted after a couple of days. *can calculate # of bacteria/ml* |
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| Describe a pour plate: |
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| not all bacteria will grow in the chosen media, therefore cell #'s may be underestimated |
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| What are the disadvantages of a pour plate? |
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| for quality control in the food industry |
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| What are pour plates primarily used for? |
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| to prevent condensation falling on the colonies |
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| Why are all culture plates stored in an inverted position? |
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| inoculating from an original pure culture into new medium (broth or plate) |
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| Define Subculture. |
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| One needs a pure isolate so that you can identify the organism (the pathogen) & test for antibiotic sensitivity. |
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| Why is it necessary to make pure subcultures of organisms grown from clinical specimens? |
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| shoe, floor, gas handle controls |
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| What type of surfaces produced too many colonies to count? (TNTC) |
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| The O.R., Oncology, maternity, Burn unit, Sterile processing unit, the Wound clinic, and ICU |
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| Where in hospitals must organisms be reduced to a minimum? |
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| to prevent microorganisms in hair from contaminating patients |
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| Why should hair be kept clean and controlled when caring for patients? |
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| Keep hair tied back, wash hands frequently, wear surgical gloves to take specimens |
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| How can those who care for patients avoid spreading microbes among them? |
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| so steam can enter them |
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| Why should empty vessels be laid on their sides when autoclaving? |
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| 15 psi (pounds per square inch) for 15 mins. at 121 C (boiling temp) |
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| What temperature, pressure and time is usually used to autoclave? |
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| Bacillus stearothermophilus |
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| Name the organisms used in ampules or paper test strips used in quality control of autoclaved materials |
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| 1) They produce the most heat resistant spores; and 2) The cells are also more resistant to moist heat than other organisms |
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| Give two reasons why Bacillus stearothermophilus is particularly suitable to be used in QC testing: |
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| near the center |
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| If a load of wrapped operating room equipment is being autoclaved, where should you place the QC strip? |
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| incineration |
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| Method used to sterilize soiled dressings from a surgical wound: |
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| autoclave |
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| Method to be used to sterilize stainless steel surgical instruments: |
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| gas sterilization |
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| Method used to sterilize plastic syringes made by industry to be sold to hospitals: |
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| dry oven (no condensation) |
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| Method used to sterilize lab glassware: |
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| 1) To culture all organisms present (enrichment). 2) To differentiate species by biochemical characteristics. 3) Select certain species. |
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| Describe primary media (battery): |
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| Selects for Gram - cells (species) and differentiates for lactose fermentation |
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| Why is EMB agar selective as well as differential? |
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| Yes. Pathogens grow well in blood because it contains hemoglobin and other blood products. |
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| Is blood agar an enrichment media? Why? |
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| pathogens grow well in blood (mimics human environment) |
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| Why is blood agar useful as a primary isolation medium for clinical specimens? |
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| Black/purple colony with green metallic sheen |
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| Describe the appearance of E. coli on EMB: |
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| Pseudomonas aeruginosa grows pink colonies, meaning it is a non-lactose fermenter) |
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| How does E. coli differ from Pseudomonas aeruginosa on EMB? |
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| MSA (Mannitol Salt Agar); Only Staphylococcus species tolerate high salt concentrations ; it also differentates for S. aureus by yellow coloration (because it ferments mannitol) |
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| What type of media would you use to isolate Staphylococcus aureus from a clinical specimen to get fast results? Why? |
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| beta hemolytic, cream colored |
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| Describe the colony morphology for E. coli on Blood agar: |
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| purple with a green metallic sheen (LF) |
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| Describe the colony morphology for E. coli on EMB: |
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| no growth |
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| Describe the colony morphologyfor E. coli on Mannitol MSA |
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| grey colonies |
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| Describe the colony morphology of E. coli on TSA: |
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| tiny white colonies, no hemolysis |
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| Describe the colony morphology of Staphylococcus epidermidis on blood agar: |
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| small white colonies, medium stays pink |
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| Describe the colony morphology of Staphylococcus epidermidis on MSA: |
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| blue/green soluble pigment; grape like smell |
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| Describe the colony morphology of Pseudomonas aeruginosa on TSA: |
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| beta hemolytic colonies, bluish-green |
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| Describe the colony morphology of Pseudomonas aeruginosa on Blood agar: |
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| pink (or colorless); NLF |
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| Describe the colony morphology of Pseudomonas aeruginosa on EMB: |
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| facultative anaerobe |
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| prefers no air but can grow with oxygen |
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| microaerophilic |
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| grows best at low oxygen concentration |
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| complete lysis of blood cells, clear halo around colony |
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| Define and describe beta hemolysis: |
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| partial blood breakdown, greening around colonies |
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| Define/describe alpha hemolysis |
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| no hemolysis, just growth |
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| define/describe gamma (nonhemolytic) hemolysis: |
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| Bacitracin |
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| The A disc contains what antibiotic? |
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| Streptococcus Group A from Streptococcus Group B |
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| What organism is the A disc used to differentiate? |
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| alpha hemolysis |
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| What type of hemolysis is produced by S. pneumoniae? |
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| it is a facultative anaerobe |
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| Why is a candle jar used to grow Streptococcus pyogenes? |
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| See drawing pg 12 of study guide. |
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| Draw the flow diagrams given in lab to differentiate Staphylococcus from Streptococcus and to speciate Group A (Streptococcus pyogenes), Group B(Streptococcus agalactiae), and Group D (Enterococcus fecaelis). |
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| Beta hemolysis |
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| What type of hemolysis is displayed by Streptococci that are most pathogenic for humans? |
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| Yes. Normal flora compete w/pathogens for nutrients. |
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| Is normal flora of the throat beneficial to the host? Why? |
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| (see page 13 of study guide) |
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| Describe the CAMP test, include a diagram. |
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| Streptococcus agalactiae (Group B) |
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| If an organism forms an arrow, but is bacitracin negative, what can you presume it to be? |
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| Streptococcus pyogenes (Group A) |
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| If an organism is CAMP negative but bacitracin positive, what can you presume the organism to be? |
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| see pg. 13 of study guide |
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| Expain how latex agglutination reaction works. Include a diagram. |
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| Add hydrogen peroxide to a portion of a colony on a glass slide. Bubbles present = catalase + ; No bubbles = catalase - |
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| Describe how to do a catalase test: |
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| catalase + |
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| Catalase test results for Staphylococcus epidermidis? |
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| catalase - |
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| Catalase test results for Streptococcus agalactiae? |
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| Innoculate organism into rabbit plasma. Incubate 35 C for 3 hrs- 48 hrs. Clot = positive; still liquid = negative |
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| Describe how to do a coagulase test |
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See study guide, p. 14 for answer Streptococcus: Gram - cocci in chains; catalase - Staphylococcus:;gram + cocci in cluster catalase + Staph. aureus:;coagulase +; mannitol + (turns yellow) Staph. epidermidis: coagulase -; mannitol - (stays pink) S. saprophyticus:;resistant to low levels of novobiocin |
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| Draw a flow diagram (from supplies sheet) describing how to differentiate Staphylococcus from Streptococcus and how to speciate Staphylococcus aureus from Staph. epidermidis and Staphylococcus saprophyticus. |
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| white colonies, medium goes yellow due to mannitol fermentation (mannitol +) |
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| Describe the appearance of Staphylococcus aureus on Mannitol Salt Agar (MSA): |
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| pink or colorless, no yellow coloration (mannitol -) |
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| Describe the appearance of Staphylococcus epidermidis on Mannitol Salt Agar (MSA): |
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1) Hemolysins (destroy red blood cells) 2) Leukocidin (destroys leukocytes) 3)Coagulase (clots blood plasma) 4) Staphylokinase (dissolves fibrin clots 5) Enterotoxin (causes gastroenteritis) 6) Hyaluronidase (breaks down connective tissue, producing cellulitis - 'spreading factor') 7) TSST-1 = toxic shock syndrome |
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| Name and briefly describe 7 types of toxins produced by Staphylococcus aureus: |
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Staph. aureus: coagulase +, MSA+ S. epidermidis: coagulase - , MSA - (sensitive to novobiacin) Staphylococcus saprophyticus: coagulase -, MSA -, Novobiocin resistant |
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| How are Staph. aureus and S. epidermidis differentiated from Staphylococcus saprophyticus? |
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| yes |
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| Is Staphylococcus aureus normal flora for some individuals? |
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| Some hospital workers may be carriers. They are therefore a potential health risk to patients. |
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| Of what significance is S. aureus being normal flora for some individuals to hospital staff & their patients? |
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| Chocolate agar |
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| Enriched - 1% hemoglobin and supplements. Isolates most fastidious pathogens such as Neisseria and Haemophilus. |
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| Blood agar plates (BAP) |
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| Enriched and differential - 5% sheep blood; Isolates almost all bacteria; differential for hemolytic organisms. |
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| Mannitol salt agar (MSA) |
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| Selective and differential - 7.5% NaCl and mannitol for isolation ; identification of most S. aureus strains. Isolates Staphylococci and micrococci. |
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| Eosin methylene blue agar (EMB) |
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| Selective and differential - lactose, eosin Y, and methylene blue. Isolates enteric gram-negative bacilli. |
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| Modified Thayer-Martin agar (MTM) |
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| Selective - Hemoglobin, growth factors, and antimicrobial agents. Isolates pathogenic Neisseria species. |
