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Labs 48-49 & 52
| Question | Answer |
|---|---|
| Enteric family | Large diverse group of gram-negative, facultatively anaerobic rods (Enterobacteriaceae) |
| Coliforms | lactose fermenters; gram-neg, rod shaped |
| MacConkey agar | selective in that bile salts are inhibitory to gram-positive organisms and allow the medium to selectively culture gram-negative organisms |
| Triple sugar Iron (TSI) | differential screening media that can be used to further characterize organisms |
| Question #2: Differentiate a coliform, an enteric that is not a coliform, and enterococci. Give an example of an organism in each group. | Enterics are gram- facultatively anaerobic rods; Coliforms are enterics that produce acid and gas from lactose; Enterococci are catalase-, gram+ cocci belonging to Lancefield Grp D found in GI tract |
| Question #3: Is MacConkey agar a selective medium? A differential medium? How can you tell? | Yes Yes It selects for gram- bacteria & differentiates lactose fermenters from nonfermenters |
| Question #4: Is PEA-blood agar a selective medium? A differential medium? How can you tell? | Yes Yes It selects from gram+ bacteria; bacteria can be distinguished on the basis of hemolysis |
| C.T. #3: You are called to investigate an outbreak of diarrheal disease in a child-care ctr. Symptoms include vomiting,fever,nausea,cramps. You culture feces of kids and find a gram-,lactose- rod. Bacterium does not produce gas from glucose, | makes colorless colonies on MacConkey agar. Use appendix H to identify the genus of this bacterium. (Shigella sp) |
| Sexually transmitted infections (STIs) | most infections of the genital system transmitted by sexual activity |
| Pyocyanin (blue pus) | extracellular water-soluble pigment |
| Question #2: The enterics and pseudomonads look alike microscopically. How can you easily distinguish these two froups of bacteria? | ENTERICS: Glucose Fermentator + Oxidase - PSEUDOMONADS: Glucose Ferm. - Oxidase + |
| Question #3: Why are females more prone to urinary tract infections than males? | Proximity of anus to urethra, short length of uretha and chgs. in normal microbiota b/c of birth control pills, douching, etc... |
| C.T. #2: What role does antibiotic treatment have in yeast infections of the urinary tract? | Antibiotics can eliminate or suppress normal microbiota allowing endogenous yeast to grow with little or no bacterial competition |
| C.T. #3: A healthy 22 y/o woman was seen at a emergency room b/c of frequent/painful urination. Urine culture reveals a gram-, lactose+ rod that produces indole but no H2S. | Escherichia |
| Indicator organisms | used to detect fecal contamination of water |
| Coliforms | aerobic or facultatively anaerobic, gram-, non-endospore-forming,rods that ferment lactose with acid and gas formation within 48 hrs at 35C |
| Fecal coliforms | coliforms from feces |
| Multiple-tube techinique | coliforms are detected in two stages |
| Presumptive test | dilutions from a water sample are added to lactose fermentation tubes;broth can be made selective for gram- bact. by adding lauryl sulfate or billiant green and bile. |
| Confirmed test | done on MUG agar |
| Most probable number (MPN) | is the number of coliforms determined by a statistical estimation |
| Question #2: Why are coliforms used as indicator organisms if they are not usually pathogens? | The presence of coliforms indicates fecal contamination and potential for the presence of pathogens |
| 45Q1:Why is mannitol salt agar used as a selective medium for normal skin microbiota? | It is selective for salt tolerant organisms(up to 7.5%salt). Salt tolerance is a characteristic of organisms found on skin. |
| 45Q2: List 3 identifying characteristics of Staphylococcus aureus. | Clusters, Gram positive cocci, catalase positive, mannitol fermenting, tolerates 7.5%NaCl, and coagulase positive. |
| 45Q3: List 3 factors that protect the skin from infection. | Dry layers of keratin containing cells, sebum(oil), salts, and pH. |
| 45CT1: What is coagulase? How is it related to pathogenicity? | An enzyme that clots the fibrin in blood; coagulase positive bacteria are able to sequester themselves within a clot to prevent host defenses from killing them. |
| 45CT2:Assume that you isolated S.aureus from your skin. How would you determine whether it is penicillin resistant? | Use the disk-diffusion technique or attempt to grow the bacteria in nutrient broth containing penicillin. |
| 45CT3:Bacterial cultures of blood and fluid were taken and were positive for a gram positive, catalase positive,coagulase positive cocci that ferment mannitol. What is this based on the dichotomous key? | Staphylococcus aureus |
| 46 Q1:Is blood agar selective or differential? Explain. | Differential; Bacteria can be distinguished on the basis of hemolysis. |
| 46Q2:Is the Gram stain of significant importance in identifying the organisms studied in this exercise? Explain. | The Gram stain can separate organisms into 2 broad categories, gram neg and Gram pos, but it is of little importance in identification.Test such as the example in question 2 are more useful in identifying a genus or species. |
| 46Q3: You have isolated a Gram positive cocci from a throat culture that you cannot identify as Staphylococci or streptococci. A test for one enzyme can be used to distinguish these bacteria quickly. What is the enzyme? | Catalase |
| Coagulase | an enzyme that coagulates (clots) the fibrin in blood. |
| Upper respiratory tract | Consists of the nose and throat. |
| Lower respiratory tract | Consists of the larynx, trachea, bronchial tubes,and alveoli. |
| (Microbial) Antagonism | Certain microbes of the normal microbiota suppress the growth of other microorganisms through competition for nutrients and production of inhibitory substances. |
| Beta-hemolysis | Complete hemolysis, giving a clear zone with a clean edge around the colony. |
| Alpha-hemolysis | Green, cloudy zone around the colony. Partial destruction of red blood cells due to bacteria-produced hydrogen peroxide. |
| Gamma-hemolysis | No hemolysis, and no change in the blood agar around the colony. |
| Yeasts | nonfilamentous, unicellular fungi that are typically oval or spherical in shape |
| Pseudohypha | A short chain of cells that form when yeasts reproduce and the bud fails to detach itself. |
| Hypha | The name of each strand in the mycelia. |
| Vegetative hyphae | Growing in or on the surface of the growth medium. |
| Reproductive hyphae | Aerial hyphae which originate from the vegetative hyphae and produce a variety of asexual reproductive spores. |
| Septum | The hyphal strands of most molds is composed of individual cells separated by a cross wall(Septum) |
| Septate Hyphae | Septate hyphae are composed of individual cells separated from one another by cell walls. |
| Coenocytic hyphae | Hyphae that lack septa and are a continuous mass of cytoplasm with multiple nuclei. |
| Saprophyte | Obtains it nutrients from dead, organic matter; in healthy animals and plants , they do not usually cause disease.(Zygomycota Phylum) |
| Pathogens | Causing disease in plants and animals. |
| Sabouraud agar | Selective medium, commonly used to culture fungi. It has very simple nutrients (glucose and peptone) and a low pH, whihc inhibits the growth of many other organisms. |
| 33 C2: Compare and contrast yeast and bacteria regarding their appearance both on solid media and other the microscope. | On solid media, yeasts are shiny, and molds are fuzzy due to their hyphae. |
| 33Q2: Define the term yeast. | Nonfilamentous, unicellular fungi that are typically spherical or oval in shape. |
| 33Q4: Why do other media used to culture fungi contain sugars? | Because it inhibits the growth of most other organisms. |
| 33Q6:How do mold spores differ from bacterial endospores? | Bacterial endospores are prokaryotic and mold spores are eukaryotic. |
| 33Q7: Why are antibiotics frequently added to Sabouraud agar for isolation of fungi from clinical samples? | So bacteria do not contaminate the fungi culture. |
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