Lab Ex.’s 45,46,48,49,52

Question Answer
Coagulase An enzyme that coagulates (clots) the fibrin in blood, is pathogenic.
What test is used to test for the presence of coagulase, to distinguish S. aureus from other species of Staphylococcus? Coagulase test
What agar is used for skin bacteria? A mannitol salt agar is selective for salt-tolerant organisms and is differential in that mannitol fermenting organisms wil produce acid, turning the indicator in the media yellow. Most bacteria on the skin are gram (+) and salt-tolerant.
What are 3 identifying characteristics of Staphylococcus aureus?
What are three factors that protect the skin from infection?
The upper respiratory tract consists of? The nose, and throat
The lower respiratory consists of? The larynx, trachea, bronchial tubes, and alveoli.
what is Antagonism? 1.) When two drugs are less effective than either one alone. 2.) competition among microbes for nutrients and production of inhibitory substances.
What is beta-hemolysis Complete hemolysis, giving a clear zone with a clean edge.
What is alpha-hemolysis? Green, cloudy zone around the colony. Partial destruction of red blood cells due to bacteria-produced hydrogen peroxide.
What is gamma-hemolysis? No hemolysis, and no change in blood agar around the colony.
What hemolysis occurs with Streptococci? Alpha-hemolytic and gamma hemolytic are ususally normal microbiota, whereas beta-hemolytic are frequently pathogens.
Is blood agar selective of differential? Selective. It's made with defibrinated sheep blood (5.0%), sodium chloride (0.5%) to minimize spontaneous hemolysis, and nutrient agar. Hemolytic reactions are based on hemolysins that are produced by streptococci while growing on blood-enriched agar.
You have isolated a gram (+) 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? Hemolysis test, to test for hemolysin that are produced by streptococci while growing on blood-enriched agar.
a 45 year old man was admitted to hospital w/ chest pain. A chest x-ray film shows loxer left lung infiltrates. Sutum culture reveals alpha-hemolytic, gram (+), catalase-negative cocci that were inhibited by optochin. What is it? Steptococcus pnemoniae
What is the enteric family? There gram negative, facultatively anaerobic rods and are part of Enterobacteriacea faimly.
Coliforms Aerobic or facultatively anaerobic, gram (-), non-endospor forming, rod shaped bacteria that ferment lactose with acid and gas formation with n 24 hours at 35 degrees Celsius. (Examples: Salmonella and Shigella)
MacConkey agar Is selective in that bile salts are inhibitory to gram-positive organisms; thus, they allow the medium to selectively culture gram-negative organisms.
When is MacConkey agar differential? Lactose-fermenting organisms (coliforms) give red, opaque colonies, and non-lactose fermenters produce colorless, translucent colonies.
Triple sugar iron (TSI) agar Can be used as a differential screening method after isolation on MacConkey agar. No sugar fermentation stays red. With sugar fermentation the areas fermented will turn yellow and have bubbles if gas is present after 24 hr incubation period.
Enterococi Are gram-positive, catalase-negative cocci. They are members of the normal intestinal microbiota of humans and other animals. Can be isolated on an enriched medium (containing blood) that inhibits the growth of gram-negative bacteria.
An outbreak of diarrheal in a child-care center. Symptoms include vomiting, fever,nausea and cramps. In feces cultures you find gram (-), lactose-negative rod. It does not produce gas from glucose ; makes colorless colonies on MacConkey agar. What is it? Salmonella
Examples of an enterococci? Enterococcus faecalis and E. faecium
Examples of a enteric coliform? Salmonella and Shigella
Examples of an enteric that is not a coliform? E.coli and Proteus vulgaris
Pyocyanin A bluish-green pigment produce by the bacteria Pseudomonas aeruginosa (that diffuses into it's growth medium).
Sexually transmitted infections (STIs) Infections that are transmitted by sexual activities. (There major U.S health problems even though most of the bacterial infections van be readily treated with antibiotics if caught early enough.
Most common reportable communicable disease in the U.S.? Is gonorrhea an STI caused by the gram negative diplococci Neisseria gonorrhoeae. (
the enterics and pseudomonads look alike microscopicaslly. How can you easily distinguish these two groups of bacteria? Pseudomonas aeruginosa is characterized by a bluish-green pus it produces extracellularly.
Why are females more prone to urinary tract infections than males? A woman's urethra is shorter than a mans and the woman's urethra is in closer proximity to the anus than a males, which makes it easier for bacteria to creep in.
What role does antibiotic treatment have in a yeast infections of the urinary tract? Antibiotics kill bacteria, some of which are bad (pathogens) and some of which are good(normal microbiota). Antibiotics cannot kill yeasts, so sometimes when too many good(normal flora) bacteria die, it causes an imbalance. Causing an overgrowth of others
An otherwise healthy 22-year old woman was seen at a hospital ER because of frequent ; painful urination. A urine culture reveals a gram (-), lactose-positive rod that produces indole but no H2S. What is the genus of this bacteria? Esherichia (E.coli)
What are indicator organisms? A microorganisms, such as coliform, whose presence indicates conditions such as fecal contamination of food or water.
Coliforms Are aerobic or facultatively anaerobic, gram-negative, non-endospore-forming, rod-shaped bacteria that ferment lactose with acid and gas formation within 48 hrs at 35 degrees Celsius. Not usually pathogenic , but can cause opportunistic infections.
What is a fecal coliform test prove? Appearance of coliform colonies on differential media incubated at 44.5 degrees Celsius is considered a positive test.
What is a multiple-tube technique? In this method, coliforms are detected in two stages in a presumptive test and a confirmed test.
What happens in the presumptive test stage? Dilutions from water samples are added to lactose fermentation tubes. The lactose broth can be made selective for gram-negative bacteria by adding lauryl sulfate or brilliant green and bile. Fermentation of lactose to gas is a positive reaction.
What happen during the confirmed test stage? Samples from the (+) presumptive tube at the highest dilution are examined for coliforms by inoculating a differential medium. It can be done on MUG agar. (if E.coli is added to a nutrient medium containing MUG, GUD converts MUG to a florescent compound.
Most probable number(MPN) method The most probable number of coliforms per 100 ml of water (A statistical determination of the number of coliforms per 100 ml of water or 100g of food).
Why are coliforms used as an indicator organisms if they are not usually pathogens? There not usually pathogenic bacteria, although they can become opportunistic bacteria. They are the most easy to use to detect a fecal contamination.

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