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Microbiology Lab
Final exam study guide
| Question | Answer |
|---|---|
| general lab rules: | no food/drinks, hand washing, disposal |
| gram stain procedure & times: | crystal violet stain for 1 minute, gram iodine for 1 minute, decolorizer for 10-20 seconds, safranin stain for 1 minute |
| methods for manipulating cultured organisms while preventing contamination are called _______. | aseptic techniques |
| why is aseptic technique important? | to develop and maintain pure cultures, techniques for transferring growing organisms from a pure culture to a sterile medium without contaminants are essential |
| examples of aseptic techniques | flaming a wired loop, hand washing, wearing gloves |
| antibiotics are chemical compounds that selectively inhibit or kill microorganisms while causing little or no damage to animal cells | antibiotic susceptibility |
| composed of G(+) cocci, arranged in irregular "grape-like" clusters, important part of body's normal flora on skin, mucosal surfaces, and in the upper respiratory tract, some of the most disease causing organisms | staphylococcus |
| composed of G(+) cocci, arranged in chains, found in normal flora and upper respiratory tract, common in throat | streptococcus |
| importance of transport to urine cultures | urine often becomes contaminated as it passes out of the body, culturing should begin soon after collection before contaminants can multiply and distort results |
| caused by organisms that enter and multiply in the intestine | food infections |
| ingestion of preformed toxins | food intoxications |
| ex: E. coli, salmonella | food infections |
| ex: Staphylococcus aureus | food intoxications |
| actively growing or vegetative stage | trophozoite |
| dormant stage in the life cycle | cyst stage |
| where is S. aureus found at? | normal flora, usually in nostrils |
| where is S. epidermidis found at? | normal flora, skin and mucous membranes |
| what are the different types of hemolysis? | beta, alpha, and gamma |
| no hemolysis; results in NO change in blood agar | gamma hemolysis |
| hemolysins cause partial lysis of red blood cells; result is a green zone around colonies | alpha hemolysis |
| hemolysins cause complete lysis of red blood cells; result is a clear zone around colonies | beta hemolysis |
| why must skin around the wound be disinfected? | wounds can become infected with skin flora and it is important to be able to distinguish between organisms causing infection and normal flora |
| infection where pathogens are limited to a small area of the body (boils, abscenses) | local infection |
| an infection throughout the body (HIV, measles) | systemic infection |
| when a local infection spreads to another site in the body | focal infection |
| one of the most common sexually transmitted diseases | Neisseria gonorrhoeae |
| is neisseria gonorrhoeae gram negative or gram positive? | gram negative |
| neisseria gonorrhoeae is a common cause of what type of cancer? | cervical cancer |
| can neisseria gonorrhoeae live outside the human body? | no; it must be transmitted from one human to another to survive |
| N. gonorrhoeae can infect what? | any of the mucus membranes |
| pasteurization is named after who? | Louis Pasteur |
| relies on heating to reduce the number of organisms present in milk in order to make a safer product | pasteurization |
| today, pasteurization is used more for... | increasing the shelf-life of the product, than for preventing the spread of disease |
| at the time that pasteurization was developed, ______ were prone to infections of the _______ which could be transmitted to humans. | cattle; udder |
| method commonly used by public health facilities | colilert method |
| method rapid to set up and can easily distinguish E. coli from other enterics? | colilert method |
| what color appears when E. coli is present in colilert method? | bright yellow |
| in the colilert method, what does the yellow color indicate? | that lactose fermenters are present |
| in filtration method, the bacteria are grown on what? | eosin methylene blue agar (EMB) |
| is EMB selective or differential? | both |
| why is EMB selective? | it selects for enteric organisms because it contains bile salts |
| why is EMB differential? | it contains sugar lactose |
| in filtration method, colonies that can ferment lactose appear what color? | pink |
| colonies of E. coli have ________ when grown on EMB | a green sheen |
| filtering apparatus to collect the bacteria from 100ml of drinking water | filtration method |
| are yeasts or molds eukaryotes? | both |
| yeasts or molds are single cells? | yeasts |
| yeasts or molds are multicellular filamentous organisms? | molds |
| yeasts grow in a similar manner to ________, producing a creamy colony on agar media | bacteria |
| yeasts or molds grow as large filamentous colonies? | molds |
| is Candida albicans a type of yeast or mold? | yeast |
| are Aspergillus niger and Penicillum notatum yeasts or molds? | molds |
| purpose of crystal violet? | to stain the cell walls of both gram negative and gram positive organisms |
| purpose of gram's iodine? | acts as a mordant and causes crystal violet to form large crystals within the cell wall |
| purpose of decolorizer for gram-positive cells? | disolves crystal violet and dehydrates the thick cell wall of gram-positive cells (makes it hard for stain to leave cell wall so gram-positive stays purple) |
| purpose of decolorizer for gram-negative cells? | dissolves lipid in the outer membrane and washes crystal violet out of the thin peptidoglycan layer; gram-negative bacteria becomes colorless. |
| purpose of safranin? | stains all cells pink, but gram-positive cells remain strong purple color |
| the presence of bacteria in voided urine | bacteriuria |
| if an organism is resistant to an antibiotic that inhibits other flora, the drug can be added to the growth medium to select for the growth of the organism of interest | selective medium |
| contains a substance(s) that if used by the organism causes a visible change in the medium | differential medium |
| good ex. of differential/selective mediums; contains mannitol and pH indicator that changes color when mannitol is fermented and thus acid is produced | mannitol salt agar (MSA) |
| agar that contains substances that inhibit the growth of gram-positive organisms | Eosin Methylene Blue (EMB) |
| an example of a differential media that is not selective | blood agar |
| chemical compounds that selectively inhibit or kill organisms while causing little or no damage to animal cells | antibiotics |
| one of the oldest methods for evaluating the effectiveness of a particular antibiotic against a specific type of bacteria | Kirby- brauer method |
| steps of kirby-brauer method: | mueller-hinton agar is inoculated with pure culture of an organism, filter paper disks w/ antibiotic are placed on agar surface, antibiotic diffuses thru the medium, after incubation the plates are inspected |
| a type of exotoxin | enterotoxins |
| conditions most commonly due to a sudden decrease in the normal intestinal flora following treatment with a broad-spectrum antibiotic | superinfection |
| cavities | dental carriers |
| the amount of oxygen microorganisms use when they metabolize the organic material in water or milk is called | Biological Oxygen Demand (BOD) |
| fungi that display both morphologies depending on environmental conditions | dimorphic fungi |
| causes the illness popularly referred to as the "24 hour flu" | Norwalk virus |
| bacteria in the blood | bacteremia |
| blood poisoning, growth of bacteria in the blood | septicemia |
| enzyme used to distinguish between streptococci and staphylococci | catalase |
| the removal of oxygen can be followed using what? | methylene blue |
| what does CFU mean? | colony forming unit |
Created by:
yulissalira
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