Micro Last Lab Quiz

Purpose: to determine whether an organism produces urease, an enzyme that hydrolyzes urea into ammonia and carbon dioxide Media: urea broth or urea agar Indicator: phenol red Interpretation of results: the indicator will turn pink within 24 hours if the organism produces urease because the pH will become more alkaline due to ammonia production

Purposes: to determine whether an organism 1. reduces sulfur 2. is motile 3. produces tryptophanse, an enzyme that hydrolyzes the amino acid tryptophan into indole Media: SIM medium Reagent: indole reagent (aka Kovacs' reagent) Interpretation of results: 1. black precipitate is evidence of sulfur reduction 2. growth spreading out from the stab line is evidence of motility 3. red color in the reagent layer is evidence of indole production

Purpose: to determine whether an organism reduces nitrate (in anaerobic respiration), and if it does, what the final product of nitrate reduction is Media: nitrate broth Reagents: nitrate reagents A and B Interpretation of results: if you know that the organism doesn't produce carbon dioxide from the fermentation of carbohydrates, then you can interpret gas in the Durham tube as evidence of denitrification (nitrate reduction to nitrogen gas), red color after reagents are added is evidence of nitrate reduction to nitrite, red color after adding zinc means that nitrate was not reduced by the organism

Organisms that ferment also produce gas. You cannot tell if the gas is from the fermentation or nitrate reduction.

Purpose: to determine whether an organism produces the enzyme catalase (which breaks down hydrogen peroxide (H2O2) into water and oxygen gas) Procedure: hydrogen peroxide is dropped on to bacteria on a slide or growing on an agar plate Interpretation of results: bubbling (due to the production of oxygen gas) is evidence of catalase production

Purpose: to determine whether an organism produces cytochrome oxidase (the final carrier in an electron transport chain that passes electrons to O2 in aerobic respiration). Procedure: oxidase reagent is dropped directly onto bacteria on a cotton swab Interpretation of results: an immediate color change to purple indicates cytochrome oxidase production

Community of microbes that are growing on a moist surface. They can attach to soil particles, pipes, and contact lenses.

- Same/Similar bacteria -Similar environmental conditions.

Environmental factors like location, temperatures, common weather conditions.

Defense against physical forces, phagocytosis, against penetration of chemicals such as antibiotics. Proximity to other bacterial cells.

Microbial competition. Restricted growth within the biofilm.

Bacteria that grow on biofilms grow faster, exchange DNA easier, and are more likely resistant to antibiotics.

Obtain samples from different days throughout the year from the same location. Days must have different temperatures.

Uv radiation kills the bacteria.

The cells were able to repair the damage caused by UV.

UV radiation isnt strong enough to pass through card board.

Long UV exposure reduces/eliminates growth of the Serratia marcescenes. Plates with a mask and no lid exposed to UV for 3 seconds should be compared to plates that were exposed to 30 seconds.

The masked blocked UV radiation tot he plates. Plates incubated in sunlight should be compared to plates incubated in the dark. The areas covered by the mask showed growth, and the areas uncovered had very minimal growth.

The plastic lid affected UV radiation from passing through. Plates with a mask and no lid should be compared to plates with a mask and a lid. The areas that were exposed to the UV light with plastic lid had growth.

Sunscreen successfully protected the Serratia marcescens and the bacteria grew a lot. Very little to no growth appeared to the UV exposed area.

Purpose: Allows differentiation of bacteria based on their ability to hemolyze Red Blood Cells. Media: Sheep Blood Agar

Clearing around growth. Organism hemolyzes RBCs completely (Beta-hemolysis) Greening around growth. Organism hemolyzes RBCs partially. (alpha-hemolysis) No change in the medium. Organism does not hemolyze RBCs. (No hemolysis)

The plates don't have an immune system that fights off the bacteria like the human body. The growth on the plate isn't constantly fought off to protect the human body.

Sugary foods

Fermentation is required, so if it has a slant, oxygen exposure would prevent fermentation.

How much sugar a person has taken before the test. If the person brushed their teeth.

Steptococcus mutans

Purpose: Favor the growth of oral bacteria. Determining an individuals susceptibility to tooth decay. Media: Snyder Agar tubes Indicator: Change in pH. Yellowing as pH decreases due to susceptibility to dental caries.

Gram positive, Rods Non Sporing Fac Anaerobe Ferment lactose producing gas.

Always present when bacteria is present in the water and have directly related populations. They disappear right after pathogens disappear. They can be counted without interference by other bacteria and are harmless to the technician.

Not necessarily, further testing required. This suggest that it might be unsafe.

The water is contaminated with coliforms.

Storage: must be stored in 30-40 degrees