Lab Quiz 2

• an air dried smear of the organisms is passed held in front of the opening of a microincinerator for 10 seconds
• the heat coagulates the organisms' proteins causing the bacteria to stick to the slide

• an air-dried smear of the organism is covered with a few drops of 95% methanol
• after 2 min the methanol is washed off and the slide is left to air dry
• this causes less damage and distortion to the bacteria

• the color portion of the dye resides in the negative ion
• ex. nigrosin, congo red

• the color portion of the dye resides in the positive ion
• ex. methylene blue, crystal violet, safranin

the color stains the organism directly

the color forms a deposit around the organism, leaving the organism colorless

when using a basic dye, the positively charged color portion of the stain combines with the neg. charged bacterial cytoplasm and the organism becomes directly stained

when using an acidic dye, the color portion of the dye is on the negative ion, so it will not readily combine with neg. charged bacterial cytoplasm and it forms a deposit around the organism, leaving the organism itself colorless

because it differentiates between gram-positive and gram-negative bacteria

• positive - thick, dense wall 20-80nm thick, various layers of peptidoglycan, interwoven w teichoic acids
• negative - only 2-3 layers of peptidoglycan, surrounded by an outer membrane + LPS

in gram-neg, the single thin layer of peptidoglycan is unable to retain the dye bc the outer and inner membranes get dissolved but in gram-positive it can retain the larger molecule complex

• method & technique used - overheating during fixation or over decolorizing or using too much water in washes
• ages of the culture - over 24 hrs old cannot retain crystal violet-iodine complex as well
• the organism itself - some are better at retaining than others

• a slimy, viscous covering
• help bacteria resist phagocytosis
• in soil/water, prevent bacteria from being engulfed by protozoans
• help bacteria adhere to surfaces & resist flushing

• Bacillus
• Clostridium

serves as resistant, dominant survival form of the organism

single flagellum at one pole

two or more flagella at one or both poles

single flagella at both poles

completely surrounded by flagella

internal flagella, usually in spirochetes

the organelles of locomotion

• direct observation of motility using special-purpose microscopes (phase-contrast microscopy vs dark-field microscopy)
• motility test medium (nonmotile - growth only along line of inoculation, motile - growth throughout the tube, cloudy-like)
• flagella staining - used indirectly to denote motility

speed of chemical reactions without being consumed

enzymes located within the bacterium

secreted by bacteria into the surrounding environment in order to break down larger nutrient molecules so they can enter the bacterium

When iodine is added to starch, the iodine-starch complex that forms gives a characteristic dark brown or deep purple color reaction. If the starch has been hydrolyzed into glucose molecules by the diastase exoenzyme, it no longer gives this reaction.

• clear zone surrounds bacterial growth - starch is hydrolyzed
• agar turns dark brown/blue - starch is not hydrolyzed

The protein casein exists as a colloidal suspension in milk and gives milk its characteristic white, opaque appearance. If the casein in the milk is hydrolyzed into peptides and amino acids, it will lose its opaqueness.

• clear zone around bacterial growth - casein is hydrolyzed
• skim milk agar is still white/opaque - casein is not hydrolyzed

• acid end products
• acid & gas end products

• carbohydrate fermentation
• acid and gas products

• carbohydrate fermentation
• acid but no gas products

• no carbohydrate fermentation
• no acid or gas

tryptophan --> indole + pyruvic acid + ammonia

identification of E. coli

• To test for hydrogen sulfide production, a medium with a sulfur-containing compound and iron salts is inoculated and incubated
• If the sulfur is reduced and hydrogen sulfide is produced, it will combine with the iron salt to form a visible black ferric sulfide (FeS) in the tube

• Proteus mirabilis
• Escherichia coli
• Enterobacter cloacae

• if tube turns black - sulfur was reduced
• if tube remains yellow - sulfur was not reduced