Lab Exam 3 Flashcards
What changes occur in Mannitol Salt Agar and Blood Agar for Staphylococcus aureus?
Mannitol Salt Agar: yellow zones mean Mannitol fermentation
Blood Agar: Beta hemolysis produces clear zones
What enzyme does the starch hydrolysis test detect?
Amylase.
What medium is used for the starch hydrolysis test?
Starch plate.
What is the reaction in the starch hydrolysis test?
Starch is broken down into sugar.
What visual cue indicates a positive starch hydrolysis test?
A clear zone after iodine flooding.
What enzyme does the casein hydrolysis test detect?
Caseinase.
What medium is used for the casein hydrolysis test?
Casein (milk) agar.
What is beta hemolysis?
complete lysis of red blood cells
how does beta hemolysis appear on Blood Agar?
clear zones
What visual cue indicates a positive casein hydrolysis test?
A clear zone around the colony.
What enzyme does the fat hydrolysis test detect?
Lipase.
What is the pH indicator in Mannitol Salt Agar, and what is the salt concentration?
pH indicator: phenol red
Salt concentration: 7.5%
What medium is used for the fat hydrolysis test?
Peanut oil agar with neutral red.
What visual cue indicates a positive fat hydrolysis test?
Red droplets around and under the colony.
What enzyme does the tryptophan hydrolysis test detect?
Tryptophanase.
What reagent is used in the tryptophan hydrolysis test?
Kovac’s reagent.
What visual cue indicates a positive tryptophan hydrolysis test?
A red/pink layer (ring) forms on top of the medium.
Identify each WBC
___________: multi-lobed nuclei ) 60-70%
___________: bi-lobed nuclei 20-25%
___________: lobed or irregular nucleus
___________: large, kidney-shaped or horseshoe-shaped nucleus
___________: large, round nucleus that occupies most of the cell
Neutrophil
Eosinophil
Basophil
Monocyte
Lymphocyte
What enzyme does the urea hydrolysis test detect?
Urease.
What visual cue indicates a positive urea hydrolysis test?
Bright pink color.
What pH indicator is used in the urea hydrolysis test?
Phenol red.
What three tests are included in the SIM test?
Sulfide, Indole, and Motility.
What medium is used for the SIM test?
SIM medium.
What indicates sulfide production in the SIM test?
Black precipitate.
What indicates indole production in the SIM test?
A red ring forms after adding Kovac’s reagent.
How is motility detected in the SIM test?
Diffuse growth away from the stab line.
What does the citrate utilization test detect?
Citrate metabolism.
What medium is used for the citrate utilization test?
Simmons Citrate Agar.
What visual cue indicates a positive citrate utilization test?
Blue color.
What enzyme does the phenylalanine deamination test detect?
Phenylalanase.
What reagent is used in the phenylalanine deamination test?
Ferric chloride.
What visual cue indicates a positive phenylalanine deamination test?
Dark green color.
What is the appearance of coliforms on Endo agar?
metallic sheen colonies
What is transformation?
The uptake of DNA from the environment.
What is a plasmid?
Small circular DNA that gives bacteria extra traits, like antibiotic resistance.
What process gives rise to fluorescent colonies?
Transformation with a plasmid.
What is an antiseptic?
A chemical used on living tissues to reduce microbial load.
What sugar is in the differential medium for detecting fecal coliforms?
Lactose
What method tests sensitivity to antiseptics and disinfectants?
Disk diffusion method.
At what temperature are fecal coliform cultures incubated?
44°C
How do Staphylococci appear under a microscope?
Cocci in clusters.
What is the purpose of Mannitol Salt Broth?
To enrich for staphylococci by selecting for salt-tolerant species.
What is the purpose of Mannitol Salt Agar?
differentiate species based on mannitol fermentation.
What is the pH indicator in Mannitol Salt Agar?
Phenol red.
Why is Bergey’s Manual important?
most important single source of information for bacterial identification
What visual cue indicates S. aureus on Mannitol Salt Agar?
Yellow colonies and agar.
What test confirms pathogenic S. aureus?
Coagulase test.
What visual cue indicates a positive coagulase test?
Plasma coagulates into a gel.
What bacteria are used in yogurt production?
L. bulgaricus and S. thermophilus.
How are antibiotics tested for sensitivity?
What agar is used?
Using Kirby-Bauer disk diffusion method and placing paper disks on lawn of bacteria
Mueller-Hinton Agar
What ingredients are needed to make yogurt?
Milk and a starter culture.
Is yogurt acidic or alkaline?
Acidic.
What is the difference between an antimicrobial and an antibiotic?
Antimicrobials: target, kill, or inhibit growth of all microorganisms
Antibiotics: ONLY target bacteria
What is the mechanism of action of Penicillin and Ampicillin?
Disruption of cell wall synthesis.
What is the mechanism of action of Tetracycline, Erythromycin, and Streptomycin?
Disruption of protein synthesis
Which antibiotic is effective only against Gram-positive bacteria?
Penicillin
What is Durham Tube Sugar Fermentation testing for?
Fermentation of sugar w/ acid production and gas production.
What media is used in Durham Tube Sugar Fermentation?
Phenol red broth with sugar and a Durham tube
What reaction is being tested in Durham Tube Sugar Fermentation?
Sugar fermentation producing acid and/or gas.
What pH indicator is used in Durham Tube Sugar Fermentation?
Phenol red
What is the visual cue for positive/negative results in Durham Tube Sugar Fermentation?
Yellow= acid production (+)
Bubble in the Durham tube= gas production.
No color change= negative (-)
What is the Methyl Red Test testing for?
Mixed acid fermentation
What media is used for the Methyl Red Test?
MR-VP broth
What reaction is being tested for the Methyl Red Test?
stable acidic end-products from glucose fermentation.
What pH indicator is used?
Methyl red reagent
What is the visual cue for positive/negative results?
Red =a positive result
yellow = a negative result.
What is the Voges-Proskauer Test testing for?
Production of acetoin from glucose fermentation.
What media & reagents is used for the Voges-Proskauer test?
Media: MRVP broth
Reagents: alpha-napthol & KOH
What reactions are tested in the Voges-Proskauer test?
acetoin production from glucose fermentation and its conversion to diacetyl in the presence of Barritt’s reagents.
What are the visual cues and pH indicators in the Voges-Proskauer test?
red color = positive (+)
No color change = (-)
What is the purpose of the catalase test?
identify organisms that produce the enzyme catalase
What media is used for the catalase test?
No specific media is used; the test is performed directly on a slide or agar plate
What enzymes and reactions are tested in the catalase test?
detects catalase, an enzyme that converts hydrogen peroxide into water and oxygen gas
What are the visual cues in the catalase test?
Bubbling = positive (+)
No rxn = negative (-)
What is the purpose of the oxidase test?
determine if an organism produces cytochrome c oxidase, an enzyme involved in the electron transport chain
What media is used for the oxidase test?
No specific media is required;
filter paper or a swab with oxidase reagent.
What enzymes and reactions are tested in the oxidase test?
cytochrome c oxidase, which transfers electrons to oxygen during aerobic respiration
What are the visual cues in the oxidase test?
purple or dark blue color change within 20 seconds
What is the purpose of the Gelatin Hydrolysis test?
to see if an organism produces gelatinase, an enzyme that hydrolyzes gelatin
What media is used for the gelatin test?
Nutrient gelatin
What enzymes and reactions are tested in the gelatin test?
presence of gelatinase, which breaks down gelatin into its constituent amino acid
What are the visual cues in the gelatin test?
There will be a clear zone around a colony that produces
gelatinase.
How do you distinguish between Staphylococcus and Streptococcus in terms of catalase test?
Staph is catalase positive, while Strep is catalase negative.
In citrate test, Simmons citrate medium contains citrate and the pH indicator?
bromocresol green.
