Microbio test 1

Media used in oxygen tolerance test; Fluid thioglycollate medium (FTM)

Indicator in oxygen tolerance test media; Resazurin

Indicator and inhibitor in MSA; Phenol red (indicator), NaCl (inhibitor)

Bacteria that grow on MSA; Halotolerant Gram-positive (e.g., Staphylococcus)

Indicator and inhibitor in MacConkey; Neutral red (indicator), bile salts and crystal violet (inhibitor)

Bacteria that grow on MacConkey; Gram-negative enteric rods

Difference between alpha, beta, gamma hemolysis; Alpha – partial green, Beta – complete clearing, Gamma – no hemolysis

Inhibitor in CNA and bacteria that grow; Colistin and nalidixic acid; Gram-positive bacteria

Nigrosine stains do not enter cells because both the stain and cell membrane are; Negatively charged

Purpose of using the negative staining technique; Visualize cell shape without distortion from heat-fixing

Why did Clostridium sporogenes grow in the Anaerobic box but not in the air; It is an obligate anaerobe

Which organism will grow in the air and not in the anaerobic box; Obligate aerobe

Two modes of action of antibiotics; Inhibit cell wall synthesis, inhibit protein synthesis

Difference between bactericidal and bacteriostatic chemicals; Bactericidal kills bacteria, bacteriostatic inhibits growth

Name of the antibiotic susceptibility test and media used; Kirby-Bauer test; Mueller-Hinton agar

Name of the method to spread the disease for antibiotic susceptibility test; Lawn culture with sterile swab

Which antibiotic should you use to treat the patient if the bacteria is resistant or susceptible; Use the one the bacteria is susceptible to

Will E. coli grow at 37°C after incubating first at 4°C? Why or why not; Yes, it's a mesophile and survives refrigeration

Define optimal temperature. Difference between psychrophile and mesophile; Optimal temperature is best for growth; psychrophiles prefer cold, mesophiles prefer moderate temps

Define resolution; Ability to distinguish two close points as separate

Define parfocal; Microscope stays in focus when switching objectives

Define field of view; Area visible through the microscope

Define magnification; Enlargement of an image

Name of the microscope most used in microbiology lab; Compound light microscope

Total magnification using 100X objective lens; 1000X

Purpose of immersion oil with oil immersion lens; Reduces light refraction and increases resolution

Name the structure formed in DNA caused by UV exposure; Thymine dimers

Two disadvantages of using UV for sterilization; Poor penetration, harmful to skin/eyes

Enzyme that can repair UV damage; Photolyase

Wavelength at which UV is harmful to bacteria; 260 nm

Why did we cover half of the plate while exposing bacteria to UV; To serve as an unexposed control

Which bacteria were more resistant against UV? Why; Spore-formers like Bacillus; endospores resist UV damage

Why did we use the 3-way swab technique and how; To create an even bacterial lawn; swab in three directions

Name of the instrument that sterilizes; Autoclave

Autoclave pressure; 15 psi

Autoclave temperature; 121°C

Autoclave time; 15–20 minutes

Why do we use indicators while autoclaving; To confirm successful sterilization

Identify part C and its function; Incubator; maintains optimal growth temperature

Define acidophile, basophile, neutrophile; Acidophile – grows in acidic pH, Basophile – in basic, Neutrophile – in neutral

Which microorganism grows at neutral pH; E. coli

Which grows at acidic pH; Lactobacillus

Describe 3 steps in preparation of smear (from broth); Place loopful on slide, spread, air-dry

Describe 4 steps in preparation of smear (from agar); Add water, mix colony, spread on slide, air-dry

What happens if you take too many cells when preparing smear for Gram stain; Smear is too thick, hard to interpret

What happens if you don’t heat-fix while smearing from bacteria on plate; Cells may wash off during staining

What happens if you don’t air-dry smear before heat-fixing; Cells can lyse from heat

Why stain a specimen for bright field microscopy; Increases contrast to see cells

What is the pore size of membrane filter; 0.45 µm

What does EMB stand for? Name the inhibitor and indicator; Eosin Methylene Blue; dyes act as both inhibitor and indicator

Coliforms are Gram ___ and ___ fermenting rods; Gram-negative, lactose-fermenting rods

Define commensalism; Symbiotic relationship where one benefits, other is unaffected

Define complex/rich media. Example; Contains unknown components; nutrient agar

Define synthetic media. Example; Chemically defined; glucose salts broth

Name 2 constituents of media required for bacterial growth; Carbon source, nitrogen source

What is agar concentration in broth; 0% (none)

At what temperature does agar solidify; About 42°C

Define phototroph, autotroph, chemotroph, heterotroph; Phototroph – uses light, Autotroph – uses CO₂, Chemotroph – uses chemicals, Heterotroph – uses organic carbon

Name the technique used for streak plate isolation; Quadrant streak method

Difference between pure and mixed culture? Which media to check; Pure = one species; Mixed = more than one; use selective/differential media

What happens if you don’t flame loop before quadrant streaking; Contamination can occur

How do we take culture for every quadrant; From the previous quadrant’s streak

How do we incubate plates in incubator? Why; Inverted; prevents condensation on agar

Identify stain technique on microscope A; Gram stain

Name primary stain and counterstain in Gram stain; Crystal violet (primary), Safranin (counterstain)

What is the name of the decolorizer; Alcohol or acetone-alcohol

What are the green structures? Pink structures?; Green = endospores, Pink = vegetative cells

Name bacteria (genus and species) used to prepare stain in 2042 lab; Bacillus megaterium

Identify stain technique under microscope B; Acid-fast stain

What is Gram nature of organism under B; Gram-positive

What is Gram nature of organism under C; Gram-negative

Primary stain, mordant, counterstain, decolorizer; Crystal violet, iodine, safranin, alcohol

Two reasons for using agar instead of gelatin; Agar is not degraded by microbes, stays solid at room temperature

Why are thermal death point, decimal reduction rate, and thermal death time important; They help determine effectiveness of sterilization techniques

Define osmosis; Movement of water across membrane from low solute to high solute concentration

What happens to cell in hypertonic solution; Cell shrinks (plasmolysis)

What happens to cell in hypotonic solution; Cell swells or bursts

What happens to cell in isotonic solution; No net water movement

Difference between halotolerant, obligate halophile, non-halotolerant organisms; Halotolerant – tolerates salt, Obligate halophile – requires salt, Non-halotolerant – cannot grow in salt

Volume for micropipette A; 1000 µL

Volume for micropipette B; 200 µL

Volume for micropipette C; 20 µL

Conversion: 1 mL = ___ μL; 1000 µL

Conversion: 100 µL = ___ mL; 0.1 mL

What media is used for fungi in the lab; Sabouraud dextrose agar

The study of fungi is called; Mycology

Domain of fungi; Eukarya

Two ways fungi help us; Antibiotic production, food fermentation

Define dimorphic fungi; Fungi that exist as yeast and mold forms

What is the enzyme that detoxifies hydrogen peroxide; Catalase

Name of the test performed in the image shown; Catalase test

Which side shows a positive result; Side with bubbles

Name an organism in BIOL 2042 lab negative for this test; Streptococcus spp.

Name an organism positive for this test; Staphylococcus spp.

What reagent is used for this test; Hydrogen peroxide

Identify the staining technique used on microscope A; Acid-fast stain

Name of the primary stain and counter stain used in this stain; Carbol fuchsin (primary), Methylene blue (counterstain)

Name of the decolorizer; Acid-alcohol

What are the red structures seen; Acid-fast cells

What are the blue structures seen; Non-acid-fast cells