MICR 290 LAB FINAL

Comprehensive vocabulary flashcards covering microbial control, selective/differential media, biochemical tests, and quantitative food safety methods from the Lab Final Study Guide.

UV-C

The most effective UV light against microbes because it has the shortest wavelength and the highest energy, which allows it to damage microbial DNA.

Thymine dimers

Mutations caused by UV light where two adjacent thymine bases in DNA strands bond together, preventing replication and transcription.

Young vs. Old Cultures Sensitivity

Young, actively dividing cultures are more sensitive to UV radiation because their DNA is being replicated rapidly, making them more vulnerable to damage.

Zone of Inhibition

The clear area around an antibiotic disk where bacterial growth is inhibited; a large zone indicates sensitivity, while a small or no zone indicates resistance.

Mueller-Hinton agar

A standardized medium used for antibiotic sensitivity tests because it allows antibiotics to diffuse evenly and supports the growth of many bacteria without interference.

Glo-Germ Experiment

An experiment using glowing particles to demonstrate how microorganisms and contamination spread through contact and to show the importance of proper handwashing.

Mannitol Salt Agar (MSA) Selective Principle

Selective because it contains $7.5\%$ sodium chloride, which inhibits most bacteria except salt-tolerant organisms like Staphylococcus species.

Mannitol Salt Agar (MSA) Differential Principle

Differential because it contains mannitol sugar and the pH indicator phenol red to distinguish bacteria that can ferment mannitol.

Staphylococcus aureus (on MSA)

A bacterium that ferments mannitol, resulting in acid production that turns the agar yellow.

Staphylococcus epidermidis (on MSA)

A bacterium that does not ferment mannitol, resulting in little or no color change, with the agar remaining pink or red.

Eosin Methylene Blue (EMB) Agar Selective Principle

Selective because it contains eosin and methylene blue dyes that inhibit the growth of most Gram-positive bacteria.

Eosin Methylene Blue (EMB) Agar Differential Principle

Differential because it contains lactose; fermentation of lactose causes color changes in the bacterial colonies.

Coliform bacteria

Gram-negative, lactose-fermenting bacteria used as indicator organisms because their presence suggests possible fecal contamination and potential pathogens.

Escherichia coli (on EMB)

A strong lactose fermenter that typically produces a distinctive metallic green sheen on EMB agar.

Reactive Oxygen Species (ROS)

Toxic forms of oxygen that include hydrogen peroxide ($H_2O_2$), superoxide radicals, and hydroxyl radicals.

Catalase

An enzyme that protects cells from toxic hydrogen peroxide by breaking it down into water ($H_2O$) and oxygen ($O_2$).

Catalase Test Examples

Staphylococcus species are catalase-positive, while Streptococcus species are catalase-negative.

Cytochrome c oxidases

Enzymes involved in the electron transport chain during aerobic respiration, detected using the oxidase test.

Oxidase Test Results

A positive result is indicated by a dark purple or blue color appearing quickly; a negative result shows no color change. The oxidase test detects the presence of cytochrome c oxidase enzyme in bacteria.

Oxidase-Positive vs. Negative Microbes

Pseudomonas and Neisseria are oxidase-positive, while Escherichia coli and Enterobacter are oxidase-negative.

FDA Milk Count Standards

Before pasteurization, raw milk should contain no more than $100,000$ bacteria per mL, and mixed samples must be less than $3 \times 10^5$ organisms per mL.

Statistically Reliable Plate Count

A plate containing between $30$ and $300$ colonies is considered reliable for counting bacteria accurately.

TFTC and TNTC

TFTC stands for Too Few To Count (less than $30$ colonies); TNTC stands for Too Numerous To Count (more than $300$ colonies).

Standard Plate Count (SPC) Formula

$\text{CFU/mL} = \frac{\text{Number of colonies} \times \text{Dilution factor}}{\text{Volume plated}}$ → use 0.05 as the volume in mL; dilution factor always positive

What do 1:10, 1:100, 1:1000 mean with different volumes (basic dilutions)?

1:10 dilution → 1 mL sample + 9 mL diluent Total = 10 parts

1:100 dilution → 1 mL of 1:10 dilution + 9 mL diluent

1:1000 dilution → 1 mL of 1:100 dilution + 9 mL diluent

Each dilution decreases the number of bacteria by a factor of 10.