edited chapter 6 micro exam 2

"What are the physical requirements for microbial growth?"

"Temperature: Minimum, optimum, and maximum growth temperatures for each strain.

pH: The acidity or alkalinity of the environment affects growth.

Osmotic pressure: The concentration of solutes in the environment influences microbial survival."

"What chemical requirements are essential for microbial growth?"

"Carbon: A primary building block for microbial cells.

Nitrogen, sulfur, and phosphorus: Essential for nucleic acids and proteins.

Trace elements: Required in small amounts for various enzymatic functions

.Oxygen: Necessary for aerobic organisms; some require it, while others do not

.Organic growth factors: Vitamins and other organic compounds needed for growth."

"How is microbial growth defined in microbiology?"

increase in the number of cells, not the size of individual cells.

This term can apply to both mixed populations and colonies derived from a single bacterium."

physical requirement temperature

every strain has a

minimum growth temperature

optimal growth temperature

maximum growth temperature

"What temperature range do psychrotrophs thrive in, and why is it significant?"

between 0ºC and 20–30ºC, making them capable of thriving in refrigerator conditions.

They are responsible for food spoilage, which poses a risk to food safety."

"What are the implications of food preservation temperatures on microbial growth?"

"Temperatures that destroy most microbes can take longer at lower levels

.Refrigerator temperatures may slow spoilage bacteria growth but allow some bacteria to survive

.No significant growth occurs below freezing, which is crucial for food storage."

"What is the difference between food poisoning and food infection?"

"Food poisoning occurs when toxins produced by microbes are consumed

.Food infection involves the consumption of living microorganisms that establish an infection in the host, causing symptoms."

"What factors affect the cooling rate of food in a refrigerator and its chance of spoilage?"

"The amount of food affects how quickly it cools; larger quantities take longer to reach safe temperatures

.Temperature ranges where specific bacteria, like Bacillus cereus, can multiply increase the risk of spoilage."

"What are the typical onset times for food intoxication and food infection?"

intoxication= Onset usually within 8 hours post-ingestion.

Food infection: Onset usually 12-18 hours post-ingestion."

"What are the pH requirements for different types of microorganisms?"

"Bacteria grow best between pH 6.5 and 7.5.

Molds and yeasts thrive between pH 5 and 6.

Acidophiles grow in acidic environments."

"How does osmotic pressure affect bacterial growth?"

"Hypertonic environments cause plasmolysis, inhibiting cell growth.

Extreme halophiles require high osmotic pressure, while facultative halophiles can tolerate it."

"What is plasmolysis and how does it occur?"

when a cell is in a hypertonic solution, causing water to leave the cell.

This results in the cell's growth being inhibited due to the loss of water."

"What are the chemical requirements for bacteria regarding carbon?"

"is essential for structural organic molecules and as an energy source.

Chemoheterotrophs use organic carbon sources, while autotrophs utilize CO2."

"What role does nitrogen play in bacterial metabolism?"

"is necessary for the synthesis of amino acids and proteins.

Most bacteria catabolize proteins for nitrogen, while some use ammonium NH4+ or nitrate NO3-."

few use n2 in nitrogen fixation=bioavailability

"What are the chemical requirements for sulfur and phosphorus in bacteria?"

"sulfur is needed for amino acids, thiamine, and biotin; bacteria often catabolize proteins for it.

Phosphorus is essential for DNA, RNA, ATP, and membranes, sourced from phosphate ions."

"What are trace elements and why are they important for bacteria?"

"Trace elements are inorganic elements required in small amounts for various bacterial functions

.Examples include potassium, magnesium, and calcium, with requirements varying by species."

"What are the toxic forms of oxygen that can cause oxidative damage to cells?"

"Singlet Oxygen

Superoxide Radicals

Peroxide Anion

Hydroxyl Radical"

obligate aerobe

require oxygen in a tube of media will only grow at the top

facultative anaerobe

can grow in both env, prefer oxygen, growth throughout more at top

obligate anaerobe

only grow WITHOUT o2, only growth at bottom of tube

aerotolerant anaerobes

don’t prefer 02 will grow in o2 if has to, growth throughout tube more near bottom

microaerophiles

only require small amount of 02, grow in middle of tube

which group hates o2

obligate anaerobes

"What are organic growth factors required for microbial growth?"

"Vitamins

Amino acids

Purines

organic compounds from env

Pyrimidines"

"What are the characteristics of biofilms?"

"Clumps of bacteria adhering to surfaces by a shared polysaccharide layer

Share nutrients and are protected from harmful factors like antibiotics and the immune system"

Biofilm development is driven by .​

quorum sensing

quorum sensing is 

Each bacterium will produce a quorum sensing molecule that it secretes at all times during growth

"How does quorum sensing contribute to biofilm development?"

"Bacteria produce quorum sensing molecules during growth

High concentrations trigger genes for polysaccharide production"

"What is the definition of culture medium in microbiology?"

"Nutrients prepared for microbial growth

"

sterile

no living or dormant microbes including spores

inoculate

introduction of microbes into medium

culture

microbes growing in/on culture medium

"What is agar and its role in culture media?"

"A complex polysaccharide derived from red algae

Used as a solidifying agent for culture media

generally, not metabolized by microbes

liquefies at 100C

solidifies at 40C

"What are the two main types of culture media?"

"Chemically defined media: exact chemical composition is known

Complex media: extracts and digests of yeasts, meat, or plants"

"What is differential media in microbiology?"

"Media that distinguishes colonies based on appearance

Differences can include color, shape, or growth pattern"

"What are the characteristics of selective media in microbiology?"

"Suppress unwanted microbes while encouraging desired ones

.Example: MacConkey Agar inhibits Gram-positive organisms, making it selective for Gram-negative bacteria."

"What is the purpose of differential media in microbiology?"

"Differentiate between different types of microorganisms based on their biochemical properties.

Help identify specific bacteria by visual changes in the medium."

"How does an enrichment culture work?"

"Encourages the growth of a specific microbe from a mixed population.

Example: Culturing phenol-degrading bacteria from a soil sample by using phenol-containing medium."

A soil sample contains a few phenol-degrading bacteria and thousands of other bacteria. You want to culture the phenol-degrading bacteria:​

• Inoculate phenol-containing culture medium with thesoil, and incubate​

• Transfer 1 ml to another flask of the phenol medium,and incubate​

• Transfer 1 ml to another flask of the phenol medium, and incubate​

• Only phenol-metabolizing bacteria will be growing​

"What are anaerobic culture conditions and their requirements?"

"Conditions that prevent oxygen from affecting microbial growth.

Use reducing media and airtight growth chambers or jars with gas-producing sachets."

reducing media anaerobic culture conditions

Contain chemicals (thioglycolate or oxyrase) that combine O2​

Heated to drive off O2

Must be cultured in an air-tight growth chamber.​

"What is a pure culture in microbiology?"

"A culture that contains only one species or strain of microorganism.

Derived from a single cell or colony-forming unit (CFU)."

colony

is a population of cells arising from a single cell orspore or from a group of attached cells

"What methods are used to isolate pure bacterial cultures?"

"Quadrant streak method

.T streak method."

"What are the methods for preserving bacterial cultures?"

"Deep-freezing at temperatures between –50 to –95ºC

.Lyophilization (freeze-drying) at –54 to –72ºC, followed by dehydration in a vacuum."

"What is binary fission in bacteria?"

"A method of asexual reproduction where a single cell elongates and DNA is replicated

cell wall and plasma membrane constrict

cross wall forms completely separating the two DNA copies

cells separate 

"What is generation time in bacterial growth?"

"Generation time is the time required for a cell to divide

.For bacteria, this typically ranges from 1 to 3 hours."

"What are the phases of bacterial growth?"

"Bacterial growth phases include lag, log, stationary, and death phases.

Each phase represents different growth dynamics and metabolic activity levels."

lag phase

intense activity preparing for population growth but no increase in population

log phase

exponential or logarithmic increase in population

stationary

period of equilibrium; death and new cells balance

death

population is decreasing at logarithmic rate

"How can bacterial growth be measured?"

"Bacterial growth can be measured using direct and indirect methods.

Common direct methods include serial dilutions and plate counts, while

indirect methods often involve turbidity estimation."

"What is the process for serial dilutions and plate counts?"

"Incubate plates overnight and count colonies yielding reasonable numbers (20-200).

Calculate the number of bacteria/ml using the formula: Number of colonies × reciprocal of dilution."

"How do you determine the CFU/ml of a bacterial sample?"

"Use the formula: (# of colonies) × (dilution factor) / (volume plated)

.Typically, 0.1 ml of each sample is plated for counting."

"What is turbidity estimation in measuring bacterial numbers?"

"Turbidity estimation involves measuring the optical density (OD) of a bacterial suspension.

The standard measurement is at a wavelength of 600nm, known as OD600."

"What factors can affect turbidity estimation of bacterial numbers?"

"Factors include cell size, polysaccharide production, and the presence of dead cells.

Dead cells can block light but do not contribute to growth on plates."