lab pt 3

What do sediment, pellicle, and flocculent growth look like?

Sediment: growth at the bottom; pellicle: growth layer at the surface; flocculent: suspended clumps or flakes.

What does a turbid broth indicate?

Bacterial growth in liquid medium.

What is a growth medium?

A nutrient-containing material used to grow microorganisms.

How are growth media generally prepared?

Measure dehydrated medium, dissolve in water, heat if needed, dispense, sterilize, and cool.

How are most culture media sterilized?

Using an autoclave, which sterilizes with pressurized steam.

What are common autoclave conditions?

Approximately $121\,^\circ\text{C}$, $15\,\text{psi}$ above atmospheric pressure, for $15\,\text{minutes}$, depending on the load.

What is an all-purpose medium and when is it used?

A general-purpose medium supporting many nonfastidious organisms; used for routine cultivation and maintenance.

What is a chemically defined medium?

A medium in which the exact chemical identity and amount of every ingredient are known.

When is a chemically defined medium used?

To study specific nutritional requirements and metabolic activities.

How do defined and complex media differ?

Defined media have known exact compositions; complex media contain ingredients such as extracts and digests whose exact composition is not fully known.

What is a pure culture?

A culture containing only one species or strain of microorganism.

What is a bacterial colony and what is a pure colony?

A colony is visible microbial growth, usually originating from one colony-forming unit. An isolated colony can be used to obtain a pure culture.

What is the streak plate method?

A technique that spreads bacteria across agar in successive streaks to separate individual cells.

How does the streak plate method obtain isolated colonies?

Each successive streak reduces the number of bacteria deposited, separating individual cells that grow into colonies.

Why is the inoculating loop sterilized between streak sections?

To reduce the number of bacteria transferred into each successive section.

Why is obtaining isolated colonies important?

It allows individual bacterial species to be studied without interference from other organisms.

Why is it difficult to obtain completely bacteria-free hands?

Microorganisms naturally live on and within the skin, including deeper skin layers, follicles, and creases.

What are resident and transient microorganisms?

Resident: normally live on skin and are difficult to remove completely. Transient: temporarily acquired through contact.

What is the difference between handwashing and sterilization?

Handwashing removes many microorganisms; sterilization eliminates all forms of microbial life.

Why is handwashing important even though hands cannot be completely sterilized?

It significantly reduces transient microorganisms and lowers the spread of pathogens.

What are anaerobic bacteria?

Bacteria that can grow without oxygen.

How do obligate aerobes, obligate anaerobes, and facultative anaerobes differ?

Obligate aerobes require oxygen; obligate anaerobes cannot grow in oxygen; facultative anaerobes grow with or without oxygen but usually better with it.

What are aerotolerant anaerobes and microaerophiles?

Aerotolerant anaerobes do not use oxygen but tolerate it; microaerophiles require oxygen at lower-than-atmospheric concentrations.

Why are anaerobic environments used?

To grow and identify bacteria that cannot grow in normal atmospheric oxygen.

How does an anaerobic jar work?

It removes oxygen or chemically converts it into water, creating an oxygen-free environment.

What is a GasPak system?

A system that generates gases, including hydrogen, which reacts with oxygen to form water, usually with a palladium catalyst.

What is the purpose of an anaerobic indicator?

To verify whether oxygen has been removed from the environment.

How does methylene blue indicate anaerobic conditions?

It is colorless without oxygen and blue when oxygen is present.

What is an anaerobic chamber?

A sealed workspace maintaining an oxygen-free atmosphere for handling and growing anaerobes.

What is an anaerobic pouch or bag?

A sealed container with an oxygen-removing system for creating anaerobic conditions.