Microbiology and Food Preservation

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the minimum temperature to which the medium should be cooled?

60 °C

45 °C

50 °C (correct)

55 °C

Why is it necessary to flame the lip of the bottle whenever the lid is replaced?

To speed up the cooling process

To remove excess moisture

To prevent contamination (correct)

To add antibiotics to the medium

What is the purpose of incubating the plates at 37 °C for 48 hours?

To dry out excess moisture

To promote the growth of microbes

To cool the medium further

To check for sterility and dry out excess moisture (correct)

What should be done if there is growth of microbes on the surface of any of the agar plates?

Discard the particular agar plate Signup and view all the answers

How much of the plate surface should be covered with the medium?

One-half Signup and view all the answers

What is the purpose of using disinfectants or sterilization methods in laboratories?

To kill or inactivate microorganisms Signup and view all the answers

What is the primary consideration when preparing a culture medium for the cultivation of a microorganism?

The nutritional requirements of the microorganism Signup and view all the answers

What is the difference between a synthetic medium and a defined synthetic medium?

A synthetic medium has unknown chemical composition, while a defined synthetic medium has known specific kinds and amounts of chemical substances Signup and view all the answers

What is the term for a culture medium that is used to isolate and purify microorganisms from a mixed culture?

Selective medium Signup and view all the answers

What is the term for a liquid culture medium?

Broth Signup and view all the answers

What is the effect of high concentration of sugar or salt on cells?

They lose water Signup and view all the answers

What is the primary function of soaps and detergents in chemical methods?

To remove microbes, oils, and dirt Signup and view all the answers

Which of the following is NOT a characteristic of a disinfectant?

It should kill all forms of life Signup and view all the answers

What is the primary function of alkali in soap?

To destroy microorganisms Signup and view all the answers

What is the primary use of chlorine?

To kill pathogens in water Signup and view all the answers

What is the primary use of phenol derivatives?

To disinfect skin, instruments, and furniture Signup and view all the answers

Why is it necessary to heat the entire metal inoculating loop in the flame?

To kill any bacteria that may be present on the loop Signup and view all the answers

What is the purpose of streaking the agar plate in quadrants?

To ensure that the bacteria are evenly distributed across the agar plate Signup and view all the answers

What is the purpose of an enriched growth medium?

To promote the growth of a particular organism by providing essential nutrients Signup and view all the answers

Why should the agar plate be opened only minimally when streaking the bacteria?

To prevent contamination from other sources Signup and view all the answers

Why are agar plates incubated upside down?

To reduce bacterial contamination and prevent water condensation from accumulating on the lid Signup and view all the answers

What is the purpose of heating the red blood cells to 56 °C in chocolate agar?

To lyse the red blood cells and provide growth factors for fastidious bacteria Signup and view all the answers

What is the purpose of autoclaving the agar preparation?

To sterilize the agar preparation Signup and view all the answers

What is the purpose of cooling the inoculating loop before picking the inoculum?

To prevent the loop from burning the agar Signup and view all the answers

What type of bacteria can be grown on chocolate agar?

Fastidious respiratory bacteria Signup and view all the answers

What is the purpose of adding distilled water to the dehydrated medium?

To dissolve the agar powder Signup and view all the answers

What is the temperature and pressure used for autoclaving?

121 °C, 15 psi Signup and view all the answers

Study Notes

Enrichment Media

Enrichment media are used to promote the growth of a particular organism by providing essential nutrients and minimizing the growth of normal competitors
Examples include chocolate agar, which is a variant of blood agar plate, containing red blood cells that have been lysed by heating to 56 °C
Used for growing fastidious (fussy) respiratory bacteria, such as Haemophilus influenza, which require growth factors like NAD and hematin found inside erythrocytes

Agar Preparation

Weight the dehydrated medium (containing agar in powder form) and add distilled water, stirring to break up clumps of powder
Pour into a glass bottle with a funnel, cap loosely, and label the bottle
Autoclave for sterilization (121 °C, 15 psi, 15-20 min) and then remove from autoclave

Media Preparation

Culture media are nutrient materials used in laboratories to grow microorganisms
A culture is a microorganism that grows and multiplies in or on a culture medium
Successful cultivation of a microorganism requires understanding its nutritional requirements and supplying essential nutrients in the proper form and proportion

Types of Media

Synthetic media: prepared in the laboratory from materials of precise or reasonably well-defined composition
Complex media: contain unknown or varying concentrations of nutrients
Selective media: allow growth of specific microorganisms and inhibit others
Differential media: distinguish between different microorganisms based on their growth characteristics
Enrichment media: promote growth of a particular organism

Aseptic Technique

Use sterile (aseptic) technique to ensure a new medium contains organisms of only a single species
Heat metal inoculating loops in a flame until red hot before picking the inoculum (broth or agar)
Cool the loops before use
Streak the agar plate with bacteria, flaming the loop between each quadrant
Label the agar plate, keeping the lid minimally open to prevent contamination

Incubation

Incubate agar plates upside down to reduce bacterial contamination and water condensation
Keep samples in an incubator at 37 °C for 48 hours to check for sterility

Chemical Methods

Disinfectants reduce the infectivity of a material, but may not kill all forms of life present
Chemical agents include soaps and detergents, acid, alkali, heavy metals, halogens, alcohols, and phenol derivatives
These agents aid in the removal of microbes, oils, and dirt, and help destroy microorganisms

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Learn about the role of osmotic pressure in preserving food and the use of chemical agents in disinfection. Discover how these methods prevent the growth of microorganisms and reduce infectivity.