PREPARATION OF BACTERIAL CULTURE MEDIA Flashcards
is the process of growing microorganisms in culture by taking bacteria from the infection site by some means of specimen collection and growing them in the artificial environment of the laboratory.
Cultivation
are incorporated into culture media on or in which bacteria are grown.
Nutrients
Nutrients usually include…
proteins/peptides/amino-acids, carbohydrates, essential metals and minerals like calcium, magnesium, iron, phosphates, sulphates etc.
such as phosphates and acetates are also incorporated.
Buffering agents
Various types of culture media have been developed for use in diagnostic microbiology because different pathogenic bacteria have different nutritional needs.
For certain bacteria that require complex and exceptional media components such as growth factors and vitamins, these bacteria are said to be..
fastidious.
the nutritional needs of most clinically important bacteria are relatively basic and straightforward and are considered…
non-fastidious.
In diagnostic bacteriology there are four general categories of media:
enrichrent (or enriched)
supportive (general)
selective
differential
_ These contain specific nutrients required for the growth of bacterial pathogens that may be present alone or with other bacterial species in a patient specimen.
Enriched media
This media type is used to enhance the growth of a particular bacterial pathogen from a mixture of organisms by using nutrient specificity.
Enriched media
One example of such a medium is buffered charcoal yeast extract agar, which provides L-cysteine and other nutrients required for the growth of Legionella pneumophila, the causative agent of legionnaire’s disease.
Enriched media
is similar to enriched media, however, this is in liquid form.
• Enrichment media
Twe enrichment broths generally used for stool specimens are_______ for alkaline-loving bacteria like the Vibrio species and _______ to enhance Salmonella and Shigella growth.
• Enrichment media
alkaline peptone water (APW)
Selenite-F
These contain nutrients that support growth of most non-fastidious organisms without giving any organism a growth advantage, for example, Nutrient Agar.
Supportive media
• These contain one or more agents that are inhibitory to all organisms except those being sought.
Selective media
These media select for the growth of certain bacteria to the disadvantage of others.
Inhibitory agents used for this purpose include…
Selective media
dyes, bile salts, alcohols, acids, and antibiotics
An example of a selective medium is________, which inhibits the growth of aerobic and facultatively anaerobic grarn-negative rods and allows gram-positive cocci to grow.
phenylethyl alcohol agar
• These employ some factor (or factors) that allows colonies of one bacterial species or type to exhibit certain metabolic or culture characteristics that can be used to distinguish them from other bacteria growing on the same agar plate.
Differential media
One commonly used differential medium is the______, which differentiates between grarn-negative bacteria that can and cannot ferment the_____.
MacConkey agar
sugar lactose
Of importance, many media used in diagnostic bacteriology provide more than one function.
For example, _______is both differential and selective because it will not allow most gram-positive bacteria to grow.
MacConkey agar
Another example is_______.
This is the most used supportive medium for diagnostic bacteriology because it allows many organisms to grow.
However, in many ways this agar is also differential because the appearance of colonies produced by certain bacterial species is readily distinguishable.
sheep blood agar.
Storage: Stack agar plates upside down in the refrigerator. Do Not Freeze!
Why?
The purpose of placing the plates upside down is to prevent condensation from dripping down onto the agar surface which could then facilitate swarming of organisms or cause contamination.
CULTURE MEDIA
• provides the________ for microbial growth
appropriate biochemical and biophvsical environment
Culture media: 2 Types
- Inoculum
- Culture
3 types of culture
Pure
Mixed
Stock
