MICR221 Lecture 2 - Bacterial Nutrition Flashcards
what are the 2 types of culture media?
defined media
complex media
what are the 4 requirements of a defined media
the exact composition is known
every component is known
every amount of the components are known
made with specific chemicals (amino acids, specific sugars and vitamins)
what are the 3 requirements of complex media?
the exact composition is not known
not chemically pure
uses a complex source of nutrients (glucose, yeast extract, beef extract, peptones)
what is transport media?
the temporary storage of specimens that are being transported to the lab while maintaining the viability of all organisms in the specimen without cell division occurring
what does transport media contain?
contains buffers and salts for protection
what does transport media lack?
lacks carbon, nitrogen and organic growth factors
what is enriched media?
used to harvest many types of microbes by generally also encouraging the growth of “fussy” bacteria
what does enriched media provide?
through general nutrient supplements such as serum or east extract, it provides precursor metabolites
what is an enrichment broth?
provides a competitive edge to the desired microbe by encouraging the growth of a particular organism to allow the desired microbe to become the dominant species, commonly used in clinical laboratory
what is an example of an enrichment broth?
a faecal specimen is suspected of containing salmonella and concentrations of pathogens in the human body tend to be low whereas the concentration of intestinal normal microflora is high. Tetrethionate broth (an enrichment broth) holds the normal flora in the lag phase of growth while promoting the exponential growth of the pathogen salmonella.
what enzyme does salmonella contain?
contains tetrathionate reductase enzyme
what is selective media?
encourages the growth of some organisms while specifically inhibiting the growth of others and is used to distinguish between specific microbes
what is an example of selective media in terms of mannitol salt agar?
mannitol salt agar contains the general nutrients to support growth as well as a selective ingredient which is 7.5% NaCI which inhibits all except staphylococci therefore it selects for staphylococci
what is an example of selective media in terms of hektoen agar?
hektoen agar contains bile salts which inhibit gram-positive and some (non-enteric) gram-negative bacteria therefore it selects for gram-negative (enteric) gut bacteria
what is differential media?
contains a colour indicator to distinguish between organisms which allow for preliminary identification
what is an example of differential media?
mannitol (sugar) salt agar and phenyl red (pH) indicator. When the mannitol is fermented, acid is produced. Mannitol fermenters (S.Aures) change the agar colour from pink to yellow (yellow indicates the presence of pathogens). Non-mannitol fermenters (S.epidermis) agr colour remains unchanged thus stays pink
what is a batch culture?
theoretical growth of a closed system bacterial batch culture (liquid) that is incubated under ideal conditions that present a characteristic growth curve.
what is a continuous culture?
an open system as the material is being taken in and removed to maintain bacterial growth in the phase of interest, usually the exponential phase. This produces useful components such as primary and secondary metabolites
what are primary metabolites?
enzymes and amino acids produced during the exponential phase that are essential for the growth of the microbe
what are secondary metabolites?
helpful for other microbes even if they aren’t essential for the microbe that produced them, they are not essential for growth and accumulate during the stationary phase
what does a chemostat consist of?
a sterile air inlet fresh medium culture flask spent medium removed wastes and excess microbes
what does a chemostat produce?
produces a continuous open system
what are the 5 phases of microbial growth?
lag phase exponential phase stationary phase death phase long-term stationary phase
what is the lag phase of microbial growth?
components required for binary fission are synthesised however there is no cell division and this is often a very short phase but depends on chemical/physical factors
what is the exponential phase of microbial growth?
when there is a constant rate of cell division by binary fission usually represented by a steep slope upwards.. This is when the chemical and physical properties of bacteria are the most uniform
what is the stationary phase of microbial growth?
where all nutrients have been used up and either a limiting agent is produced and/or cell waste has become toxic preventing growth media from supporting rapid growth creating a static (steady) growth/death rate
what is the death phase of microbial growth?
where cell death outnumbers cell growth
what is the long-term stationary phase of microbial growth?
where there is a balance in cell growth and cell death with slight fluctuations
when does a long-term stationary phase of microbial growth occur?
occurs in a liquid, closed batch system
what are the 3 methods for measuring microbial growth?
counting chambers
turbidity of solution
viable counting
what is the counting chamber method for measuring microbial growth?
the number of microbes are counted specifically
what is the turbidity of the solution method for measuring microbial growth?
measures the optical density of the solution that is determined by the number of microbes present
what is the viable counting method for measuring microbial growth?
only living bacteria are counted
what is the disadvantage of the counting chamber and turbidity of solution methods?
both direct methods count dead microbial cells and this can create an inaccurate representation of the number of living microbes
what is the disadvantage of the viable counting method?
is very slow at producing results however the most accurate
