Lecture 2 Flashcards
Bacterial Nutrition - cultures and growth
what are the 2 culture medias
defined and complex
defined media…
chemically pure
- know exact composition
- know every component
- know exact concentration
- make with specific chemicals
—–specific sugars, amino acids, vitamins
complex media…
not chemically pure
- do not know exact composition
- use of complex sources of nturients
—- glucose, beef extract, yeast, peptones
name the 5 specialised (complex) media
transport
enriched
enrichment
selective
differential
transport media
usually liquid
- maintains viability of organisms in specimen without cell division
- contains only buffers and salts (for protection)
lacks carbon, nitrogen, and organic growth factors
enriched media
could be liquid or solid agar
- contains GENERAL nutrient supplements (eg serum or yeast extract) to provide precursor molecules
- good for fastidious microbes (that cant produce all required precursors themselves)
enrichment media
usually liquid
- encourages a PARTICULAR ORGANISM
- gives competitive edge to the desired microbe (becomes dominant species)
example of enrichment media
tetrathionate broth for encouraging the growth of salmonella
example of selective media
mannitol salt agar - sodium chloride inhibits all except staphylococci (selective for staphylococci)
hektoen agar
bile salts - inhibits gram-positive and some (non-enteric) gram-negative bacteria (selective for gram-negative, gut, bacteria)
selective media
usually solid agar
- encourages the growth of some organisms WHILE SPECIFICALLY INHIBITING THE GROWTH OF OTHERS
what is going on in the stationary phase
essential nutrients might be used up
build up of toxic products
results in the end of the exponential phase
differential media
usually sold agar
- contains indicators that VISUALLY DISTINGUISH between organisms (colour change)
example for differential media
mannitol salt agar
what is happening in the long-term stationary phase
population phase is more or less consistent
- cell death may release nutrients used up by living cells
what are the 5 points on a growth curve for the dynamics of growth of a bacterial population
(beginning to end)
lag phase
exponential phase
stationary phase
death phase
long-term stationary phase
primary and secondary metabolites
primary
- essential for growth of microbes
- produced during logarithmic phase (exponential phase)
- eg amino acids, nucleotides
secondary
- not essential for growth
- accumulate during stationary phase
- eg antibiotics
a-haemolysis
partial lysis of RBC - green discolouration
b-haemolysis
complete lysis of RBC - complete clear zone
y-haemolysis
non-haemolytic
