growth & nutrition of bacteria Flashcards
define bacterial growth
- growth is an increase in the number of cells (not an increase in size)
define generation time?
- is the time it takes for a cell to divide & the bacteria population to double
- bacteria divide by binary fission
list the 4 phases of the bacterial growth curve?
- lag phase
- logarithmic phase
- stationary phase
- death or decline phase
describe the lag phase of the bacterial growth curve
- lag phase occurs immediately after inoculation into fresh medium
- bacteria increase in size not number as they are increasing their metabolic activity
what does the length of the lag phase depend on?
- size of inoculum
- time to recover from transfer into medium
- time for synthesis of coenzymes or division factors
- time for new enzyme synthesis needed for metabolising substrates is media
describe the log phase of the bacterial growth curve?
- in log phase, cells divide at a constant rate by binary fission
- rate is dependent on: composition of growth medium & conditions of generation time
describe the stationary phase of the bacterial growth curve
bacterial growth plateaus due to:
- exhaustion of essential nutrients
- increase in toxic metabolites
- exhaustion of space
describe the death or decline phase in the bacterial growth curve
- during decline phase viable cell count population declines
viable count = just alive cells, total count = alive & dead cells
what is the use of a continuous culture?
- prevents death & decline phase
- bacterial cultures are maintained in a state of exponential growth over a long period of time
- uses a chemostat
causes of variations in generation time for different pathogens (2)
- serum resistance - allows some pathogens to have higher doubling times in host tissue
- virulence factors - allows some pathogens to have a long generation time (host immune system not triggered quickly by these bacteria)
what does measuring bacterial growth involve? what are the 3 methods for measuring bacterial growth?
- involves estimating the number of cells that arose from binary fission during growth phase
- methods:
1. viable count
2. total cell count (direct microscopic count & turbidity)
3. real-time PCR
what does a viable count involve for measuring bacterial growth?
- involves serial dilutions plated onto solid media
- only living bacteria will divide & form a visible colony on agar plate that can be counted to estimate bacteria growth
what are the advantages & disadvantages of using a viable count to measure bacterial growth?
advantages
- quantitative
- can identify the bacteria
disadvantages
- only living cells develop colonies that are counted
- clumps of cells can develop into a single colony - reduces accuracy
- need correct culture conditions
when measuring bacterial growth, what does a direct microscopic count involve?
- estimating the concentration of bacteria in media
- counts all cells both living & dead (total count)
- uses a cell counting chamber
when measuring bacterial growth, what does the turbidity method involve?
- turbidity method estimates large numbers of bacteria in a clear liquid media & broth
- optical density of suspension is directly related to cell number
- spectrophotometer can be used to count cells
- McFarland turbidity standard can be used to estimate number of cells in suspension
what are the requirements for bacterial growth
- physical requirements - temp, pH, osmotic pressure, oxygen
- chemical requirements - carbon, nitrogen, sulphur & phosphorous, trace elements & growth factors
what are the requirements for different anaerobes? (obligate anaerobes, facultative anaerobes, aerotolerant anaerobes)
- obligate anaerobes = die in presence of O2
- facultative anaerobes = can grow with or without oxygen
- aerotolerant anaerobes = can survive in presence of O2 but do not use it for metabolism
what is the optimum growth temperature, pH & osmotic pressure for MOST pathogenic bacteria?
- most pathogens are mesophiles: grow at 15-45C with optimum around 37C
- most bacteria prefer a neutral pH
- require isotonic osmotic pressure -> hypertonic environment cause plasmolysis of bacteria (increased salt or sugar)
what are growth factors?
- organic compounds obtained from the environment (vitamins, amino acids, purines & pyrimidines)
- must be supplied by environment for cell to survive & reproduce as cell cannot synthesise them
what are fastidious organisms?
- bacteria that require a medium with various growth factors or other components & are hard to grow
what does the aseptic technique involve for growing bacteria in the laboratory?
- sterile media
- sterilisation & disinfection to prevent contamination
what are the 6 different type of growth media for growing bacteria?
- solid media - for isolation of single colonies
- liquid media - for growing large numbers of bacteria
- semisolid media - for
demonstration of motility - routine media - basic nutritive media capable of growing less fastidious bacteria
- enrichment media - permits growth of a specific bacteria
- enrichment broth - used for organisms in low numbers or swapped by other bacteria
what is selective media?
- media that select for particular groups of bacterial pathogens
- contains inhibitors which suppress the growth of unwanted bacteria
what is differential media used for?
- for differentiation of 2 species or groups
- makes it easy to distinguish colonies of different microbes
what is MacConkey Agar used for?
it it selective
- contains components that inhibit growth of some bacteria & promotes growth of other
- most gram +ve will not grow
- enterobacteria will grown
it is differential
- bacteria that ferment lactose will be pink
- backer that cannot ferment lactose will be yellow
what is blood agar used for?
is an enrichment media (blood for fastidious organism)
it is differential
- certain bacteria produce enzymes that lyse red blood cells
& produce a colour change
not selective
- supports growth of a wide range or organisms
define a strict bacterial parasite
- bacteria that can only use a small number of substrates
define an opportunist bacterial organism
- bacteria that can utilise many substrates
