Bacterial Growth Flashcards
how is microbial growth measured?
generation time- time it takes microbes to double
how do microbes reproduce?
binary fission
mycobacteria v e coli doubling time
20 hours v 20 minutes
what limits bacterial growth?
nutrient supplies/ key resources
accumulation of toxic metabolic products
antibiotics from neighboring micorbes
immune system
lag phase vs log phase vs stationary phase
lag phase- beginning where culture does not grow exponentially
log phase- exponential culture growth
stationary phase- end where culture does not grow
lag phase
occurs when bacteria encounter new environment
length depends on kind of bacteria, inoculum source, and nature of new medium
log phase
exponential growth
depends on type of organism, nature of medium, temperature
sensitive to antibiotics during this phase
stationary phase
growth slows for various reasons (pH change, decrease in oxygen)
increased resistance to antibiotics
death phase
rate of death surpasses rate of growth
can be caused by pH change
can occur after stationary phase
cell morphology can change during death phase
what must happen for a bacterium to grow
need to generate cell membrane, proteins, flagellum, chromosomes, cell wall
need carbon nitrogen and phosphorus
bacterial carbon sources
glucose, other sugars, amino acids
some bacteria can use lipids, organic acids, alcohols, polymers
how do bacteria absorb proteins
use proteases to chop up peptides and create amino acids that can be absorbed
often these proteases are virulance factors
extracellular nucleases
allows bacteria to absorb C, N, and P from host DNA
bacteria can use phospholipases to acquire C, N and P from host. using phospholipase to lyse a cell yields iron
ok
how is iron important in pathogenesis
iron is needed for ATP generation, and is conserved by the host to make less available to pathogens
ability to scavange iron is key to virulence
siderophores
high affinity for iron
make iron available to bacteria by stealing iron from host and have receptors to re-enter bacteria
how else can bacteria get iron besides siderophores
lyse open an iron rich cell
what are growth factors?
presynthesized factors that the bacteria need to grow but cannot synthesize themselves
fastidious microbes
require purines, pyrimidines, vitamins, amino acids to grow
prototropic microbes
synthesize almost everything they need to grow
requirement for growth factors can be diagnostic
ok
physical requirements for microbial growth
optimal temperature
optimal pH
high salt and sugar concentrations inhibit growth
turbidity
visual detectoin of bacteria
faint turbidity can still contain up to 1 million bacteria per ml
milky or very turbid cultures have close to a billion bacteria per ml
direct counts via microscopy
put on a slide and manually counted
still require 100,000 bacteria/ mL
