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
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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
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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
what is an advantage of viable counts vs microscopy?
plate counts let you know how many live cells are in a sample, and measured as colony forming units
glyoxalate shunt
unique to microbes
2 enzymes (isocitrate lyase and malate synthase) shunt from isocitrate to malate in TCA
happens w/ a lot of acetyl-CoA (when cells are using lipids as a primary resource)
how is the electron acceptor different in microbes
we can only use oxygen
bacteria can use many different final acceptors (nitrogen, iron, sulfur, etc)
what can the proton gradient be used for in microbes?
ATP genetation
flagella motility
drug resistance (use gradient to create efflux)
what happens when ETC is unavailable?
fermentation- allows for regeneration of NAD and generation of ATP
generates less energy than respiration
lactic acid fermentation
pyruvate reduced by lactate dehydrogenase, regenerating NAD and lactate
fermentation to butyric acid
fermentation from pyruvate to butyric acid in gut, causes smell of feces and vomit
propioinic acid fermentation
associated w/ acne
yeast fermentation
pyruvate reduced to acetaldehyde, which is reduced by alcohol dehydrogenase to ethanol
differential acid production can show that different bacteria eat different things
different bacteria use different food sources and this info can be diagnostic
define: obligate aerobes
need O2, no alternative e receptors, no fermentation
facultative anaerobes
growth occurs w/ or w/o oxygen
aerobes and facultative anaerobes can detoxify reactice oxygen species
catalase (breaks down H2O2) and superoxide (breaks down superoxide, free radical oxygen) dismutase
obligate anerobes
cannot surivive w/ oxygen
cannot detoxify ROS
aerotolerant anaerobes
can tolerant oxygen, but do not use it for respiration
can survive ROS
micoaerophiles
require low concentrations of oxygen (5%)
environments found in the gut
