Microbio 3-19 growth metabolism Flashcards
How does an infection occur?
disruption of physical barriers (ie surgical sites/burns), immune dysfunction, or perturbations of the immune system
What is the generation time?
time required for the population to double
What is the generation time for a typical bacterium?
It varies depending on the organism. It can be as short as 20 minutes or as long as 20 hours, but many pathogens have generation times of less than 30 minutes
What limits the growth of a pathogen? (5)
1) exhausted nutrient supplies or key resources. 2) Accumulation of toxic metabolic products. 3) Antibiotics from neighboring microbes/humans. 4) Immune system. 5) Environmental conditions
What are the major nutrients required for bacterial growth? 5)
Carbon, Nitrogen, Phosphorus, Sulfur, Iron (C-SPIN)
Nutrient sources serve 2 major functions. What are they?
1) energy source. 2) source of carbon for the synthesis of all cellular components. Ex: in the presence of O2, many bacteria can oxidize ~50% of glucose -> CO2+H2O, which produces enough energy/ATP to convert the remaining 50% of the glucose to biomass (cellular components)
What are 5 potential host sources of C, N, and S that pathogens use? What are 2 additional sources of N?
1) amino acids 2) peptides 3) proteins 4) nucleotides 5) phospholipids. Ammonia (NH4+) and nitrate from the diet or NO (produced by the immune response) are also possible nitrogen sources
T/F The carbon sources that bacteria use can be diagnostic.
True.
Neisseria gonorrohoeae and Neisseria meningititidis can be distinguised based on the carbon sources that they use. What are they and how are they different between the two strains?
Neisseria gonorrhoeae can grow in glucose but NOT maltose, whereas Neisseria meningititidis can grow in glucose & maltose.
What is the significance of the proteases that bacteria secrete?
a.a. and peptides can be taken up by bacteria, but proteins cannot because they are too big. Thus proteases serve to degrade the proteins into smaller fragments (a.a. and peptides) that the bacterium can take up and use for C, N, and P sources.
What is the significance of the nucleases (RNAse, DNase) that bacteria secrete?
to break down available RNA and DNA so that they can be used as C, N, and P sources, or for their own DNA/RNA synthesis
What is an inducer of nucleases (RNAse, DNase) production in pathogens?
P sources
What is the significance of the phospholipases that bacteria secrete?
it acts to liberate phospholipids from host cell membranes or lung surfactant, which then provides microbes with C, N, and P sources.
What is an inducer of phospholipase production in pathogens?
low phosphorus or low iron levels
Host cell lysis by phospholipase activity yields this:
Iron (Fe)
Iron liberated from host cell lysis is used for:
generation of ATP via the ETC
Describe how iron (Fe) sources are “shared” between the host and the pathogen.
The host makes Fe-binding proteins that make iron unavailable to microbial invaders. However, the microbial invaders produces siderophores (iron cheloators) that can extract iron from host reserves.
Define virulence determinants (virulence factors)
mechanisms that a pathogen employs to establish itself and produce the subsequent disease
What are examples of virulence determinants that pathogens use?
proteases, nucleases, phospholipases, siderophores
What are siderophores?
iron chelators that bacteria produce that has a very high affinity for Fe.
What happens if the pathogen cannot secrete siderophores?
Since serve to sequester Fe for the pathogen to use (in the production of ATP), the pathogen becomes avirulent if it cannot produce siderophores
What are extracellular and intracellular examples of siderophores that deliver Fe from the host to the pathogen?
Extracellular: transferrin, lactoferrin. Intracellular: Ferritin, hemoproteins, phopholipase (causes cell lysis and subsequent release of Fe). (think: E-TL; I-PFH)
What are growth factors (in the pathogen world)?
organic compounds that are used to make metabolites that the bacterium cannot synthesize themselves. NOTE: they are not metabolized to supply energy!
Different organisms require different growth factors. What is the difference between a fastidious bacterium and a prototrophic bacteria?
Fastidious: require many growth factors to grow and are usually commensal bacteria that live in the GI tract where there is a continuous supply of nutrients. Prototrophic: can synthesize everything it needs to grow.
What is the evolutionary advantage of fastidious bacterium?
they don’t have to synthesize anything themselves – they can just get it from the host.
Haemophilus requires these two factors in order to grow.
they can only grow on medium containing heme and NAD+
What are 3 environmental factors that affect the growth rate (generation times) of a pathogen?
1) temperature. 2) pH. 3) osmotic conditions
What is the optimal temperature for most pathogens?
37C
What is a pathogen that can grow at a reduced body temperature?
Micobacterium leprae - optimal growth at reduced body temperatures (and poorly at 37C), which is why the lesions are present on the skin and not on internal organs
What is a pathogen that can grow at an elevated temperature (>37C)?
Legionella
What is a pathogen that can grow at an low temperature (>4C)?
listeria (a causative agent of food poisoning)
What is the optimal pH for most pathogens?
pH 6-8, optimum 7.4
How does a lower pH affect the growth rate of a bacterium?
low pH can inhibit the growth of unwanted bacterium or by reducing the heat resistance of the microbe (such that they become more sensitive to heat)
How can bacteria affect their local pH?
by producing acid or releasing ammonia (from metabolic products) to make the growing conditions more favorable.
How does the production of urease by the bacterium make their environment more favorable? What is an example of a bacteria that does this?
Urease converts urea -> NH3, which raises the local pH to make the local growing conditions more favorable. This mechanism is employed by Helicobacter (whih causes gastric ulcers and cancers) to raise the local pH in the stomach to make it more hospitable for them
How does the osmotic gradient affect the growth rate of a bacterium? What is an exception to this?
very high salt/sugar concentrations can inhibit the growth of many pathogens. Staph Aureus is salt resistant and can cause food poisoning associated with salty foods (ie hams) if not properly handled.
What is a bacterium that is generally associated with food poisoning from ingesting salty foods (ie hams)
staph aureus
Why is it that most bacteria do not need to regulate their own internal osmolarity with exact precision?
because they are enclosed by a cell wall that is capable of withstanding a considerable internal osmotic pressure.
What are the components of the common growth medium?
peptone with glucose added
What is peptone?
peptic digest of meat containing peptides and a.a.
What is the purpose of peptone and glucose in the common growth medium?
serve as carbon sources and additional sources of energy
T/F Blood agar supports the growth of _____% of pathogens
90%.
What is the purpose of using a solid medium? (3)
1) obtain pure cultures of bacteria. 2) observe colony morphology. 3) quantification
Why is the measurement of bacteria important in clinical settings? (2)
1) to determine if there is an infection. 2) antibiotic susceptibility testing needs to be done with cultures at a known density to be accurate.
Which clinical samples should you expect 0 bacteria?
CSF
T/F Urine is sterile and therefore does not contain any bacteria.
Generally true, but it is expected to find some organisms, so levels matter.
What are 4 ways that you can measure bacteria?
1) optical measurements using a spectrophotometer. 2) determination of metabolic activity (using dyes that measure ETC activity, redox activity, and ATP levels). 3) direct measure of cell # using a counting chamber. 4) viable/plate counts by measuring CFU
What does the CFU indicate?
number of viable bacterial cells in a sample.
