03-18 Bacterial Growth and Metabolism Flashcards
(36 cards)
OBJECTIVE: What is the source and role of carbon?
role: in all molecules! and used for energy
source: glucose, other sugars, aa’s/peptides/prots, lipids, organic acids and alcohols (can be from other bact), nucleic acids
OBJECTIVE: What is the source and role of nitrogen?
role: needed for DNA and protein synth
source: aa’s, peptides/prots, nucleic acids, NH4+ and nitrate
OBJECTIVE: What is the source and role of sulfur?
role: proteins (think disulfide bonds)
source: Nucleic acids
OBJECTIVE: What is the role of nutrients vs. growth factors?
NUTRIENTS: are metabolized for energy or broken down and used as building blocks.
GROWTH FACTORS: are organic compounds a bacterium uses to make metabolites it cannot make on its own.
- -EXAMPLES: purines, pyrimidines, vitamines, a.a.’s, NAD+, heme, etc.
- -often substances readily available in host environment; bact “stopped making them” in effort to pare down the size of their genomes
- -fastidious bacteria require lots of growth factors
- -prototrophic bacteria synthesize everything they need to grow
OBJECTIVE: What physical requirements are needed for bacterial growth?
Correct temp - for pathogens usually = 37°C
Correct pH - most pathogens prefer our 7.4, but can withstand 6.0-8.0
Osmotic conditions - can withstand hypoosmotic conditions w/o bursting better than euk. cells b/c of cell wall
OBJECTIVE: Which physical requirements are needed for inhibition of bacterial growth?
Extremes in pH (directly inhibits growth AND increases heat susceptibility) and temperatures; increases in osmolarity
OBJECTIVE: How can you measure bacterial growth by colony formation? Describe method and calculation.
a.k.a. Viable (Plate) Counts b/c only measures viable cells
Use serial dilutions plated on agar:
- take 0.1mL of sample and inoculate 9.9mL or buffer (100 fold dilution or 10^x-2); then repeat process w/ inoculated buffer
- *want to have 30-300 colonies/plate
-calulation: (# colonies/# mL’s plated)/[dilution factor]
- given in units of CFUs/mL
- *CFU = colony-forming units
OBJECTIVE: What are other methods to measure bacterial growth?
- optically-measure turbidity by analyzing of light scattered using a spectrophotometer (limit of detection is ~1million bact/mL)
- measure amt of metab products (e.g. CO2, ATP)
- direct count under a microscope (though this gives a count of both alive and dead cells)
OBJECTIVE: What are the phases of the bacterial growth curve? How does the growth rate relate to dz?
- Lag - incr metab activity but no growth/division yet
- Log - a.k.a. exponential growth
- stationary - point at which cell death rate (due to decr nutrients, oxygen and/or growth factors; build-up of toxic metabolic substances; or, pH ∆) equals cell growth rate
- death - rate of cell death > growth; bacteria often ∆ shape (more difficult to ID)
generation time
time required for the microbial population to double; ranges from 20 mins (e.g. E. coli) to 20 hours (e.g. M. tb)
OBJECTIVE: What is the source and role of phosphorous?
role: membrane phospholipids, DNA (and ATP? not in notes)
OBJECTIVE: What is the source and role of iron?
role: co-factor for many enzymes, esp those involve w/ metabolism
source: acquired from host by secreting siderophores that bind scantly available host iron. this complex then undergoes receptor-mediated endocytosis
How do microbes metabolize nucleic acids?
secrete nucleases to break down RNA and DNA; can use them for their own NA synth or as sources of C, N and P
How do microbes acquire aa’s?
Can either uptake aa’s or secrete proteases to breakdown prots (too big by themselves) into aa’s.
–Proteases are a major virulence factor! (per slides)
What are phospholipases? What induces their production?
degrade host cell membranes and lung surfactant; up-regulated in low iron and low phosphorous conditions b/c when cells are lysed they release iron
–major virulence factor! (per slides)
Give an example of a human pathogen that grows temp lower than 37°C.
Mycobacterium leprae, thus the skin but no internal lesions
What is an example of a human pathogen that still grow well with refrigeration? What population is especially susceptible?
Listeria monocytogenes—>causes food poisoning and is a concern in pregnant women b/c can cross the placenta; from meat and animal products
How can the osmotic conditions of foods be altered to make them less susceptible to bacterial colonization?
increase sugar and/or salt concentration (i.e. salted fish, jelly)
What growth medium allows culture of ~90% of pathogens?
Blood agar
In what type of clinical sample should you find NO bacteria under normal conditions?
CSF
OBJECTIVE: Compare aerobic respiration with fermentation
fermentation: creates a net 2 ATP and recycles oxidizes NADH to NAD+ by turning pyruvate into ethanol or lactic acid.
–Only SUBSTRATE-LEVEL PHOSPHORYLATION
aerobic respiration: uses respiratory chain located in inner membrane to accept electrons from NADH creating proton gradient that drives ATP synthase; O2** is usually the terminal electron acceptor
–This is OXIDATIVE PHOSPHORYLATION
**NOTE: some bacteria can respire anaerobically but still do oxid. phos. by using other e- acceptors, e.g. NO3- reduced to N2
OBJECTIVE: How do fermentation products impact host-microbe interactions?
Lactic acid lowers pH and allows competition: e.g. beneficial Lactobacillus spp. in vagina prevents other microbes from growing, esp. Candia albicans which causes yeast infections
Butyric acid and butanol-acetone fermentation: clostridia; form butyric acid, acetic acid, H2 and CO2; wicked smelly but commensal intestinal species may use this pathway to protect us from E. Coli O157:H7
Propionic acid: ferments lactate to acetic acid, CO2 and propionic acid; Swiss cheese, acne
Mixed Acid Fermentation by eneteric microbes:
enterobacteriaceae (E. coli and Salmonella) use pyruvic acid to make acety-CoA and HCOOH (formic acid); formic acid—>CO2 and H2 if enzyme present—>gas gangrene
–end up with acetyl-CoA, formic acid, but also some ethanol, acetic acid and succinic acid thus “mixed”
2,3 butanediol and acetoin are made in addition to the mixed acids above by some non-fecal enterics
Ethanol fermentation: yeasts (Saccharomyces cerevisiae) and fungi (Candida albicans); CO2 appears as gas at low pH and non-gaseous carbonate at higher pH found in some tissue infections
Strickland Reaction: ferment using one amino acid to accept electrons from another a.a.; results in putrefactive derivatives of a.a.’s
OBJECTIVE: Explain the biochemical basis for obligates aerobes.
Absolutely need O2 b/c lack ferment enzymes; e.g. Mycobacterium tuberculosis which resides in lungs 1°ly
OBJECTIVE: Explain the biochemical basis for obligate anaerobes.
Most gain energy only from ferment b/c they do not have ECT.
–e.g. Bacteroides fragilis
Many contains flavins that create H2O2 which can create ROS and they lack the catalase and superoxide dismutase needed to protect themselves from these ROSs.
