3 microbial growth and metabolism Flashcards
bacterial growth:
how is it determined?
- increase in size adn numbers of bacterial cells (therefore increase in bacterial mass)
- determined in liquid culture to measure cell numbers or cell mass
4 distinct bacterial growth phases
- lag: adapt to new environ
- log: logarithmic increase in cell pop
- stationary: nutrient limitation, toxic products accumulate, pH change, reduced oxygen tensin
- death: highly variable
describe growth chart
- flat during lag
- positive slope, goes up during log
- flat during stationary
- negative slope, log decline, for death
log phase
fastest adn slowest
-growth rate, or doubling time, is determined by type of organism, nature of medium, env.factors\
10-12min in vibrios, c.perfringens
20-30min in e.coli, slamonella
24hours for tuberculosis
4 factors affecting bacterial growth
- Oxygen tension
- pH
- Temp
- Nutrition
oxygen requirements–4 types
- obligate aerobes: need 20% oxygen, resp.metab
- obligate anaerobes: resp.&fermentive metabolism
- facultative anaerobes: grow in either
- nanaerobes: grow with low O2 (6%)
oxygen toxicity….life developed in absence of? in presence of? what are 2 problems for life with oxygen adn aerobes?
- life developed in absence of oxygen
- life developed in presence of iron, sulfur, nitrogen
- iron-sulfur clusters: problem for life with oxygen
- iron: problem for aerobes
what enzyme in anaerobes becomes inactive in presence of oxygen
pyruvate ferrodoxin, an oxidoreductase (so it trasnfers electrons from teh reductant to the oxidant)
oxygen toxicity is because oxygen reacts with what to form what???
-oxygen reacts with electron transport components to form reactive products
O2 reacts to form H2O2 and O2-
H202 and O2- form OH.radical (toxic)
H2O2 adn O2- also produced by host cells
what enzymes inactive oxygen toxic byproducts? aka what enzymes to aerobes have?
- catalase
- peroxidase
(^both break down H2O2) - superoxide dismutase (SOD)
(^breaks down O2- and H)
fenton reaction, what plays a key role
H2O2 converted to OH.radical
iron plays key role in that
catalase reaction
peroxidase reaction
SOD reactione
- 2 H2O2 –> 2H2O + O2 (catalase)
- RH + H2O2 –> ROH + H2O (peroxidase)
- 2O2- + 2H –> H2O2 + O2 (SOD)
of catalase, peroxidase, adn superoxide dismutase, which do aerobes have? aerotolerant? anaerobes?
- aerobes have all 3
- aerotolerant organisms lack CATALSE (heme protein)
- anaerobes lack all 3 (SOD levels in aerotolerant anaerobes give correlation with degree of O2 sensitivity)
what enzyme to aerotolerant organisms lack? which enzyme is correlated to degree of sensitivity to O2?
they lack catalase
SOD levels correlate to O2 sensitivity
mesophiles, thermophiles, psycrophiles
- meso: bacteria of medical significance; 25-45C (fairly wide T range)
- thermo: high T
- psycro: low T
**there is overlap in terms of growth temps. see graph
pH of medically important bacteria?
pH of fungi?
pH of lactic acid bacteria?
6.5-7.5 medical importance
6-6.5 fungi
less than 4.5 streptococcus, lactic acid bacteria
what species grow in narrow pH range?
nisseria, bordetlla, pseudomonas
possible ecological pressures for caries (so that the very few pathogenic bacteria achieve numerical dominance over the healthy microflora needed for disease to occur)
sugar rich diet
low pH
low saliva flow
how can you target caries
target pathogen directly (antimicrobial/antiadhesion agents) & change environment, interfere with the ecological pressure that allowed the disease to occur
ecological plaque hypothesis
stress–> env change–> ecological shift–> disease
-caries is result of changes in env due to acid production from fermentation of dietary carbs, which selects for pathogenic bacteria
prevent disease by targeting pathogens and by changing env
all metabolic reactions require…?
energy + catalysts (enzymes, co-factors)
anabolism vs catabolism
anabolism = biosynthesis, use energy
catabolism = breakdown, ATP generation, generate energy adn reducing power
catabolism: 2 broad categories
- respiration: either aerobic (oxygen is terminal acceptor; requires ETC) or anaerobic (bacteria do this….other compound is terminal elec.acceptor; requires ETC)
- fermentation: organic compound is terminal electron acceptor
aerobic vs anaerobic respiration
both require ETC, but aerobic uses oxygen as final elec.acceptor adn anaerobic uses a different (inorganic) compound
4 steps in respiration and ATP made at each
- glycolysis (make 2 ATP)
- oxidative decarboxylation
- TCA/Krebs/CA cycle (2 more ATP)
- ETC (34 ATP)
net = 38 ATP produced/glucose
NAD+
nicotinamide adenine dinucleotide: coenzyme with ADP, ribose, and nicotinamide (from B3)
***reduces to NADH when it accpts H+ and 2e-
number ATP from NADH and FADH2
NADH – 3 ATP
FADH2 – 2 ATP
FAD
flavine adenine dinucleotide: coenzyme with ADP and riboflavin (vit B2)
reduces to FADH2 when it accepts 2H+ and 2e-
protein that generates ATP
ATP synthetase
4 shared metabolic pathways
- EMP = embden meyerhof parnas = GLYCOLYSIS (glucose to pyruvate)
- PPP = provides NADPH and ribose for n.tide synthesis (euk and prok)
- oxidative decarboxylation = pyruvate dehydrogenase decarboxylates pyruvate
- krebs = generate intermediates and elec.s for ETC
PPP
- pentose phosphate pathway
- in bacteria and euk
- provides NADPH and ribose needed for nucsleotide biosynthesis
- not much ATP generated here
glucose to G6P to ribulose6P to ribose5P
enzyme in oxidative decarboxylation
pyruvate dehydrogenase
EMP
aka glycolysis aka glycolytic pathway – breakdown glucose to pyruvate
3 unique metabolic pathways
- PFOR = pyruvate ferredoxin oxidoreductase to decarboxylate pyruvate
- Entner-Duodoroff: generate energy adn intermediates, in eubacteria not archaea
- glycoxylate: NOT used by euks; end products enter TCA, it metabolizes acetic acid and other fatty acids
entner-duodoroff pathway of fermentation net rxn
glucose –> 2 ethanol + 2CO2 + 1 ATP
anaerobic respiration differences
- TEA is not oxygen
- less efficient than aerobic; 30-34 ATPs per glucose (instead of 38)
fermentation
- when aerobes do not have oxygen
- only one step…GLYCOLYSIS, 2 NADHs produced reduce pyruvate to ferm.product
- can be done at same time as respiration
- not favorable (2ATPs, substrate level)
- different final products, most energy remains in fermentation products
lactic acid fermentation
pyruvate + NADH makes lactic acid + NAD+
enzyme = lactate DH
end product yield of Em-Meyerhof pathway for
- saccharomyces
- lactobacillus
- 2 ethanol, 2 Co2, 2 ATP
- 2 lactic acid, 2 ATP
both use fructose-1,6-diP aldolase
end product yeild of streptococcus in heterolactic pathway
1 of each: ethanol, lactic acid, co2, atp
uses phosphoketolase
end product yeild of Ent-Duo pathway for zymomonas
2 ethanol, 2 co2, 1 atp
uses KDPG aldolase
5 reasons why metabolism matters
- dental biofilm devo (need streptococcus 1st)
- dental clinical application - collect samples
- Fl- action
- abx choice
- devo of treatment
caries vs perio disease
- caries is on teeth
- perio disease is when it is in pocket
what bacterial species is first in biofilm devo
streptococcus
whayt bacterial species can adhere to basically any other bacteria
F. nucleatum
4 abx
- clindamycin: broad
- tetracycline: broad
- amoxicillin: broad (mainly G pos)
- Metronidazole: targets PFOR action — narrow, gets ANAEROBES
what abx targets anaerobic bacteria? how?
metronidazole
targets PFOR pathway
specimen collection from sites of infection
- collection of sterile sample (no contamination)
- protect anaerobes from oxygen
- needle aspiration (better survival of anaerobes, get larger quantity)
