Bacterial Growth and Metabolism Flashcards
bacteria replicate by ___
binary fission
what is binary fission?
one cell divides to yield 2 daughter cells
the growth rate of a particular organism depends on:
availability of nutrients, environmental pH, salinity, and temperature
what are prototrophs?
bacteria that can synthesize all essential metabolites
what are autotrophs?
bacteria with acquired mutations that require them to obtain certain essential metabolites from the environment
most bacteria are inhibited by ___ pH and ___ salt
low (acid); high
why are human pathogens classified as mesophiles?
grow optimally bw 30-37C
other bacteria can grow in extreme cold of heat. what are these called?
psychrophiles and thermophiles
what nutrient stands out as one that greatly impacts the rate of cell division?
iron, important to growth and virulence
why is sequestration of free iron in blood and other body fluids by transferrin and lactoferrin (iron-binding proteins) significant?
defense against infection
Bacterial growth in a liquid (“broth”) culture can be measured by ___
growing aliquots of the culture on agar medium as the aliquots are taken at various times after broth inoculation
bacterial growth can also be followed by measuring the ___ of a liquid culture over time
turbidity; as the bacteria multiply, they cloud the broth which can be visibly seen and measured using a spectrophotometer
the bacterial growth curve includes what phases?
lag, exponential, stationary, decline/death phase
what is happening in the lag phase?
essentially no growth occurs; bacteria are adapting to new nutrient environment, reprogramming gene expression to meet new needs
what is happening in the exponential phase?
establish constant, optimal doubling times; bacteria experience maximal DNA and protein synthesis and are most acutely sensitive to antibiotic therapy; also best time to Gram stain organisms
- exponential growth leads to depletion of nutrients and accumulation of wastes. Metabolism is therefore greatly reduced and rate of cell division becomes equal to rate of cell death
what is happening in the stationary phase?
no net increase in number of viable cells (bacteria become somewhat refractive to antibiotic therapy and Gram positive spore
formers initiate sporulation)
what is happening in the decline phase?
nutrients deplete and waste increases, the rate of cell death exceeds the rate of cell division
what is a biofilm?
bacteria in a biofilm are encased in a protective carbohydrate matrix that is adhesive and only formed after a series of events requiring motility and adhesion of planktonic bacteria
why are biofilms significant?
bc of their prevalence, but also bc they are a source of recurrent infections and treatment failures; impairs antibiotic access to the residing bacteria, is anti-phagocytic, and bc of its adherent nature, often requires the removal of an infected implanted valve
what is the purpose of metabolism?
provide the energy and building blocks a cell needs to survive and replicate
describe oxidative respiration of aerobes and facultative anaerobes?
In the presence of oxygen, aerobes and facultative anaerobes funnel pyruvate through the citric acid cycle and oxygen serves as the final electron acceptor; produces 34 ATP
oxid. respiration occurs where?
internal face of cytoplasmic membrane
describe anaerobic respiration
In the absence of oxygen, an organic or inorganic compound other than oxygen serves as the final electron acceptor
is fermentation an efficient way of generating energy?
no
what is the major drawback of oxidative respiration?
produces hydrogen peroxide and superoxide anions (toxic to cell)
what enzymes do strict aerobes produce to diffuse the damage caused by production of ROS?
superoxide dismutase, catalase, and peroxidase
what enzymes do facultative anaerobes produce to diffuse the damage caused by production of ROS?
superoxide dismutase and peroxidase; will not always have catalase
what enzymes do strict anaerobes produce to diffuse the damage caused by production of ROS?
catalase and peroxidase, lack superoxide dismutase so die in presence of O2 due to accumulation of superoxide anions
why must bacteria synthesize folic acid?
source of nucleotides and methionine
obligate intracellular pathogens are dependent on the host cell for ____
nucleotide cofactors and ATP
can obligate intracellular pathogens be grown on synthetic medium in a lab?
no
how can normal flora (commensals) cause disease?
1) when spread to a normally sterile site
2) when they overgrow their typical niche as a potential pathogen
3) the host becomes immunocompromised
define pathogenesis
mechanism of disease development
define virulence
term expressing degrees of pathogenicity
define colonization
presence and multiplication of micro-organisms without tissue invasion or damage
define infection
colonization that generally leads to disease.
define epidemic
a disease that rapidly affects many people in a fixed period of time
define virulence factor
any number of products produced and often secreted by pathogens that allow the pathogen to invade and cause disease in a host and evade host defenses
