Bacterial Growth and Metabolism Flashcards
- Know conditions that affect bacterial growth rate - Describe a typical bacterial growth curve - Define siderophore and bacterial biofilm - Distinguish aerobic from anaerobic growth - Define normal flora and recall benefits and hazards of colonization - Recall principle of normal flora of various tissues - Define Key terms associated with infectious disease
How do bacteria replicate
binary fission
In binary fission, what happens in the cell?
- disruption of peptidoglycan cell wall
- replication of bacterial genome
- segregation to form daughter cells
- establishment of new ends (septa) to cytoplasmic (outer) membrane
Growth rate of bacteria depends on?
- nutrients available
- pH
- salinity (salt content)
- temperature
Prototroph can ____________?
synthesize all essential metabolites
What do auxotroph need for cell survival?
need to obtain essential metabolites from the environment. (cannot synthesize their own because they have acquired mutations in synthesizing essential metabolites.
Normally, Acidic or basic pH inhibits bacterial growth?
Acidic, low pH in certain tissues and organs prevent growth
What bacteria can overcome the acidic environment?
How?
Helicobacter pylori, H. pylori
secrete urease that converts urea to ammonia and bicarbonate –> establish infection in the gastric tract to cause ulcers
High or low salt concentration in the environment inhibits growth?
High! there are some that are resistant too.
Human pathogens are classified as ?
meophiles, because they grow optimally between 30 -37 degree Celsius.
What nutrient impacts the rate of cell division?
Iron, it is important to growth and virulence (capability to cause disease)
How does the human body sequester free iron in the blood?
by transferin and lactoferrin, iron-binding proteins –> significant defense against infection
What must happen for bacteria to colonize the host?
counter the iron limitations
How do bacteria counter iron limitations?
secreting siderophores which chelate irons and then ACTIVELY transport into the cell
How are bacteria measured in liquid culture?
Growing aliquot(portion of total ) of the culture on agar medium as the aliquots are taken at various times after broth inoculation.
What is an alternative way to measure growth of bacteria ?
Measure turbidity (cloudiness) of the liquid culture over time. As bacteria multiply, they cloud the broth and measured using spectrophotometer.
Why is there no growth immediately after inoculation of the liquid culture?
LAG PHASE
What happens in lag phase?
bacteria are adapting to new nutrient environment, reprogramming gene expression.
Bacteria replication is constant and at an optimal doubling times in what phase
Exponential Phase
What happens in the exponential phase in the cell?
maximal DNA and protein synthesis
What phase is most sensitive to antibiotic therapy?
exponential (logarithmic phase)
When is a good time to gram stain organism?
exponential phase
What is a consequence of exponential growth?
depletion of nutrients and accumulation of wastes
Describe the stationary phase
metabolism is reduced, rate of cell division is equal to the rate of cell death. Thus, no net increase in the number of viable cells.
When do gram positive bacteria initiate sporulation?
stationary phase
Describe the decline (death) phase?
rate of cell death exceeds the rate of cell division due to depletion of nutrients and accumulation of waste
80% of infections results from bacteria organizing to form ?
biofilm
What is biofilm?
a protective carbohydrate matrix, formed by events of motility and adhesion of bacteria
Why is biofilm important ?
they are a source of recurrent infections and treatment failures. It impairs antibiotic access, anti-phagocytic, and requires removal of the infective implant b/c of its adherent nature.
Where can biofilm be found?
dental plaques, in-dwelling catheters, and contact lens
What is the purpose of metabolism?
To provide energy and building blocks for cell survival and division.
What kind of bacteria can use oxygen?
facultative anaerobes and aerobic bacteria
How many ATP can be produced?
34
In absent of oxygen, what can occur in facultative anaerobes?
anaerobic respiration: oxidation of an organic or inorganic compound other than oxygen.
Strict (obligate) anaerobes use
fermentation to generate energy and metabolite
During fermentation, pyruvate –>
organic compounds like acetic acid, butyric acid, lactic acid, CO2. Inefficient way to generate energy
Which grows slower: anaerobic growth or aerobic growth?
anaerobic growth
Consequence of respiration?
produce H2O2 and superoxides
Strict (obligate) aerobes produce 3 enzymes
superoxide dismutase, catalase, peroxidase
Facultative anaerobes may lack which of the 3 enzymes?
catalase
Why is O2 toxic to strict (obligate) anaerobes?
Lack superoxide dismutase, thus accumulation of superoxide anions.
Why do bacteria must synthesize folic acid rather than use it from the environment?
B/c it is a source of nucleotides and methionine.
What can be a key aspect of pathogenesis and spread of bacteria?
intracellular survival
What are obligate intracellular pathogens?
Bacteria that can only replicate inside of host cells.
What are some features of obligate intracellular pathogens?
they are dependent on the host cell for nucleotide cofactors and ATP
What are some benefits of normal flora?
inhibit growth of new bacteria by several ways: production of FA in the skin, toxins and waste in the gut, occupy space in the gut, produce acid in the vaginal area
What are some benefits of gut normal flora?
produce toxins and waste that deter other bacteria
How can normal flora be bad?
When they spread to a normally sterile site, overgrow their niche, become immunocompromised
(internal tissue and blood are normally sterile sites)
What are bacteria in the blood called?
bacteremia
