Bacterial Growth and Metabolism Flashcards
How do bacteria replicate?
binary fission in which one cell divides to yield two daughter cells.
Fission requires the disruption of the peptidoglycan cell wall, replication of the bacterial genome and its segregation to the forming daughter cells, and the establishment of new ends (septa) to the cytoplasmic (and outer) membrane
What does the growth rate of bacteria depend on?
The growth rate of a particular organism depends on the availability of nutrients, environmental pH, salinity, and temperature.
What is the difference between phototrophs and auxotrophs?
Prototrophs are bacteria that can synthesize all essential metabolites, while auxotrophs have acquired mutations that require them to obtain certain essential metabolites from the environment.
T or F. Most bacteria are inhibited by BASIC pH
F. Most bacteria are inhibited by ACID pH. Low pH is an important feature of some tissues or organs in preventing infection
How can species of bacteria such as Helicobacter pylori overcome acidic environments to live?
H. pylori secretes a urease to convert urea to ammonia and bicarbonate to establish infection in the gastric tract to cause ulcers.
What is another inhibitor of bacterial growth?
high salt levels, but as with resistance to acid pH, some species are high salt-tolerant, and this feature is used in their diagnostic identification
Human pathogens are classified as ____ because they grow optimally between 30C and 37C, but other bacteria can grow in extreme cold (psychrophiles) or extreme heat (thermophiles).
mesophiles
How is iron used during bacterial infection?
The sequestration of free iron in blood and other body fluids by transferrin and lactoferrin (iron-binding proteins) is a significant defense against infection. To colonize the host, bacteria counter iron limitation by secreting siderophores which chelate iron and are then actively transported into the bacterial cell.
Most pathogens take between ___ and ___ minutes to replicate.
30 and 60
How can bacterial growth in a liquid be measured?
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. Alternatively, growth can be followed by measuring the turbidity of the liquid culture over time: as the bacteria multiply, they cloud the broth which can be visibly seen and measured using a spectrophotometer.
What is happening during the lag phase of cell growth?
essentially no growth occurs. Instead, the bacteria are adapting to the new nutrient environment, reprogramming gene expression to meet the new needs.
When are bacteria most susceptible to antibacterial therapy?
log phase
Is there still cell growth during stationary phase?
Yes, but there is no NET increase in the number of viable cells.
What are planktonic bacteria?
free-living bacteria, that are characterized by growth conforming to a standard lag/log growth curve. While this is typical of the laboratory growth of bacteria, it is estimated that 80% of infections result in the organization of bacteria into a biofilm.
How do biofilms form?
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
Biofilms are significant because of their prevalence, but also because they are a source of recurrent infections and treatment failures.
How do biofilms prevent the use of antibiotics?
The biofilm impairs antibiotic access to the residing bacteria, is anti-phagocytic, and because of its adherent nature, often requires the removal of an infected implanted valve
Where are biofilms found in the body?
In addition to forming on implanted prostheses, biofilms are found in dental plaque, on in-dwelling catheters, and contact lenses.
What is the downside of using aerobic respiration as a bacteria?
Although oxidative respiration is more efficient at producing energy for the cell, it comes at a price. Respiration in the presence of oxygen produces hydrogen peroxide and superoxide anions, two toxic products for the cell.
How do bacteria combat the formation of superoxide and hydrogen peroxide?
Strict aerobes produce three enzymes: superoxide dismutase, catalase, and peroxidase to diffuse the damage caused by the production of superoxide and hydrogen peroxide.
Do facultative anaerobes use the same enzymes to combat the side effects of using oxygen for respiration?
They lack catalase, but they always synthesize superoxide dismutase and peroxidase
Do strict anaerobes have the same enzymes?
In contrast, strict anaerobes lack superoxide dismutase and therefore are killed in the
presence of oxygen due to the accumulation of superoxide anions. Nonetheless, pathogenic anaerobes can survive brief exposure to oxygen.
How are patients with chronic granulomatous disease (CGD) affected?
The presence or absence of catalase has another consequence for bacteria. Patients with chronic granulomatous disease (CGD) lack NADPH oxidase in their neutrophils. Consequently, the neutrophils fail to produce an oxidative “burst” that would normally kill phagocytosed bacteria. Because normal metabolism will provide some hydrogen peroxide inside cells, catalase-negative bacteria such as streptococci can still be killed by the defective neutrophils. However, catalase-positive bacteria such as staphylococci can overcome the basal levels of peroxide to survive and cause recurrent infections. This would not occur in a normal neutrophil where the oxidative burst would be sufficient to kill even catalase-positive bacteria.
T or F. Bacteria must synthesize folic acid rather than use environmental sources.
T. Folic acid is a source of nucleotides and methionine.
What are obligate intracellular pathogens?
Bacteria that can only replicate inside of host cells. Rickettsia and Chlamydia spp. are prime examples of obligate intracellular pathogens.
These bacteria are dependent on the host cell for nucleotide cofactors and ATP, and cannot be grown on synthetic media in the laboratory. Consequently, culture of these bacteria requires specialized laboratories growing animal cells in culture and is rarely a part of the diagnosis.
