How do bacteria replicate?
Binary fission: 1 cell divides to yield 2 daughter cells. Those 2 daughter cells divides to produce 4 cells, etc.
1 Disrupt cell wall
2 Replicate bacterial genome & segregate to daughter cells
4 Establish new ends (septa) to cytoplasmic (& outer) membrane
Growth rate of an organism depends on 4 factors. What are they?
Availability of nutrients,
What are auxotrophs?
Bacteria w/ acquired mutations that require them to obtain certain essential metabolites from environment
Name 1 bacterium resistant to acid pH. How does it overcome acid environments? What is the consequence?
Secretes urease, which converts urea to NH3 & HCO3 to establish infection in gastric tract to cause ulcers
Human pathogens grow optimally at what temperature? This makes them fit which classification?
Bacteria that can grow in extreme heat are called...
Can be source of important heat resistant enzymes (i.e. DNA polymerase used for PCR)
Iron is a particularly important nutrient w/ regard to bacterial growth & virulence. Why?
Sequestration of free iron in blood & other body fluids is a significant defense against infection
How do bacteria counter iron limitation?
Secrete siderophores that chelate iron and are then actively transported to bacterial cell
Describe 2 laboratory methods that can be used to measure bacteria in culture
1 Grow aliquots of the culture on agar medium as aliquots are taken at various times after broth inoculation
2 Measure turbidity of liquid culture over time: As bacteria multiply, they cloud the broth which can be visibly seen & measured using spectrophotometer
Describe the stages of bacterial growth in culture
1 Lag phase: Essentially no growth occurs. Bacteria are adapting to environment & reprogramming gene expression to meet new needs
2 Exponential phase: Bacteria begin to replicate and establish constant, optimal doubling times
3 Stationary phase: No net increase in # of viable cells. Consequence of cell growth is depletion of nutrients & accumulation of waste. Metabolism greatly reduced such that rate of cell division = rate of cell death
4 Decline: As nutrients deplete and waste increases, rate of cell death > rate of cell division
During which growth phase do bacteria experience maximal DNA protein synthesis and are most acutely sensitive to antibiotic therapy?
During which growth phase do bacteria become somewhat refractive to antibiotic therapy?
What is a biofilm?
Encase bacteria in protective carbohydrate matrix that's adhesive and formed after series of events requiring motility and adhesion of planktonic bacteria
Why are biofilms a problem?
-80% of infections result from organization of bacteria in biofilm
-Source of recurrent infections & treatment failures
-Impairs antibiotic access to bacteria
-Often requires removal of infected implanted valve due to its adherent nature
Where are biofilms found?
Biofilms play a major role in what chronic disease?
Cystic fibrosis where Pseudomonas aeruginosa infection is common and results in formation of alginate biofilm
What is the purpose of metabolism?
To provide the energy and building blocks a cell needs to survive and replicate
After glycolysis, in the presence of oxygen, aerobes and facultative anaerobes will...
Undergo oxidative phosphorylation: Funnel pyruvate through CAC. Oxygen is final electron acceptor. Produce 34 ATP
After glycolysis, in the absence of oxygen, anaerobic bacteria will...
Undergo fermentation: Pyruvate is converted to various organic end products, CO2, or hydrogen. Electrons transferred directly to organic receptors
True or false: Fermentation is a very inefficient way to generate energy. For this reason, anaerobic growth is much slower than aerobic growth.
Oxidative respiration produces 2 toxic byproducts. 1. What are they? 2. What 3 enzymes do strict aerobes produce to diffuse the damage?
1 H2O2 & superoxide anions
2 Superoxide dismutase, catalase, peroxidase
Strict anaerobes lack which of the enzymes present in strict aerobes? What is the consequence?
Superoxide dismutase - killed in presence of oxygen due to accumulation of superoxide anions
True or false: Pathogenic anaerobes cannot survive even brief exposure to oxygen
False. They can survive brief exposure
Bacteria must folic acid rather than use environmental sources. Folic acid is a source of...
nucleotides & methionine
What 2 antimicrobials exploit the pathway used by bacteria to make folic acid?
Sulfonamide & trimethoprim
Give 2 examples of obligate intracellular pathogens. Can these pathogens be grown on synthetic media in the lab? Why or why not?
Rickettsia & Chlamydia
No, they are dependent on host cell for nucleotide cofactors & ATP. Culture requires animal cells in culture, so rarely part of diagnosis
How do gut normal flora inhibit bacterial colonization?
Produce toxins & waste that deter colonization
Also very dense (most dense in body), excluding new bacteria
How do vaginal normal flora inhibit bacterial colonization?
Produce acid environment (ex. lactobacilli)
Commensals can cause disease in what 3 situations?
1 They spread to a normally sterile site
2 They overgrow their typical niche as a potential pathogen
3 Host becomes immunocompromised
Give 2 examples of when bacterial overgrowth can occur
-After antibiotic treatment reduces # of residents and allows antibiotic resistant species to expand
-A change such as increased pH in vagina favors growth of some species over others
Internal tissues and blood are normally sterile. The presence of bacteria in the blood is referred to as..
What bacteria are normally present in the nose?
What bacteria are normally present in the teeth?
What bacteria are normally present in the mouth?
Strep mitis and other streptococci
What bacteria are normally present in the throat?
What bacteria are normally present in urethra & vagina?
What bacteria are normally present on the skin?
Pseudomonas aeruginosa anaerobes
What bacteria are normally present in large bowel?
Gram-neg rods (i.e. E. coli)
Anaerobes (i.e. Bacteroides & Clostridium spp)