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61 terms

Bacterial Growth & Metabolism, Microbiology

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True or false: Most bacterial pathogens can grow in the presence AND absence of oxygen.
True
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,
Environmental pH,
Salinity,
Temperature
What are prototrophs?
Bacteria that can synthesize all essential metabolites
What are auxotrophs?
Bacteria w/ acquired mutations that require them to obtain certain essential metabolites from environment
Name 2 common inhibitors of bacterial growth
Acid ph,
High salt
Name 1 bacterium resistant to acid pH. How does it overcome acid environments? What is the consequence?
Helicobacter pylori.

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?
Between 30C-37C
Mesophiles
Bacteria that can grow in extreme cold are called...
psychrophiles
Bacteria that can grow in extreme heat are called...
thermophiles
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
What proteins are used to bind & sequester iron?
Transferrin & lactoferrin
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?
Exponential phase
During which growth phase is it best to gram stain?
Exponential phase
During which growth phase do bacteria become somewhat refractive to antibiotic therapy?
Stationary phase
During which growth phase do Gram positive spore formers initiate sporulation?
Stationary phase
Individual, free-living backteria are called...
Planktonic bacteria
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
-Anti-phagocytic
-Often requires removal of infected implanted valve due to its adherent nature
Where are biofilms found?
-Implanted prostheses
-Dental plaque
-In-dwelling catheters
-Contact lenses
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
What are the products of glycolysis of sugars?
2 ATP + 1 pyruvate
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
Where does respiration occur?
On internal surface of cytoplasmic membrane
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.
True
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
Facultative enzymes lack which of the enzymes present in strict aerobes?
Catalase
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
What are the products of fermentation?
Lactic acid + Ethyl alcohol + CO2
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
True or false: Some bacteria can survive both inside and outside cells
True
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
What is the normal flora?
Commensal organisms resident or transient on human host
How do normal flora on the skin inhibit bacterial growth?
They produce fatty acids
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..
bacteremia
The vagina is prone to overgrowth by what type of bacteria?
Anaerobes
The vast majority of normal flora bacteria are located where?
Large bowel
What bacteria are normally present in the nose?
Staph aureus
Staph epidermidis
Diphtheroids
Streptococci
What bacteria are normally present in the teeth?
Streptococcus mutans
Bacteroides (anaerobes)
Fusobacterium
Stretococci
Actinomyces
What bacteria are normally present in the mouth?
Strep mitis and other streptococci
Trichomonas tenas
Candida
What bacteria are normally present in the throat?
Strep viridans
Strep pyogenes
Strep pneumoniae
Neisseria spp
Staph epidermidis
Haemophilus influenzae
What bacteria are normally present in urethra & vagina?
Staph epidermidis
Diphtheroids
Streptococci
Gram-neg rods
What bacteria are normally present on the skin?
Staph aureus
Staph epidermidis
Diphtheroids
Streptococci
Pseudomonas aeruginosa anaerobes
Candida
Trulopsis
Pityrosporum
What bacteria are normally present in large bowel?
Streptococci
Enterococci
Gram-neg rods (i.e. E. coli)
Anaerobes (i.e. Bacteroides & Clostridium spp)
Define pathogenesis
The mechanism of disease development
Define virulence
Expresses degrees of pathogenicity
Define colonization
Presence & multiplication of microorganisms 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

Ex: adhesion factors, capsules, endotoxins, exotoxins, siderophores