Bacterial Growth & Metabolism, Microbiology

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True or false: Most bacterial pathogens can grow in the presence AND absence of oxygen.


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,

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

Bacteria that can grow in extreme cold are called...


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

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
-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.


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?


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


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..


The vagina is prone to overgrowth by what type of bacteria?


The vast majority of normal flora bacteria are located where?

Large bowel

What bacteria are normally present in the nose?

Staph aureus
Staph epidermidis

What bacteria are normally present in the teeth?

Streptococcus mutans
Bacteroides (anaerobes)

What bacteria are normally present in the mouth?

Strep mitis and other streptococci
Trichomonas tenas

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
Gram-neg rods

What bacteria are normally present on the skin?

Staph aureus
Staph epidermidis
Pseudomonas aeruginosa anaerobes

What bacteria are normally present in large bowel?

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

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