Bacterial Growth and Metabolism

Question 1

How do bacteria replicate?

Answer 1

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

Question 2

What does the growth rate of bacteria depend on?

Answer 2

The growth rate of a particular organism depends on the availability of nutrients, environmental pH, salinity, and temperature.

Question 3

What is the difference between phototrophs and auxotrophs?

Answer 3

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.

Question 4

T or F. Most bacteria are inhibited by BASIC pH

Answer 4

F. Most bacteria are inhibited by ACID pH. Low pH is an important feature of some tissues or organs in preventing infection

Question 5

How can species of bacteria such as Helicobacter pylori overcome acidic environments to live?

Answer 5

H. pylori secretes a urease to convert urea to ammonia and bicarbonate to establish infection in the gastric tract to cause ulcers.

Question 6

What is another inhibitor of bacterial growth?

Answer 6

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

Question 7

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).

Answer 7

mesophiles

Question 8

How is iron used during bacterial infection?

Answer 8

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.

Question 9

Most pathogens take between ___ and ___ minutes to replicate.

Answer 9

30 and 60

Question 10

How can bacterial growth in a liquid be measured?

Answer 10

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.

Question 11

What is happening during the lag phase of cell growth?

Answer 11

essentially no growth occurs. Instead, the bacteria are adapting to the new nutrient environment, reprogramming gene expression to meet the new needs.

Question 12

When are bacteria most susceptible to antibacterial therapy?

Answer 12

log phase

Question 13

Is there still cell growth during stationary phase?

Answer 13

Yes, but there is no NET increase in the number of viable cells.

Question 14

What are planktonic bacteria?

Answer 14

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.

Question 15

How do biofilms form?

Answer 15

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.

Question 16

How do biofilms prevent the use of antibiotics?

Answer 16

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

Question 17

Where are biofilms found in the body?

Answer 17

In addition to forming on implanted prostheses, biofilms are found in dental plaque, on in-dwelling catheters, and contact lenses.

Question 18

What is the downside of using aerobic respiration as a bacteria?

Answer 18

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.

Question 19

How do bacteria combat the formation of superoxide and hydrogen peroxide?

Answer 19

Strict aerobes produce three enzymes: superoxide dismutase, catalase, and peroxidase to diffuse the damage caused by the production of superoxide and hydrogen peroxide.

Question 20

Do facultative anaerobes use the same enzymes to combat the side effects of using oxygen for respiration?

Answer 20

They lack catalase, but they always synthesize superoxide dismutase and peroxidase

Question 21

Do strict anaerobes have the same enzymes?

Answer 21

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.

Question 22

How are patients with chronic granulomatous disease (CGD) affected?

Answer 22

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.

Question 23

T or F. Bacteria must synthesize folic acid rather than use environmental sources.

Answer 23

T. Folic acid is a source of nucleotides and methionine.

Question 24

What are obligate intracellular pathogens?

Answer 24

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.

Question 25

When can commensal organisms (good bacteria) cause disease?

Answer 25

(i) they spread to a normally sterile site,
(ii) they overgrow their typical niche as a potential pathogen, or
(iii) the host becomes immunocompromised, e.g., as a result of AIDS.

Commensals may spread from ruptured bowel, extracted teeth, or a nearby niche as in the case of perianal bacteria spreading to the upper urinary tract. Overgrowth can occur after antibiotic treatment reduces the numbers of residents and allows an antibiotic resistant species to expand, or when a change such as increased pH in the vagina occurs, favoring the growth of some species over others.

Question 26

T or F. Internal tissues and blood are normally sterile.

Answer 26

T. However, the skin, mouth, throat, and gastrointestinal tract, all accessible to the environment, are colonized by the normal flora

Question 27

The presence of bacteria in the blood is referred to as ____.

Answer 27

bacteremia

Question 28

What are the prominent skin flora?

Answer 28

Staphylococcus, Streptococcus, and Pseudomonas spp

Question 29

Where else is Staphylococcus found?

Answer 29

the nares

Question 30

What flora are found in the mouth?

Answer 30

Streptococci are normal components of the mouth flora, and perhaps surprisingly, anaerobes such as Bacteroides sp. are also common to the oral cavity, predominantly in the nooks and crannies of the gums

Question 31

What flora are found in the throat?

Answer 31

The throat is home to streptococci and some Neisseria sp.

Question 32

T or F. The lungs do not normally harbor bacteria

Answer 32

T. In part because of the effectiveness of lung cilia in combating colonization, but there is some evidence to indicate that humans are colonized at an early age by Pneumocystis jiroveci, a fungal-protozoan hybrid.

Question 33

What flora are found in the vagina?

Answer 33

The vagina and urethra are home to staphylococci, streptococci, and Gram negative rods, and the vagina is prone to overgrowth by anaerobes.

Question 34

What flora are found in the bowels?

Answer 34

The vast majority of normal flora bacteria reside in the large bowel, where streptococci, enterococci, Gram negative rods such as Escherichia coli, and anaerobes (Bacteroides and Clostridium spp.) can be found.

Question 35

What is pathogenesis?

Answer 35

the mechanism of disease development.

Question 36

What is virulence?

Answer 36

a term expressing degrees of pathogenicity.

Question 37

What is colonization?

Answer 37

the presence and multiplication of microorganisms without tissue invasion or damage.

Question 38

What is infection?

Answer 38

colonization that generally leads to disease.

Question 39

What is an epidemic?

Answer 39

a disease that rapidly affects many people in a fixed period of time.

Question 40

What is virulence?

Answer 40

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. Examples include adhesion factors, capsules, endotoxins, exotoxins, and siderophores.