LOs: 4

Question 1

Bacterial Growth Curve Phases

Answer 1

• Lag: initial phase after inoculation, when the bacteria are gearing up to grow (making more enzymes for growth, etc.)
• Exponential (Log): when bacteria are growing at a steady rate (“doubling time”)
• Stationary: bacteria use up nutrients and produce waste products, growth starts to slow
  o Before: Total = Viable (almost all bacteria in culture are alive)
  o After: Total > Viable

Question 2

How pathogens can overcome host irons equestration

Answer 2

The body uses iron-binding proteins (lactoferrin and transferrin) to restrict the availability of iron for pathogens

Pathogens fight back:

1) By producing their own iron-binding molecules (e.g. siderophores)
2) Some bacteria (e.g. the pathogenic Neisseria spp.) can bind human transferrin and lactoferrin to their surface and then use that bound iron

Question 3

Aerobes

Answer 3

Grow only in the presence of O2

Ex. Pseudomonas aeruginosa)

Question 4

Microaerophiles

Answer 4

A special group of aerobes requiring O2, but at lower concentrations than found in normal air

Ex. Campylobacter spp.

Question 5

Facultative anaerobes

Answer 5

Grow in either the presence or absence of O2 (e.g. E. coli)

Grow by fermentations in the absence of O2, but shift their metabolism to respiration in the presence of O2

More ATP is produced during respiration than fermentation, so growth is faster here

Ex. E. coli

Question 6

Aerotolerants

Answer 6

Grow in presence or absence of O2, but metabolism always uses fermentation

Ex. most Streptococcus spp.

Question 7

Strict anaerobes

Answer 7

Grow only in the absence of O2

Ex. Clostridium spp.

Question 8

Why some bacteria are anaerobic / Why anaerobes are sensitive to oxygen

Answer 8

Anaerobes often lack catalase (which breaks down toxic H2O2 formed after cells are exposed to air).

Anaerobes often lack superoxide dismutase (which detoxifies free radical forms of O2 that form after cells are exposed to air).

Anaerobes may have very sensitive enzymes that require a reduced environment.

Bottom line: anaerobes must be in a low redox (reduced environment) and O2
raises the redox potential.

The redox potential of healthy tissue is too high for anaerobes to grow.

Medical conditions that can lower tissue redox potential:

• Circulatory problems
• Tight orthopedic casts
• Co-presence of facultative anaerobes (which can consume oxygen) during an infection

Question 9

Body locations where anaerobes are normally found & Examples

Answer 9

Skin: Propionibacterium spp.

Mouth: Porphyromonas gingivalis

Vagina: Lactobacillus spp.; Prevotella bivia

Colon: Bacteroides fragilis

Question 10

Gram+ Anaerobes:
Sporeforming rods (1)

Answer 10

Clostridium spp.

Question 11

Gram+ Anaerobes:

Non-sporeforming rods (1)

Answer 11

Actinomyces spp.

Question 12

Gram+ Anaerobes:

Cocci (2)

Answer 12

Peptococcus spp.

Peptostreptococcus spp.

Question 13

Gram- Anaerobes:

Non-sporeforming rods (2)

Answer 13

Bacteriods-like group

Fusobacterium spp.

Question 14

Gram- Anaerobes:

Cocci (1)

Answer 14

Veillonella spp.

Question 15

Predisposing factors / medical conditions that can lead to anaerobic infections

Answer 15

Low tissue redox conditions from circulatory problems

Antibiotic therapy: can lead to Clostridium difficile infection

Bite wounds

Aspiration of mouth flora into the lungs

Spillage of intestinal contents into the peritoneal cavity due to perforation of the
GI tract

Question 16

Bacteriodes-like Bacteria:

Characteristics & Entry

Answer 16

Gram- anaerobic rods

Found as normal flora in colon, vagina, & mouth

Cause endogenous infections (breeching epithelium via surgery, wounds, ruptures, etc.)

Need low tissue redox for growth

Not contagious

Question 17

Bacteriodes-like Bacteria:

Virulence Factors

Answer 17

LPS is not endotoxic

Makes a capsule (antiphagocytic)

Some make an enterotoxin but not exotoxins

Not all are equally pathogenic (B. fragilis is most likely to cause disease)

Question 18

Bacteriodes-like Bacteria:

Diseases & Treatment

Answer 18

Disease near their normal flora colonization body site:

• Bacteroides fragilis: colon, abdominal infections that involve two stages: peritonitis and then (if untreated) abscess formation.
• Prevotella bivia: female genital tract, pelvic inflammatory disease and infertility.
• Prevotella melaninogenica and Porphyromonas gingivalis: mouth, respiratory tract infections (e.g., dental, chronic sinusitis, pulmonary infections).

Inflammation and abscess formation.

Can enter the bloodstream and cause bacteremia. Can be rapidly fatal.

Treatment for abscesses: surgical drainage and use of antibiotics effective against anaerobes (e.g., metronidazole).

Question 19

Histotoxic Clostridia:

Species & Characteristics

Answer 19

C. perfringens: most important

C. septicum: infections in pts w/ cancer of GI tract

Gram+ anaerobic spore-forming rods

Some normal GI flora, some in soil, some in both

Question 20

Histotoxic Clostridia:

Virulence Factors

Answer 20

Exotoxins: protein toxins made and secreted outside the cell.

α toxin: most important single toxin for C. perfringens, a lecithinase (phospholipase C) that disrupts mammalian plasma membranes.

Question 21

Histotoxic Clostridia:

Entry

Answer 21

Both endogenous & exogenous infections

1) Entry of cells or spores into wounds, ruptures, tumors, etc.
2) Need low tissue redox for growth

Question 22

Histotoxic Clostridia:

Diseases

Answer 22

1. Wound infections
   - Gas gangrene (clostridial myonecrosis): bacteria are present in muscle (low redox condition); toxins kill cells to form necrotic tissue (low redox), allowing progressive spread of infection. Toxins also enter circulation and damage distant organs. Rapidly fatal w/o treatment (if possible).
   - Anaerobic cellulitis: somewhat less serious, involves only cutaneous and subcutaneous tissue.
   - Simple wound infections: least serious, only involves cutaneous tissue.
2. Organ infections: e.g., uterine infections
3. Septicemia/bacteremias
4. C. perfringens type A food poisoning: 3rd most common food poisoning; not usually life-threatening, an enterotoxin causes diarrhea and abdominal cramps.

Question 23

Histotoxic Clostridia:

Treatment

Answer 23

Very difficult for gas gangrene

i) Removal of affected tissue by surgery (must be performed early in infection), often involves amputation. Antibiotics are in a supportive role.
ii) Hyperbaric O2 (?)
iii) Prevention: keep wounds clean.

Question 24

Bacterial Endospores:

Formed by…

Sporulation

Resistant to…

Sterilization

Why resistant

Answer 24

Bacillus (aerobic or facultative anaerobic) and Clostridium (anaerobic)

Survival response to a poor environment, not a reproductive strategy

• Heat
• Radiation
• Chemicals (some disinfectants)
• Drying

Aimed at killing bacterial endospores to kill all other life forms

• Low internal water
• Rich in DNA stabilizing proteins
• Lack metabolism (“suspended animation”)

Question 25

Diseases that can be transmitted by bacterial endospores

Answer 25

Anthrax: Bacillus anthracis Tetanus: Clostridium tetani Infections caused by the histotoxic clostridia (C. perfringens) Clostridium difficile

Question 26

Tetanus (C. tetani): Characteristics Virulence Factors Entry

Answer 26

Gram+ spore-forming anaerobic rod found in soils Tetanus neurotoxin inhibits release of inhibitory NTs --> uncontrolled muscle contractions --> lethal - Implantation of spores at a wound or during childbirth - Spore germinates into a new cell & makes tetanus toxin - Long incubation time while waiting for proper conditions to grow & germinate

Question 27

Tetanus (C. tetani): Disease Treatment Prevention

Answer 27

1) Toxin produced in wound and then migrates along nerves into CNS 2) Toxin blocks inhibitory neurotransmitter release; muscles are constantly stimulated. 3) Convulsive muscle contractions of voluntary muscles of the jaw (trismus, lockjaw), back, extremities. 4) Death results from respiratory failure. Treatment: very difficult, give tetanus antitoxin, muscle relaxants and assisted ventilation. Prevention: The disease itself does not confer immunity but immunization can be induced using tetanus toxoid.