Virulence Factors Bacterial Colonization

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Virulence Factors Bacterial Colonization

• 1. adhere to host cells and resist physical
  removal
• 2. contact host cells
• 3. invade host cells
• 4. resist innate immune defenses such as
  phagocytosis
• 5. evade adaptive immune defenses
• 6. compete for iron and other nutrients

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Fastidious Bacteria

• The term fastidious refers to the difficulty of
  obtaining pure cultures of bacterium, due to
  special medium requirements, slow growth, etc.
  "Fastidious" fussy, meticulous.
• Characteristics
• 1. Bacilli
• 2. No flagellae (non-motile)
• 3. Most are Gm -, except for Clavibacter (Gm ) -
  causal agent for ratoon stunt disease (RSD) of
  sugarcane, bermudagrass stunt.
• 4. Sensitivity to high temperatures - hot air and
  water treatments can kill them. Ex RSD in
  sugarcane. Good control is hot water treatment of
  seed cane.

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FASTIDIOUS BACTERIA

• Two Basic Groups
• Phloem limited - Can't be grown in pure culture.
  Ex citrus greening

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FASTIDIOUS BACTERIA

• Two Basic Groups
• Phloem limited - Can't be grown in pure culture.
  Ex citrus greening
• 2. Xylem limited - can be grown in pure culture.
• Ex 1) Pierce's disease of grape - Xylella
  fastidiosa
• 2) Ratoon Stunting Disease (RSD) of sugarcane
  (Leifsonia xyli (formerly Clavibacter xyli subsp.
  xyli))

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Symptoms of RSD
General decline of ratooning (stubble crop)
Reddening of tissue
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Sugarcane and RSD
In August 2006, 10 of crop is harvested for
planting
Nitrogen application in Spring 07
Harvest in the Fall 2007
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Sugarcane and RSD
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Phytoplasmas and Spiroplasms

• Kingdom Prokaryotae cell membrane cell wall
• Bacteria
• Mollicutes (Phytoplasmas, Spiroplasmas)
  (3-layered) -

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Phytoplasmas

• Initially found to cause a group of diseases
  called "yellows" diseases.
• These diseases initially were thought to be
  caused by viruses because no fungi or bacteria
  were detected.
• Essentially they are small, wall-less bacteria.

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Characteristics of Phytoplasmas

• No cell wall, so they tend to be pleomorphic.
  They resemble mycoplasmas, which are known animal
  pathogens. The name "mycoplasma" means "fungus
  form".
• 2. Specialized three-layered cell membrane
  instead of a wall.
• 3. Extremely small - can be as small as 125 nm in
  diameter.
• 4. Can not be grown in pure culture
• (i.e., no completion of Koch's postulates).
• 5. Fragile, very sensitive to osmotic changes.

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Characteristics of Phytoplasmas

• 6. Gram -
• 7. Inhibited by antibiotics (i.e., tetracycline)
  that do not act by disrupting cell wall
  production (i.e., penicillin).
• 8. Transmitted by insects - leafhoppers (most
  important), plant hoppers. Piercing-sucking
  mouthparts! Phytoplasmas actually multiply within
  the salivary glands of insect vectors.
• Phytoplasmas are known to cause 200 plant
  diseases.
• Ex aster yellows, bunchy top of papaya, pear
  decline, lethal yellowing of palm.

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• Website - Phytoplasma Casts A Magic Spell
• www.apsnet.org/online/feature/poinsettia/top.html

The interactions between a phytoplasma and
poinsettia result in dwarfing and moderate
branching growth habit, which happens to be a
trait that poinsettia growers desire.
Technically, free-branching is a disease symptom
in poinsettias. But, like the virus associated
with classical color-breaking of tulip petals,
the poinsettia phytoplasma is beneficial to
growers, generating multi-flowered Christmas
showpieces and 325 million annually.
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Restricted-branching morphotype
Free-branching induced by phytoplasma
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Restricted-branching morphotype on left
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Spiroplasmas

• Similar in many regards to phytoplasmas, except
  that they can be cultured.
• Characteristics of Spiroplasmas
• 1. Small, helical organisms. They resemble a
  corkscrew.
• 2. The are motile. Can somehow use their
  corkscrew shape to propel themselves.

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Spiroplasmas

• Similar in many regards to phytoplasmas, except
  that they can be cultured.
• Characteristics of spiroplasmas
• 1. Small, helical organisms. They resemble a
  corkscrew.
• 2. The are motile. Can somehow use their
  corkscrew shape to propel themselves.
• 3. No cell wall.
• 4. Specialized three-layered membrane.
• 5. Exhibit sensitivity to antibiotics that is
  similar to that for phytoplasmas.
• Common spiroplasma-induced diseases Ex brittle
  root of horseradish, corn stunt

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Corn Stunt

• Symptoms are typical of phloem dysfunction
• Red leaves, green fruit, leaf dieback, bushy
  plants, stunting.
• Disease Cycle
• The spiroplasma overwinters within the adult
  leafhopper when the leafhoppers emerge from
  overwintering in early spring, they can be
  infective.
• Disease symptoms appear about 3 weeks
• after the corn is infected.

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Corn Stunt
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Brittle Root