Oxidase Positive, Gram Negative Rods- Felton

Question 1

What are the general characteristics of Psuedomonas? What do they cause?

Answer 1

o Motile.
o Live in moist environments (sinks, mops, baths etc.) and has a strong assoc. w/ plant material.
o Oxidase positive.
o Obligate aerobes- Can grow by anaerobic respiration using nitrate as a terminal electron acceptor (instead of oxygen).
o Have a polysaccharide capsule (produces a mucoid appearance)
o Produce 2 water-soluble pigments:
1. Pyocyanin: bluish-green pigment.
2. Fluorescin: greenish-yellow pigment.
o Some give off a “grape-like” aroma (Ex. P aeruginosa).
o Opportunistic pathogen- Infects people w/ cystic fibrosis, severe burns, etc.
o Resistant to multiple antibiotics.
Cause: septicemia, endocarditis, pulmonary infections, ear infections, burn wound infections, UTIs, gastroenteritis, eye infections and MS infections.

Question 2

What are the virulence factors for Psuedomonas (8)?

Answer 2

1. Pili: allow attachment to respiratory epithelium.
2. Capsule: protection against phagocytosis as well as attach to epithelial surfaces of the trachea in cystic fibrosis patients.
3. Exotoxin A: irreversibly blocks protein synthesis (like diphtheria).Transfers ADP ribose to EF2.
4. Exoenzyme S: extracellular enzyme that has ADP ribosyltransferase activity. This enzyme is injected into the host by a Type III secretion system. Targets a small G protein (Ras) and subsequent ADP ribosylation of this protein results in collapse of the cytoskeleton.
5. Cytotoxin: pore-forming protein (aka leukocidin).
6. Extracellular proteases: elastase, alkaline protease help to spread the infection. Elastase breaks down elastic fibers in blood vessel walls, resulting in hemorrhage and necrosis. Alkaline protease degrades complement, IgG and IgM. Elastase and alkaline protease also inhibit neutrophil function.
7. Phospholipase C: breaks down phospholipids resulting in cell membrane and tissue destruction.
8. Endotoxin: LPS which can cause fever, shock, etc.

Question 3

What are the characteristics of Vibrionaceae?

Answer 3

o Facultative Gram- curved rods.
o Motile
o Oxidase positive.
o Grow well in alkaline media w/ simple nutrients.
Example: Vibrio cholera

Question 4

What are the characteristics of Vibrio cholera?

Answer 4

• Only serotype O1 and O139 cause epidemic cholera.
• Spread thru contaminated water or food (possibly in shellfish).
• Requires a high dose for infection.
• Produces a profuse, watery diarrhea w/ flecks of mucus (called “rice-water” stool) but no blood or inflammatory cells.
• Not invasive.
• Colonizes the surface of the brush-border cells of the SI and remains in the lumen.
• Entertoxin induces secretory diarrhea.
• Cholera cot: used to measure fluid losses and determine how much fluid for replacement and prevention of dehydration.

Question 5

What is the composition of Vibrio cholera Enterotoxin? What does it do?

Answer 5

Composed of A and 5 B subunits.
• B subuntis = binding of toxin to epithelial cells and delivery of A subunit.
• A subunit: active enzyme that causes ADP ribosylation of cellular G protein which regulates adenylate cyclase.
• Leads to overproduction of cAMP and derangement of ion transport.
• High cAMP → hypersecretion of Cl and bicarbondate into intestinal lumen → efflux of water.

Question 6

What are the characteristics of Vibrio parahaemolyticus? Symptoms?

Answer 6

• Halophilic marine vibrio that requires salt for growth.
• Free-living in coastal waters and estuaries.
• Gastroenteritis caused by these are from ingestion of raw or improperly cooked seafood (like oysters).
Symptoms: explosive watery diarrhea
• Pathogen strains produce Kanagawa hemolysin.

Question 7

What does Vibrio vulnificus cause?

Answer 7

• Causes progressive wound infections thru contaminated seawater or septicemia from ingestion of raw oysters.
• Pre-existing liver disease predisposes to septicemia.

Question 8

What are the characteristics of Campylobacter? What does Campylobacter jejuni cause? How is it transmitted? Symptoms?

Answer 8

• Slender Gram- curved rod.
• Oxidase-positive.
• Highly motile.
• Microaerophilic.
• Campylobacter jejuni = major cause of diarrheal disease in U.S.
• Found in lots of animals: poultry, dogs, cats, sheep and cattle.
• Infection thru contaminated milk, food or water.
Symptoms: bloody, muco-purulent diarrhea from both SI and LI w/ fever and abdominal cramps. (goes away in a week)

Question 9

What are the characteristics of Helicobacter? What does it produce to survive in the stomach? What does its exotoxin do?

Answer 9

• Strongly assoc. w/ gastritis, duodenitis and peptic and duodenal ulcers.
• Gram- and highly curved.
• Highly motile
• Oxidase positive
• Microaerophilic
• Produces urease which helps it to live in the low pH of the stomach.
• Found w/n the mucus layer overlying the gastric epithelium or adherent to its surface. Does not invade though.
• Produces an exotoxin called vacuolating cytotoxin (VacA) and a protein called CagA which causes proliferation of epithelial cells and predisposes to gastric cancer.
• Has a Type IV secretion system which injects effector proteins (CagA) into the gastric epithelial cells which induces production of IL-8.