Kosh's Postulates

1. Show how each of Koch’s Postulates were proven or disproven.
The first step was successful in that we isolated the ‘soft rot’ from our diseased carrot and grew a pure culture on a N/A plate. Koch’s Postulate’s was disproven because we didn’t grow any ‘soft rot’ on our carrots when we inoculated them with the disease and therefore couldn’t isolate any pure colonies.

2. What causes soft rot in carrots? Explain.
A bacteria called, Erwinia carotovora, is responsible for ‘soft rot’ in carrots. It is a gram negative bacillus, plant pathogen that invades plants and causes decay. It weakens the cells, destroys pectin and degrades cellulose (Wikipedia).

3. Why will the addition of water speed the disease process?
Water allows the diffusion of the diseased particles to migrate faster throughout the carrot/infected specimen. Also, due to waters osmosis effects, water probably went into the intercellular spaces of the carrot and caused a hyper or hypotonic effect; which results in cell death.

4. When would it be inappropriate to apply conventional Koch’s Postulates to an infectious disease?
It would be inappropriate to use Koch’s Postulates when the infectious disease is human based. If you find a disease in a human, it would be unethical to isolate it and then inject a healthy human in order to see if the disease is in fact what you thought. I would assume that if you did isolate a pathogen from a human and tried to do Koch’s Postulates, but with an animal being the recipient of the disease, the data would be inefficient because a different subject was used and the pathogen would not infect the animal in the same way as a human.

5. What are Molecular Koch’s Postulates?
Identify gene (or gene product) responsible for virulence determinant
Show gene present in strains of bacteria that cause the disease
Not present in avirulent strains
Disrupting the gene reduces virulence
Introduction of cloned gene into avirulent strain confers virulence.
The gene is expressed in vivo
Specific immune response to gene protects (http://www.microbiologybytes.com/introduction/b2.htm)
6. Give a specific application of Molecular Koch’s Postulates.
Wasn’t really sure what you wanted here, so I found a summary of when someone used Molecular Koch’s Postulates specifically.

“Salmonella pathogenicity island 1 (SPI1) encodes the components of a type-III-secretion apparatus, which allows the delivery of bacterial effector proteins to host cells. The effector genes in SPI1 are primarily expressed during the initial gastrointestinal phase of the infection. Mutations in SPI1 are attenuated for oral infection; however, SPI1 is not necessary for the systemic phase of the infection because SPI1 mutants are not attenuated when they are administered in mice intraperitoneally, which bypasses the gastrointestinal phase of the infection. In macrophages, one SPI1-encoded effector protein, SipB, induces host-cell death through its interaction with a host cysteine protease, caspase-1. Caspase-1 is a proinflammatory enzyme, and its activation by SipB not only induces cell death, but also leads to caspase-1 cleavage of the inactive precursors of interleukin (IL)-1 and IL-18 to generate the mature proinflammatory forms. Therefore, Salmonella kills the phagocytic cells it encounters but, paradoxically, at the same time 'deliberately' induces an inflammatory response that is destined to bring even more phagocytic cells into its immediate vicinity. A direct role for SipB in SPI1-mediated cell death is supported by a number of observations. However, single mutations in the sipB gene do not lead simply to the loss of the ability to induce caspase-1 and cell death, but also to a loss of all SPI1 functions — presumably because disruption of the SipB protein leads to disruption of the mechanism by which effector molecules are translocated to host cells. So, although SipB, has been proposed to be the main activator for caspase-1 during in vivo infection, it has been difficult to directly address this possibility owing to the multiple roles of SipB, in addition to directly activating caspase-1 (Molecular Koch's postulates applied to bacterial pathogenicity — a personal recollection 15 years later).”
7. Eighty-one patients became ill and 14 died in an outbreak at St. Elizabeth’s Hospital, Washington, D.C., in 1965. Epidemiologic evidence suggested a link between infection and wind-blown dust from excavations on hospital grounds. In 1968, 144 cases of self-limited illness occurred in employees at the health department in Pontiac, MI. Investigations at that time demonstrated that the etiologic agent was present in the condenser of a malfunctioning air-conditioning system. In 1974, at least 20 persons attending a convention at the Bellevue Stratford Hotel in Philadelphia developed pneumonia, and two died. In 1976, 182 people became ill and 29 died at another convention at the Bellevue Stratford hotel. Explain, in detail, how you would identify the causative agent of these outbreaks by applying Koch’s Postulates.

I would isolate the disease in all the people that were infected as well as the people who died to see if the organism was found in abundance; this would be done by growing the organism that is found in the ill people and grow it in a pure culture. This organism would be labeled and verified. In order to identify the causative agent, with this organism identified, it would need to be compared to the other samples and then have tests run to determine where the pathogen grows and what the likely culprit was that gave it to these people; something in the dust or self-employed disease. You could also inoculate a breed of animal and see what happens to the animal; grow a pure culture from the sampled animal and see if the same organism grows.