No other pathogenic bacteria were identified. The investigator became concerned
ID: 201896 • Letter: N
Question
No other pathogenic bacteria were identified. The investigator became concerned that this may be an infection with E. coll 0157:H7, a variant of E. cow that causes bloody diarrheas and very serious intestinal disease. This bacterium has acquired a toxin called Shiga Toxin (Stx), which is what enhances is virulence. The Shiga toxin gene was determined to actually be a virus gene 8) How did a virus gene get inside of E. colf? is the nam of this process? (3 points) A PCR test was done and showed the presence of the Stx gene. With the positive identification of Shiga toxin Escherichia coli (STEC), the investigator next wanted to determine how fast this bacterium was capable of growing. The investigator inoculated a small amount of the bacteria into a liquid culture, and at several time points, took 100 milcroliters out and counted the bacteria by plating it on a petri dish, allowing the colonies to form overnight, and then counting the colonies 9) Would this be a viable or direct cell count? (circle one- points) 10) The plate is to the left...rom the picture, determine the number of bacteria that were present in his 100 microliter sample (make sure to include the units). (3 points) cor After calculating all the data from the plates, the investigator constructed this growth curve below 11) Label the three phases of growth that are shown on the curve directly on the figure. (3 points) 10 0 10 4 0 Time (Hours) 12) Which growth curve phase is missing from the figure? (2 points)Explanation / Answer
8. The virus that infects the bacteria is called a bacteriophage. The virus which infects the bacterial cell and if the viral gene gets incorporated into the bacterial chromosome, it is called lysogenic phage or lambda phage. lysogenic phages are generally non-virulent but can become virulent and cause disease under certain conditions. Shiga toxin is such toxin produced by the viral genes that get incorporated into E.coli bacteria. Thus the E.coli cells produce Shiga toxin as it is expressed in E.coli.
The viral transfer of a gene from one bacterial cell to another bacterial cell through virus is called transduction.
9. It is a direct cell count. The growing bacteria in a petridish on an agar medium is in the form of colonies. Since the bacterial cells cannot be counted , counting the number of colonies that arise on an agar plate can calculate the concentration by multiplying the count by the volume spread on the plate.
number of bacterial cells in a single colony can be determined as each E.coli cell divides into two cells every 30 minutes. so a single cell can grow into a colony containing 107-108 cells in 12 hours. (224= 1.7 x 107)
10. In 100 micro litres sample : the number of bacteria on the plate are approximately in 36 colonies. 36 x 107 bacteria will be present.
11. The bacterial colony is showing a growth curve which is sigmoid growth curve or S-shaped growth curve. It consists of 3 phase.
i. lag phase : during whcih preparation for the growth is done
ii. lag phase or Exponential phase : during which rapid growth of the colony takes place
iii. Stationary phase : during which the growth stops and the line becomes parallel to the base line.
12. The deceleration phase after the exponential phase and before the stationary phase is not shown. During this phase the growth becomes slow.
24. Shiga toxin is a
i. Enterotoxin: because it is a toxin which is affecting the intestine. It causes diarhhoea.
ii. Exotoxin: Exotoxin is the toxin which is actively synthesised and secreted by the bacteria . The E.coli infected by the viral gene is synthesising and secreting the toxin.
iii. A/B toxin: It is an AB toxin since it is interfering with the cell function as in the diagram , it is shown that the protein synthesis is blocked which interferes with the cell function. AB toxins are the toxins which consists of two components.They are type III toxins because they interfere with cewll function. Compenent A is active portion and component B is binding portion and hence called AB toxin.
Antibiotics are not helpful in this situation because the antibiotics kill all the other useful bacteria that reside in the intestine which are helpful. So antimicrobials are avoided as the induce bacterial cell lysis and the release of stored toxins which are harmful.
26. STEC- Shiga toxin producing E. coli and humans show parasitic-host relationship. Because STEC are causing harm to the human , the host in which they are residing.
27. E.coli in humans gut has a symbiotic relationship. Symbiosis is a relationship between two living organisms with mutual benefit. E.coli draws the nourishment from the humans by residing in human gut. In turn humans get a benefit from E.coli as they protect humans from the pathogenic bacteria and help the body to digest the food.
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.