QUESTION 1 (25 Marks) Hospitals in a rural suburb of Canada reported several pat

Question

QUESTION 1 (25 Marks) Hospitals in a rural suburb of Canada reported several patients with symptoms of bloody diarrhea. One patient had a low red blood cell count and renal failure The emergency room doctors ordered that samples be obtained from the patients. The samples were grown on the respective agar media. The microbiologist performed a Gram stain and observed pink rods. a. i. What is the causative agent for the above mentioned symptoms?( Mark) ii. State whether the organism is Gram positive or negative. ii. Give the reason for this particular Gram's reaction? (1 Mark) (3 Marks) b. Describe four features of the structure of the peptidoglycan layer of this microorganism. (4 Marks) Suggest a differential media that would facilitate the identification of this microorganism? Explain how the media works. c. (3 Marks) What antibiotic could the doctor prescribe to treat this disease? Describe its mode of action d. (3 Marks) e. The patients reported that the onset of symptoms occurred after the town barbeque where jerk chicken, festival and soda were served. What could have been the source of infection? 1 Mark) f. What two factors might have contributed to the growth of this organism? (3 Marks) g. How would the quantification of the microorganism from the sample mentioned in d be done using the standard plate count? (6 Marks)

Explanation / Answer

a.
1. The causative agent for the above-mentioned symptoms is Salmonella enteritidis.

2. Salmonella enteritidis is gram-negative bacteria.

3. When microbiologist performed the Gram -staining of the sample and found pink rod cells from the chicken sample. It is likely that the chicken was contaminated with salmonella enteritidis a gram-negative rod-shaped bacteria. It lacks the peptidoglycan layer which is present in gram-positive bacteria and hence it is unable to retain the crystal violet stain and appears pink in color.

b. Four features of the peptidoglycan layer are:
i) Peptidoglycan layer is composed of NAG - NAM complex. It provides rigidity to the cellular structure of the microorganism.
ii) A thick peptidoglycan layer around the cell membrane prevents the entry of various drugs used for killing the microorganism and hence it is protective in nature.
iii) It assists in the binary - fission reproduction of the organism.
iv) Chemical modification of the peptidoglycan layer determines the pathogenicity of salmonella.

c. A differential media that can be used for identification of Salmonella enteritidis is MacCONKEY'S Agar. This media prevents the growth of gram-positive bacteria due to the presence of crystal violet and bile salt in the medium and hence only gram-negative microorganism grows. The colonies of Salmonella can be identified by brick red in color and surrounded by a zone of precipitated bile. The color formation is due to fermentation of the lactose present in the medium and produces acids as end products.

d. Ampicillin can be administered to patients suffering from diarrhea. Ampicillin is a class of antibiotic derived from penicillin. It interferes with the ability of cell wall formation and makes holes in the bacterial cell wall. It drastically reduces the potency of the cell to thrive and leaks the cytoplasm of the cell thereby killing Salmonella entertidis.

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