1) What positive role might be played by the non-pathogenic streptococci normall
ID: 33792 • Letter: 1
Question
1) What positive role might be played by the non-pathogenic streptococci normally found in between the teeth and gingival crevice?
2) List the precautions that should be taken when obtaining a pharyngeal (throat) swab.
3) When strep throat is suspected, the physician often will recommend that a pharyngeal (throat) swab be taken and cultivated on blood agar. Why?
5) Explain how beta-hemolyis is distinguished from alpha-hemolyis.
6)What is the relationship of coagulase activity to the pathogenicity of Staphylococcus aureus?
7) Why are species of Staphylococcus often found as contaminants of ham and ham products?
8) Why is mannitol salt agar considered a selective as well as differential medium?
9) Suppose that a coagulase test is were performed without a control tube. How would this omission decrease the reliability of the test?
10) Explain how the ability to produce DNase would benefit the pathogenicty of S. aureus.
Explanation / Answer
1)
The non-pathogenic streptococci are act as commensals and exhibit the mutualism. Thus, they do not cause any harm to the humans, usually they are present in the mouth. For example, the common streptococci species found in gingival crevice are S. oralis, S. sanguis, and S. mitis.
Their main function is to protect the mouth from acid buildup and incoming pathogens. Thus, they partially maintain the pH of mouth and reduce the growth of disease causing oral pathogens.
2)
The specimen collector should wash hands before and after collection of the sample. When colleting sample, proper personal protective equipment should be worn. Before collection of sample, the patient could not administrate with any type of antibiotics.
5)
The most significant test for identification of streptococcus species is hemolysis. In alpha () hemolysis condition, dark green zones (1-3 mm) formed around the colonies; it is due to incomplete hemolysis by the production of hydrogen peroxide (H2O2).
In beta () hemolysis condition, the RBC (red blood cell) is completely degraded and form clear red zones on bacterial plate. This is due to an exotoxin called “streptolysin,” which is produced by the bacteria.
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