1) What positive role might be played by the non-pathogenic streptococci normall
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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. When present in the oral biofilm in high numbers, certain beneficial streptococci which are called as comensals might be able to antagonize, or work against more cariogenic streptococci as suggested by clinical studies. Becker and his team determined the levels of several oral bacteria collected from healthy subjects and subjects with early childhood caries, a particularly virulent form of caries, and found a significant increase in the amount of S. mutans, collected from subjects with caries compared to healthy subjects. As expected, but they also observed an inverse relationship with S. sanguinis.These bacteria also H2O2 which is a protection against other pathogenic bacteria.
2. Antiseptic mouthwash should be avoided before this test as it will give wrong results. You should also make sure to check if you have been taking any antibiotics because this could affect the test results.
You will be asked you to open your mouth wide and tilt your head a little backward. If necessary, a tongue depressor may be used to get a better view of the back of your throat- the pharynx. the paramedic will then rub a sterile cotton swab across your tonsils, pharynx and any other sore areas for a few seconds. The sterile cotton swab will collect a sample of the secretions, loose tissue sediments if any being produced in the back of your throat. the swab is carefully removed taking care not to touch the swab anywhere in your oral cavity as the oral cavity will have different microflora altogether.
The test may cause momentary gagging because the back of the throat is a sensitive area, but it should not be painful.
The sample your doctor collects is then taken to a laboratory, where it is put on a petri plate with a suitable medium for bacterial growth and observation that allows any bacteria on it to grow. This process is called a culturing. Chemical tests are conducted on the cultured sample in order to determine the presence or absence of the required organisms and identity the presence of any harmful bacteria. It usually takes a couple of days to a week to culture the bacteria and obtain the results from this test.
3. When the physician suspecs a streptococcal infection, the sample is plated on blood agar so as to confirm the presence of that particular type. as streptococcus shows hemolysis when plated on blood agar, it is usually plated on it. the organism produces certain enzymes that are hemolytic in nature which forms a clear zone around the colony in blood agar confirming its presence.
5. When ?-hemolysis alpha hemolysis is seen, the agar right under the colony is discoloured, dark and greenish. Streptococcus pneumoniae and a group of oral streptococci display alpha hemolysis. This is sometimes referred as green hemolysis because of the color change in the agar. Other synonymous terms are incomplete hemolysis and partial hemolysis. Alpha hemolysis is caused by hydrogen peroxide produced by the bacterium, oxidizing hemoglobin to green methemoglobin.
Beta hemolysis ?-hemolysis, sometimes called a complete hemolysis, here a complete lysis of red cells surrounding the media around and under the colonies. The area appears lightened, creamy or yellow and transparent at times. Streptolysin, an exotoxin, is the enzyme produced by the bacteria which causes the complete lysis of red blood cells. There are two types of streptolysin: Streptolysin O (SLO) and streptolysin S (SLS). Streptolysin O is an oxygen-sensitive cytotoxin, secreted by most Group A streptococcus (GAS), interaction with cholesterol in the membrane of eukaryotic cells (mainly red and white blood cells, macrophages, and platelets), and usually results in ?-hemolysis under the surface of blood agar. Streptolysin S is an oxygen-stable cytotoxin also produced by most GAS strains which results in clearing on the surface of blood agar. SLS affects immune cells, including polymorphonuclear leukocytes and lymphocytes, and is thought to prevent the host immune system from clearing infection. Streptococcus pyogenes, or Group A beta-hemolytic Strep (GAS), displays beta hemolysis.
6. The coagulase test is mainly used to differentiate coagulase positive Staphylococcus aureus from coagulase negative staphylococci.
S.aureus produces two slightly different forms of coagulase (i.e., bound coagulase and free coagulase). Bound coagulase, otherwise known as "clumping factor", can be detected by carrying out a slide coagulase test, and free coagulase can be detected using a tube coagulase test.
staphylococci that do not clupm on addition of coagulase enzyme are negative for coagulase test.
7 and 8
Staphylococcus aureus shows high tolerance to high concentrations of sodium chloride in liquid medium. it is found that S. aureus grows at 37 C in Tryptose Phosphate Broth and mannitol salt agar that are saturated with sodium chloride. No difference was noticed between possibly pathogenic and nonpathogenic strains. Under the conditions of our tests, no changes in the original properties of S. aureus strains occurred.
In contrast, solutions of sodium chloride in distilled water were injurious to staphylococci and killed most of these organisms in 1 hr. Staphylococci were killed faster at 37 C than at room temperature in a solution of 0.85% sodium chloride in water.
9. a coagulase test can be performed in a test tube or on a glass slide where the presence of a coagulant ot clup or a clot is positive absence of a clot is negative. u only cannot compare as u do not have a positive control but the results remain the same and the clot is a obvious result that does not require a test at all.
10. The efficiency of the tube coagulase test, mannitol salt agar test can be markedly improved by a sequel testing of the isolates with Mannitol salt agar, DNase and Tube coagulase. There is no single phenotypic test (including tube coagulase) that can guarantee reliable results in the identification of Staphylococcus aureus. thus dnase positive confirms the presence of staphylococcus. dnase activity destroys DNA or denatures them.
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