Staph and streph lab report

Document Type:Thesis

Subject Area:Biology

Document 1

Various tests were carried out to identify the specific strain of bacteria present in the sample. These are the gram stain test, the catalase test, the novobiocin test, the coagulase test, the blood agar plate test and the mannitol salt agar test. The tests were performed under standard conditions to yield correct results. From the results of the experiment, it was concluded that the strain of bacteria present in the sample was Staphylococcus aureus. This finding supported the hypothesis for the experiment. Introduction Streptococcus and staphylococcus are the two most important bacteria genuses that target humans. The two are coccus shaped and are Gram Positive. Staphylococci grow in clumps are catalase test positive. They also are part of the normal microbiota in humans. Staphylococcus aureus is coagulase test positive but there are coagulase-negative staphylococci that test negative with the coagulase test. The most important pathogen is Staphylococcus aureus which causes a number of pathogenic infections and illnesses that are toxin-mediated in its hosts. This pathogen has recently been developing antibiotic resistance to glycopeptides and methicillin. Save for Staphylococcus saprophyticus and Staphylococcus epidermidis, coagulase-negative staphylococci are usually non-pathogenic (Torok & Day, 2014). When Staphylococcus saprophyticus is opportunistic, it can cause epidermidis, urinary tract infections and skin lesions (Torok & Day, 2014). Staphylococcus aureus causes abscesses. The metabolic results of its pathogenicity are coagulase, leukocidins, DNase, lipase and Hemolysins (Foster, 1996). It is important to perform tests that have different results for different staphylococci because the different species of staphylococci that show different results with different tests have different clinical importance.

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For example, coagulase test-positive staphylococci like Staphylococcus aureus are responsible for many pathogenic illnesses and infections while coagulase test-negative staphylococci bacteria like Staphylococcus saprophyticus and Staphylococcus epidermidis tend to be non-pathogenic (Foster, 1996). On the other hand, streptococci grow in chains or pair (Torok & Day, 2014). Streptococci can be readily distinguished from staphylococci because of their appearance of Gram Stain and the fact that they have a negative catalase test result (Torok & Day, 2014). Streptococcus suis causes speticaemia and bacterial meningitis (Torok & Day, 2014). The genus streptococcus causes more infectious diseases than many other genuses. Streptococci are largely classified according to Hemolytic Activity and serological classifications. According to hemolytic activity, the bacteria are classified into Alpha, Beta and Gamma. According to Lancefield’s serological classifications, they have been divided into 20 groups with the first four groups A, B, C, and D being responsible for human infections.

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This test is important because it helps to distinguish the streptococci, which are catalase-negative, from the staphylococci, which are catalase-positive. Use of the Bacitracin will help to differentiate beta-hemolytic streptococcus. When this test is used, it is known that there is resistance when there is no zone of inhibition. On the other hand, the strain is known to be sensitive to Bacitracin when there is a zone of inhibition around the disk (Tankenshwar, 2013). The bile esculin test is used to identify catalase-negative bacteria. The preparation of a smear was done through the addition of a drop of a sample of the causative agent to a slide by the use of an inoculating loop that has been sterilized and dried by heat fixation (CMMB Department, 2016). This was followed by the addition of 2 drops of the primary stain (crystal violet reagent) and the slide allowed to sit for a minute.

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This was followed by rinsing of the slide with deionized water. The crystal violet was then decolorized using 95% ethanol which was added in drops until the crustal violet’s purple color faded completely away. This was followed by the addition of a few drops of the counterstain Safranin to the slide and then it was again allowed to rest for a minute. Mannitol Salt Agar Plate The sample was smeared using a sterilized inoculating loop along a vertical line on mannitol salt agar plate. This was followed by an incubation of the plate. Coagulase Test The sample was emulsified in a drop of water on a clean and grease glass slide with minimum spreading. A straight inoculating wire that had been flamed and cooled was dipped into the plasma that had been undiluted at room temperature.

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The adhering plasma species were then withdrawn and stirred into the bacteria specimen on the slide. Blood Agar Plate Blood agar changed color from opaque red to translucent pink. Colonies appeared on the plate. Halos appear around the colonies. Mannitol Salt Agar The entire plate changed color from pink to yellow. Coagulase Test Clumping occurred in 10 seconds in the coagulated plasma drop Novobiocin Test A zone of inhibition with a diameter of 38 mm was observed. Gram-positive bacteria with a thick peptidoglycan wall. Blood Agar Plate Blood agar changed color from opaque red to translucent pink. Colonies appeared on the plate. Halos appear around the colonies. Beta hemolysis takes place. This showed that catalase enzyme was present, which converted hydrogen peroxide into water and oxygen gas. The test narrowed the possible samples to only Staphylococcus epidermidis and Staphylococcus aureus, since all streptococcus bacteria test negative with the catalase test.

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The sample was then incubated using the blood agar plate. Colonies appeared on the plate, which indicated that the bacteria could use the materials present on the blood agar plate to grow (Table 2). There were also halos around the colonies which were pink and translucent which was an indicator that the bacteria was capable of beta hemolysis (CMMB Department, 2016). This is what makes it difficult to treat Staphylococcus aureus infections in humans (Gordon & Lowry, 2008). Staphylococcus aureus bacteria are arranged together in clusters that look like grapes that differ from the rod-shaped streptococci (Darenberg et al. The virulence factor that are linked to Staphylococcus aureus are associated with its adherence to the cells of the host, which enables it to avoid the immune system of the cell. This harms the host (Bien et al.

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Symptoms that are common in people suffering from Staphylococcus aureus are abscesses, boils and styes (Muder et al. Characterization of virulence factors of Staphylococcus aureus: novel function of known virulence factors that are implicated in activation of airway epithelial proinflammatory response.  Journal of pathogens, 2011. CMMB Department. Microbiology Lab Manual MCB 3020L, Fall 2016. University of South Florida. Norrby-Teglund, A. Differences in potency of intravenous polyspecific immunoglobulin G against streptococcal and staphylococcal superantigens: implications for therapy of toxic shock syndrome.  Clinical Infectious Diseases, 38(6), 836-842. Foster, T. Staphylococcus. R. Brennen, C. Rihs, J. D. Wagener, M. com/bacitracin-test-principle-procedure-expected-results-and- quality-control/ Török, M. E. Day, N. P. Staphylococcal and Streptococcal infections.

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