Gram Positive Pathogenic Cocci

Topics: Bacteria, Microbiology, Pathogen Pages: 2 (670 words) Published: April 9, 2012
Judson Cotterman III
Section 185-35L
Assignment #3 Gram-positive Pathogenic Cocci

My original hypothesis for the individually collected throat culture on Blood Agar Plates, that it would show a mixture of alpha, beta, and gamma hemolysis, was based on the results of the class control samples of S. pneumonia, S. aureas and S. epidermis. In these controls S. pneumonia shows alpha and beta hemolysis while S. aureas and S. epidermis showed beta and gamma hemolysis respectively. This hypothesis was based on the thought that the upper airway of most people would have at least a small mixture of all three of these bacteria as well as others. This hypothesis was supported by research showing that up to sixty percent of healthy people are carriers of S. aureas (Schmidlin et al.1291), while another study showed that S. epidermis is one of the most commonly found bacterial species on the human body (Otto, 2009, p556). Based on this data, and supported by the control plates, I expected to find all three types of hemolysis on the throat sample collected from a classmate. As expected the throat swab sample did indeed show alpha, beta, and gamma hemolysis which would indicate a mixture of different bacteria in the upper airway.

The second experiment with MSA plates did not turn out as expected. The class control MSA plate for S. pneumonia showed no growth at all and no color change. The lack of growth could be partially explained by the fact that MSA is a selective medium, selecting for staphylococci because of the high salt content, and the lack of color change could be due to the fact that pathogenic species preferentially ferment mannitol and produce acid changing the media color from red to yellow. Another explanation is the possibility of the class control sample showing no growth or color change could be as simple as it being a bad culture. The MSA plates for S. aureas showed both growth and extreme fermentation while the S. epidermis sample...
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