SU_BIO2071_W8_A2_Baker_A

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Jan 9, 2024

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Week 8 Project Ashley R Baker South University Microbiology Lab Professor: Pejmon Afshar Due: December 18 th , 2023 Week 8 Review Sheet Exercise 4 – Streptococci, Pneumococci, and Enterococci Differentiate the microscopic morphology of streptococci and pneumococci as seen by Gram stain. Streptococcus pneumoniae cells are Gram-positive, lancet-shaped cocci (elongated cocci with a slightly pointed outer curvature). Usually, they are seen as pairs of cocci (diplococci), but they may also occur singly and in short chains. When cultured on blood agar, they are alpha hemolytic. Individual cells are between 0.5 and 1.25 micrometers in diameter. They do not form spores, and they are nonmotile. Like other streptococci, they lack catalase and ferment glucose to lactic acid. Unlike other streptococci, they do not display an M protein, they hydrolyze inulin, and their cell wall composition is characteristic both in terms of their peptidoglycan and their teichoic acid (NCBI, 2023). What type of hemolysis is produced by S. pneumoniae? Streptococcus pneumoniae is a fermentative aerotolerant anaerobe. It is usually cultured in media that contain blood. On blood agar, colonies characteristically produce a zone of alpha (green) hemolysis, which differentiates S. pneumoniae from the group A (beta hemolytic) streptococcus, but not from commensal alpha hemolytic (viridians) streptococci which are co-inhabitants of the upper respiratory tract. Special tests such as inulin fermentation, bile solubility, and optochin (an antibiotic) sensitivity must be routinely employed to differentiate the pneumococcus from Streptococcus viridians (NCBI, 2023).

How is S. pneumoniae distinguished from other streptococci with the same hemolytic properties? S. pneumoniae can be differentiated from viridians, some of which are also alpha hemolytic, using an optochin test , as S. pneumoniae is optochin sensitive. S. pneumoniae can also be distinguished based on its sensitivity to lysis by bile . The encapsulated, gram-positive coccoid bacteria have a distinctive morphology on gram stain , the so-called, "lancet shape". It has a polysaccharide capsule that acts as a virulence factor for the organism; more than 90 different serotypes are known, and these types differ in virulence (Bio-libretexts, 2021). Describe the hemolysis produced by alpha-hemolytic, beta-hemolytic, and nonhemolytic streptococci. β-Hemolysis is associated with complete lysis of red cells surrounding the colony, whereas α- hemolysis is a partial or “greening” hemolysis associated with reduction of red cell hemoglobin. Nonhemolytic colonies have been termed γ-hemolytic (Morella, 2018). What type of hemolysis is displayed by the groupable streptococci that are most pathogenic for human beings? Group A beta-hemolytic streptococci (GAS) are known for causing pharyngitis and its sequelae, including acute rheumatic fever and post streptococcal glomerulonephritis. They also cause skin infections and invasive disease. Of all the streptococci, GAS is the most pathogenic for humans (Bio-libretexts, 2021). Reference: Morella, J. (2018). Laboratory manual and workbook in microbiology: Applications to patient care (12th ed.). McGraw-Hill. ISBN: 978-1260093025. Sizar O, Leslie SW, Unakal CG. Gram-Positive Bacteria. [Updated 2023 May 30]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK470553/ Isolation and Identification of Streptococci. (2021, August 1). Community College of Baltimore Country (Cantonsville). https://bio.libretexts.org/@go/page/3453

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