Please answer the question in the picture. QUESTIONS 1. Is blood agar selective
ID: 3166252 • Letter: P
Question
Please answer the question in the picture.
QUESTIONS 1. Is blood agar selective or differential? Briefly explain. 2. Is the Gram stain of significant importance in identifying the organisms studied in this exercise? Explain. 3. You have isolated gram-positive cocci from a throat culture that you cannot identify as staphylococci or streptococci. A test for one enzyme can be used to distinguish these bacteria quickly. What is the enzyme? CRITICAL THINKING 1. A 45-year-old man was admitted to the hospital with chest and back pain. On examination, his chest was dull to percussion. A chest X-ray film shows lower left lung infiltrates. A sputum culture reveals alpha- hemolytic, gram-positive, catalase-negative cocci that were inhibited by optochin. The bacteria produce acid from lactose. Identify the species of this bacterium. Assume that you isolated non-acid-fast, gram-positive, catalase-positive rods from your throat. Does this represent a disease state? Briefly explain.Explanation / Answer
1) Blood agar is considered differential because it is used to distinguish pathogenic bacteria based on the effect of bacterial enzymes known as hemolysins which lyse red blood cells. Blood agar is mainly used clinically to detect the presence of Streptococcus pyogenes, the human pathogen which causes "strep throat".
2) Staphylococcus as well as Streptococcus are gram-positive organisms, so gram staining has little importance in identification of microbes here in this case.
3) Catalase is the enzyme used for differentiating between staphylococci and streptococci. The main criterion for differentiation between Staphylococcus and Streptococcus genera is the catalase test. Staphylococci are catalase positive whereas Streptococci are Catalase negative. Catalase is an enzyme used by bacteria to induce the reaction of reduction of hydrogen peroxide into water and oxygen.