LAB FINAL EXAM BIO 261 Dr. Hassan Q1. Humans are aerobic organisms. If so why do we worry about being infected by an anaerobic organism? Q2. A swab for culture is received from a doctor’s office. The staff forgot to mention the source from where the swab was taken and the clinic was closed for the next few days. What different selective/differential media may be helpful to you to identify the organism. Explain very briefly your rationale for using the particular culture media? Q3. Agar and gelatin are used as a solidifying agent for bacteriological media. Why is gelatin less suitable than the agar? Q4. A catalase test is performed on an isolated colony on a blood agar plate and bubbles appear. The test is repeated on another isolated colony from the same plate. This time there are no bubbles. How can you explain the difference in the results? Q5. You are given a tube of contaminated water. The number of bacteria in the tube is too many to count. You prepare a tenfold dilutions in 5 tubes, so that tube#1 has 1:10 dilution, tube#2 has 1:100 dilution, tube #3 has 1:1000 dilution, tube #4 has 1:10,000 dilution and tube#5 has 1:100,000 dilution. The second tube has 210 cells and the third tube has 26 colonies. What is the number of bacteria per ml in the original sample? Q6. Several individuals have food borne poisoning due to Salmonella from a common source. Later several individuals went to the local emergency rooms of the hospital complaining of similar symptoms. How could you determine and be sure that these individuals have the same infection. Q7. Distinguish between alpha – and beta-hemolysis? Q8. How would you differentiate between Staph. Aureus and Strep.pneumoniae? Q9. Why are females more prone to UTI than males. Q10. What would be the effect of a urine sample being left at room temperature overnight before transported to the laboratory for culture?