Bacterial Pathogenesis MCB 103/PMB 103 MIDTERM I Exam | Answered latest spring 2026.

Bacterial Pathogenesis MCB 103/PMB 103 MIDTERM I: Questions 1-7: True/False (14 pts). Please fill-in the box for True or False for each statement below. Make sure you fill in the box entirely and if you change your answer put an X through the box. 1. Which of the following are true of both bacterial and mammalian cells (2 points) T F a. Both move using actin-based motility b. Both have mitochondria c. Both have a cytoplasmic membrane d. Bacteria grow faster than mammalian cells 2. Which of the following are true of peptidoglycan? (2 points) T F a. The vast majority of bacteria have peptidoglycan b. Peptidoglycan provides bacteria with a permeability barrier c. Most mammalian cells lack peptidoglycan d. Target of lysozyme 3. Which of the following are true about beta-lactam antibiotics such as penicillin? (2 points) T F a. Bacteriostatic b. Block protein synthesis c. Acts preferentially on growing bacteria d. Don’t penetrate mammalian cell membranes 4. Which of the following are true about bacterial transposons? (2 points) T F a. Often encode antibiotic resistance b. Generate polar mutations upon insertion into an operon c. Transposition frequency is dependent on the site of insertion d. Transposition frequency is controlled by expression of the transposase 2 5. Which of the following are always true about bacterial plasmids? (2 points) T F a. Restricted to a single bacterial species b. Encode antibiotic resistance c. Specify a pilus d. Cannot exist in a bacterial cell with unrelated plasmids 6. Which of the following is true of type 3 secretion? (2 points) T F a. Auxiliary secretion apparatus of Gram-positive bacteria b. Related to F-pili c. Mediates SecA-dependent secretion d. Allows bacteria to inject proteins into mammalian cells 7. Which of the following influence bacteria gene or protein synthesis (2 points) T F a. Promoter strength b. ribosome binding strength c. mRNA half-life d. DNA G+C content 8. Define each of the following with a short answer. (14 points) Opportunistic pathogen Phage conversion Selective toxicity (of an antibiotic) Polarity RecA Reverse genetics Horizontal gene transfer in bacteria 3 9. The image on the right from lecture 2 shows a Gram stain of two species of bacteria. (4 points) a. Describe the morphology and Gram stain reaction for each (in 3 words each) b. Which one would have LPS? c. Which one would have more peptidoglycan? 10. Matching. Match the term in Column A to the best answer in Column B by writing a letter from column B in the appropriate space in column A. No answer in Column B can be used more than once. (5 points) Column A Column B 11. Two members of the same bacterial species can share less than 50% of their genes. What is this concept called and is how is this possible (4 points) 12. For spontaneous resistance to the following antibiotics, indicate which bacterial gene (or gene product) is the most likely site of mutation that leads to resistance (5 points) Antibiotic Bacterial gene a. Nalidixic acid: b. Streptomycin c. Rifampin b) The spontaneous mutation frequency to rifampin is approximately 10-7 while the mutation frequency to streptomycin is 10-9. Provide a short explanation. 4 c) Why or why not do you think these antibiotic mutations would be clinically relevant.? 13. A bacterial species is grown in rich media under the indicated conditions, and total cell counts are taken at various times. Answer the following questions about its growth: (4 points) Time (min) number of bacteria at 65C number of bacteria at 37C 0 16 16 20 32 24 40 64 32 60 128 48 a. What is the doubling time of this bacterium at 65C? b. What is the doubling time of this bacterium at 37C? c. What words would you use to describe the optimal growth properties of each bacterium? 14. You are testing the efficacy of three antibiotics towards the bacterial pathogen Legionella pneumophila. You start out with 1 X 105 bacteria/ml and add each antibiotic individually to separate cultures containing growth media. Each culture is incubated for 2 doubling times, and then you look to see whether the bacteria are sensitive or resistant to each antibiotic by measuring the viable cell count for each condition after plating on plates without antibiotic: antibiotic 1 antibiotic 2 antibiotic 3 Dilution 1/102 too many too many 11 Dilution 1/103 104 too many 1 Dilution 1/ Dilution 1/105 1 4 0 a. What is the approximate viable cell count after treatment with each antibiotic (in cfu/ml)? (3 points) antibiotic 1: antibiotic 2: antibiotic 3: 5 b. Which antibiotics are Legionella sensitive to, and which are it resistant to? (2 points) c. Which antibiotic, if any, is bacteriostatic? Which antibiotic, if any, is bactericidal? (1 point) d. For antibiotic 3, you measure a total cell count by microscopy after 2 doubling times and find that it is 1 X 103. Is this antibiotic bacteriolytic? (1 points) 6 15. Operons are a fundamental unit of gene organization in bacteria, and a picture of an operon is shown below. Answer the following questions about this operon. a. On the drawing, label the promoter, all ribosome binding sites and terminator. Also draw the RNA that would be transcribed, and indicate how many individual proteins would be translated. (8 points) 16. An E. coli donor contains a plasmid that is temperature-sensitive for replication (it replicates at 30˚C but not at 40˚C). As described in class, the plasmid encodes two antibiotic resistance genes, one for tetracycline resistance that is not transposable and another for ampicillin resistance that is transposable. The recipient is resistant to streptomycin and the donor is resistant to naladixic acid. Conjugation is allowed to proceed for 1h with 109 recipients mixed 1:1 with 109 donors. From the number of CFUs found below, calculate the conjugation frequency and the transposition frequency (6 points) Streptomycin at 40˚C: 109 Streptomycin and ampicillin at 30˚C: 107 Streptomycin and ampicillin at 40˚C: 105 Streptomycin and tetracycline at 40˚C: 2 colonies a. Conjugation Frequency: b Transposition Frequency: c. You are surprised to find two colonies on the streptomycin and tetracycline plates at 40C.You find that the two colonies are nalidixic and ampicillin sensitive. What are these two colonies? 17. In class Dr. Welch and Vance showed a movie of a neutrophil chasing a bacterium. (4 points) a. What is the term (one word) that defines “chasing?” b. What are two molecules that the neutrophil are likely to be detecting? 7 c. Addition of cytochalasin D prevents the neutrophil from chasing the bacterium; what is mechanism of inhibition? 18. G-proteins are molecular switch proteins that are often targeted by bacterial pathogens. Answer the following questions about G-proteins. (10 points) a. Draw a picture of the activation/inactivation cycle of a Rho family G-protein, including the following: active state, inactive state, GTP, GDP, GEF, GAP, exchange and hydrolysis. b. What does GEF stand for? c. What does GAP stand for? d. What would be the effect on G-protein activity of a bacterial toxin that prevents GTP hydrolysis? Choose the single best answer (2 points each) 19. The main reason adaptive immunity is slower to produce protective responses to a new infection than innate immunity is: a. adaptive immune cells must undergo V(D)J recombination of their antigen receptors b. adaptive immune cells specific for a new pathogen are rare and must increase in number c. adaptive immune cells are typically evaded by most pathogens d. adaptive immune cells are highly specific for antigens e. adaptive immune responses exhibit memory 20. Which of these bodily structures does not have any white blood cells? a. brain b. lymph nodes c. liver d. bone marrow e. all of the above have white blood cells 21. Which of the following is an important similarity between the BCR and TCR? a. both can recognize bacterial O-antigen b. both are expressed by phagocytes c. both are generated by V(D)J recombination of gene segments d. both are produced in a secreted form that can bind/neutralize toxins e. none of the above 22. Phagocytosis: a. is an important way that dendritic cells acquire antigen b. is carried out by macrophages better than by T cells c. is important for macrophages to be able to kill bacteria d. can be enhanced by complement e. all of the above 23. Which of the following cytokines is produced by T cells to activate macrophages to kill intracellular bacteria? a. IFN-γ b. TNF c. IL-1 d. type I IFN e. IL-4 24. Which of the following is NOT a characteristic of dendritic cells? a. ability to phagocytose bacterial antigens b. abundant expression of PRRs c. abundant expression of costimulatory ligands Name____________________________________ SID#: 2 d. abundant expression of antigen receptors e. ability to migrate from sites of infection to lymph nodes 25. An antibody binds to a virus and then binds to an Fc receptor on a macrophage to promote macrophage phagocytosis of the virus. This is an example of what process? a. neutralization b. opsonization c. complement activation d. cytotoxicity e. pattern recognition 26. What is a characteristic of MHC class I that is NOT shared by MHC class II? a. presentation of engulfed antigens b. ability to bind to CD4 c. widespread expression on most cell types d. ability to display peptides on the cell surface e. ability to provide costimulation (signal 2) 27. What is a characteristic of CD4 T cells that is NOT shared by CD8 T cells? a. ability to provide signals that activate B cells b. ability to specifically kill infected target cells while sparing neighboring cells c. ability to recognize peptide/MHC complexes d. ability to engulf bacteria and display their antigens on MHC class II e. ability to provide costimulation (signal 2) to APCs 28. Many bacteria produce flagellin protein. By comparing flagellin proteins across bacterial species, it was found that one domain of the protein (called D0) is highly similar across flagellin variants, whereas another domain of the protein (D3) is extremely variable. (a) Name two PRRs that detect flagellin and describe what response is initiated by each of these PRRs after recognizing flagellin [4 points] (b) Predict which domain of flagellin would be recognized by these PRRs, and explain why PRRs would recognize this domain (and not the other domain) [3 points] 3 (c) Is the other domain of flagellin (i.e., the domain not recognized by PRRs) invisible to the immune system? If so, why? If not, what component of the immune system might recognize it? [3 points] 29. Name four distinct kinds of products made by macrophages to kill phagocytosed bacteria and indicate (by circling the answer) which of these would be selectively toxic to a bacterial cell and would not be toxic to a human cell [5 points]. 30. Draw and label a diagram showing how TLRs signal. Label the diagram with the following: TIR, MYD88/TRIF, kinases, TLR, LRR, PAMP, NF-κB, plasma membrane, nucleus. [4 points]