Exam 23: Pathogens and Infection

How does Helicobacter pylori persist in the hostile environment of the stomach?

Modifications of membrane traffic in host cells by three bacterial pathogens are shown in the following schematic drawing. Indicate whether each of the following bacteria is represented by A, B, or C in the drawing. Your answer would be a three-letter string composed of letters A to C only, e.g. BCA. ( ) It is a common cause of food poisoning in humans. ( ) It causes the life-threatening lung infection tuberculosis. ( ) It is the cause of a type of pneumonia known as Legionnaire's disease.

Cytochalasin D (CyD) is a drug that binds to the plus end of actin filaments and prevents actin polymerization. Having identified mutations in actin that confer resistance to CyD, a researcher sets out to study the role of the actin cytoskeleton in the invasion of mammalian host cells by two intracellular parasites: the protozoan Toxoplasma gondii and the bacterium Salmonella enterica. She infects wild-type or CyD-resistant host cells with either wild-type T. gondii, CyD-resistant T. gondii, or wild-type S. enterica, each in the presence (+) or absence (-) of CyD, and measures parasite internalization and intracellular proliferation as a result. The findings are summarized in the table below, in which High or Low levels of proliferation are indicated. According to these results, which column (A to C) do you think corresponds to infection with wild-type T. gondii? Which column corresponds to CyD-resistant T. gondii? Which row (D or E) corresponds to the wild-type host? Your answer would be a three-letter string composed of letters A to E only, e.g. ABE.

Indicate true (T) and false (F) statements below regarding viral cell entry. Your answer would be a four-letter string composed of letters T and F only, e.g. FFTF. ( ) Endocytosis inhibitors can block HIV entry but not influenza virus entry. ( ) Adenovirus infection is blocked by membrane-fusion inhibitors. ( ) Individuals with a defective CCR5 gene are more susceptible to HIV infection. ( ) Most viruses enter the host cell by phagocytosis.

Mycobacterium tuberculosis can cause tuberculosis, a life-threatening lung infection, but can also infect an individual asymptomatically for years. It is not considered to be part of the normal flora, and can infect healthy individuals upon exposure. It can only replicate in the host and thus mainly spreads by direct human contact. Mycobacterium tuberculosis is therefore …

Indicate true (T) and false (F) statements below regarding bacterial, viral, and eukaryotic pathogens. Your answer would be a four-letter string composed of letters T and F only, e.g. TTTT. ( ) Compared to bacteria and viruses, eukaryotic parasites have simpler life cycles. ( ) Most important pathogenic fungi show dimorphism, growing as either yeast or mold. ( ) Protozoan parasites often require more than one host to complete their life cycle. ( ) Plasmodium falciparum can invade human liver and red blood cells, as well as cells lining the gut in female Anopheles mosquitoes.

Toxoplasma gondii is an intracellular eukaryotic parasite that can cause serious human infections. Which of the following is NOT true regarding this parasite?

Indicate whether the epithelium in each of the following organs is (Y) or is not (N) kept almost sterile in a healthy human. Your answer would be a four-letter string composed of letters Y and N only, e.g. YYYY. ( ) Bladder ( ) Cervix ( ) Lower lung ( ) Colon

Sort the following events to reflect the order in which they take place during the infection of intestinal epithelium by enteropathogenicE. coli. Your answer would be a five-letter string composed of letters A to E only, e.g. BCDAE. (A) Actin polymerization and pedestal formation (B) Binding of intimin to Tir (C) Folding of Tir in the plasma membrane (D) Insertion of Tir into the epithelial cell (E) Assembly of type III secretion system

A point mutation in the gene encoding the ? subunit of hemoglobin can lead to sickle-cell anemia. Due to formation of mutant hemoglobin aggregates, red blood cells in affected individuals can adopt a sickle-like shape that interferes with their normal function. Interestingly, individuals carrying this mutation are less vulnerable to malaria infection by Plasmodium falciparum, which replicates inside red blood cells. Accordingly, would you expect the frequency of the mutated hemoglobin allele to be higher in West Africa (A) or in Europe (E)? Write down A or E as your answer.

Both Vibrio cholerae and Bacillus anthracis …

An intracellular pathogen uses one of three major strategies to survive and replicate once inside the host cell, as shown in the schematic drawing below. Indicate which strategy (1, 2, or 3) each of the following pathogens employs for this purpose. Your answer would be a three-digit number composed of digits 1 to 3 only, e.g. 332. ( ) Listeria monocytogenes ( ) Legionella pneumophila ( ) Shigella flexneri

Indicate true (T) and false (F) statements below regarding bacterial and viral evolution. Your answer would be a four-letter string composed of letters T and F only, e.g. FFFT. ( ) Bacteria that reside in natural soil that has not been deliberately exposed to antibiotics are normally sensitive to any antibiotic. ( ) Whereas bacterial and eukaryotic pathogens evade the immune response mainly by genetic recombination, antigenic variation in most viruses occurs by error-prone replication mechanisms. ( ) If an antibiotic targets a vital bacterial protein that cannot be altered in any way to become antibiotic-resistant and functional at the same time, the bacteria would never develop resistance to the antibiotic. ( ) It is impossible to develop effective vaccines against viral infections, since viruses evolve very rapidly.

Indicate true (T) and false (F) statements below regarding the human microbiota. Your answer would be a four-letter string composed of letters T and F only, e.g. TFTT. ( ) The number of human cells in our body is greater than the number of bacterial, fungal, and protozoan cells of our normal flora. ( ) There are far more genes in our microbiome than in our own genome. ( ) Infectious diseases currently cause more human deaths than cardiovascular diseases and cancers combined. ( ) All of the microorganisms that constitute the normal flora are nonpathogens.

In the bacterium Yersinia pestis, which causes bubonic plague, loss of an operon that is normally responsible for iron storage diminishes the ability of the cells to form biofilms and colonize inside the iron-rich gut of infected fleas. Would you expect the efficiency of transmission of plague to increase (I), decrease (D), or remain unchanged (U) as a result of this mutation? Write down I, D, or U as your answer.

Which of the following is a primary pathogen?

You infect human epithelial cells in culture with either nonpathogenic bacteria or Vibrio cholerae, each without any further treatment, in the presence of MDC (an inhibitor of clathrin-dependent endocytosis) or in the presence of filipin (an inhibitor of a clathrin-independent endocytic pathway). You then measure the intracellular concentration of cyclic AMP (in picomoles per milligram of total cell protein) and summarize the results in the following table. Which row (1 or 2) do you think corresponds to infection with V. cholerae? From these results, does cholera toxin enter the cell in clathrin-coated vesicles?

Sort the following events to reflect the order in which they typically occur in viral replication after a virus enters a cell. Your answer would be a four-letter string composed of letters A to D only, e.g. BACD. (A) Replication of the viral genome and transcription of viral genes (B) Virus particle assembly (C) Progeny virion release (D) Virus particle disassembly

Which of the following conditions is NOT expected to provide protection against HIV-1 infection of helper T cells?

The type III secretion system of pathogenic bacteria …