Microbial Pathogens through Microbial Growth and Gene Expression

Question 1

A farmer who frequently clears the bush in Dominica with his cutlass presents to the Ross Clinic with a fungal skin infection. Which of the following are most characteristic properties of the agent causing the infection?

A) Double-stranded DNA chromosome in a nucleoid

B) Smooth cytoplasmic endoplasmic reticulum studded with ribosomes

C) Enveloped nucleocapsid encasing a double-stranded DNA chromosome

D) Cell wall containing peptidoglycan and a circular DNA chromosome

E) Ergosterol in the cell membrane of septate hyphae

F) Protein able to induce change in conformation of another protein

Answer 1

E

Question 2

Normal microbiota are first acquired during

A). during birth

B) after one year of age

C). by age five

D). during the first month

E). at age eighteen

Answer 2

A

Question 3

Which of the following concerning Koch’s postulates is incorrect?

A) The infectious agent must be found in the majority of individuals with a particular disease

B) Koch’s postulates cannot be applied to find the agent of all diseases

C) A suspected agent must be able to be demonstrated in the laboratory

D) All of Koch’s postulates must be satisfied before a pathogen can be proven to cause a particular disease

Answer 3

A

Koch’s postulates are as follows:

• The bacteria must be present in every case of the disease.
• The bacteria must be isolated from the host with the disease and grown in pure culture.
• The specific disease must be reproduced when a pure culture of the bacteria is inoculated into a healthy susceptible host.
• The bacteria must be recoverable from the experimentally infected host.

Question 4

All of the following are properties of viruses with of the exception that:

A) they are not cellular

B) they cannot be detected with a light microscope

C) they are composed only of genetic material

D) they are cellular parasites

E) they are smaller than prokaryotes

Answer 4

C

Question 5

Candida albicans is an example of which of the following?

A) nematodes

B) fungi

C) viruses

D) protozoa

E) prokaryotes

Answer 5

B

Question 6

Gastrointestinal tract infections occur primarily through a specific route. Which of the following modes of transmissions and respective countermeasures apply to gastrointestinal tract infections?

A) fecal-orally; proper hand hygiene using soap and water

B) postnatally; omittance of breastfeeding

C) respiratory; covering up when sneezing

D) sexually; proper use of condoms

Answer 6

A

Question 7

A 35-year-old female hiker presents to her physician complaining of diarrhea. She recently had been drinking water from mountain streams, likely contracting an intestinal parasite. Which step of the infectious cycle is associated with excreting contaminated feces containing the parasite through diarrhea?

A) Transmission

B) Adhesion

C) Colonization

D) Invasion

E) Contamination

Answer 7

A

Question 8

A 43-year old diabetic woman complains about genital pruritus and a white-creamy discharge from her vagina indicative of a yeast infection after completing antimicrobial therapy. What agent is most likely responsible for her symptoms?

A) Candida albicans

B) Clostridium perfringens

C) Staphylococcus aureus

D) Pseudomonas aeruginosa

E) Bacillus anthracis

Answer 8

A

Question 9

An experimental protocol requires injecting a new mutant pathogen into mice. The researcher following the protocol notices the next day that all experimentally inoculated animals are dead. Which of the following measurements is associated with the all of the injected mice dying?

A) ID₁₀₀

B) LD₁₀₀

C) ID₅₀

D) LD₅₀

Answer 9

B

Question 10

A researcher is testing the importance of various virulence factors in a bacterial pathogen using site- directed mutagenesis. He converts a codon near the 5’ end of a gene to a stop codon, and notes that the resulting mutants are less able to adhere to mammalian cells in culture. What is the most likely product of the gene he mutated?

A) 16S ribosomal RNA

B) Transpeptidase

C) Flagellin

D) Pilin

E) Type III secretion system component

Answer 10

D

Question 11

A 3-year-old girl presents with a severe cough which produces a loud sound when he gasps for air. Bordetella pertussis is most likely causing the disease. Part of the virulence is autophosphorylation of a sensor and transfer of phosphate to a response regulator. Which of the following best describes this system?

A) Two-component system

B) Biofilm formation

C) Adhesion

D) Formation of the RNA polymerase holoenzyme

E) SOS response

F) Pathogenicity island

Answer 11

A

Question 12

Which of the following nutrients is sequestered by the mammalian system as a protective mechanism and is often the rate-limiting nutrient for bacterial growth?

A. Selenium

B. Glucose

C. Fatty acids

D. Molybdenum

E. Iron

Answer 12

E

Question 13

Sporulation in Bacillus subtilis requires promoter recognition. Which of the following affects promotor recognition of the RNA polymerase?

A) Sigma factor

B) 30S ribosomal subunit

C) 50S ribosomal subunit

D) Sigma replication

E) DNA polymerase I

Answer 13

A

Question 14

In addition to coding for the amino acid methionine, what function does the codon AUG have?

A. termination signal

B. Start signal

C. causes “wobble”

D. marker for introns

E. recognition site for RNA polymerase

Answer 14

B

UGA, UAA, and UAG are stop codons.

AUG is the codon for methionine, and is also the start codon.

Question 15

The binding of sigma factors improves the specificity of a multiprotein complex that carries out which process? A. Conjugation

B. Type III secretion

C. DNA replication

D. Transcription

E. Translation

Answer 15

D

Question 16

Which of the following protein secretion pathways is most commonly used by Gram-positive bacteria?

A. Type II secretion

B. Type I secretion

C. General secretion

D. Type IV secretion

E. Main terminal branch

Answer 16

C

Question 17

All of the following are characteristics of Okazaki fragments EXCEPT:

A) they are checked for accuracy by DNA polymerase III.

B) they make up the lagging strand of replicated DNA.

C) they begin with an RNA primer.

D) they are joined together by DNA ligase.

E) they make up the leading strand of replicated DNA.

Answer 17

E

Question 18

Which of the components of the lac operon is necessary for RNA polymerase binding?

A) Promoter

B) Repressor

C) Permease gene lacZ

D) β-galactosidase gene lacZ

E) Transacetylase gene lacA

Answer 18

A

Question 19

How does short interference RNA (siRNA) work?

A) It binds to and inactivates a target nucleic acid sequence.

B) It binds RNApol and inactivates it.

C) It binds to a regulatory protein, which in turn inactivates a gene.

D) It creates frameshift mutations that produce nonfunctional versions of proteins.

E) It converts heterochromatin to euchromatin.

Answer 19

A

post-transcriptional, noncoding RNAs with important roles in gene regulation

siRNA: It interferes with the expression of specific genes with complementary nucleotide sequences by degrading mRNA after transcription, preventing translation; derived from dsRNA

miRNA: same as siRNA except miRNAs derive from regions of RNA transcripts that fold back on themselves to form short hairpins

Question 20

Transcription terminates after a stem-loop structure is formed in the messenger RNA. Which of the following best describes the process?

A) Sigma factor-dependent termination

B) Rho-independent termination

C) Elongation factor closing

D) DNAse-dependent termination

E) Rho-dependent termination

Answer 20

B

Question 21

A 5-year-old boy has pus-filled vesicles and dry, crusted lesions on his face. A Gram stain of the pustular exudates shows gram-positive cocci in grape-like clusters. What is a unique component of the cell wall of the causative agent?

A. C polysaccharide

B. lipid A

C. lipopolysaccharide

D. lipoteichoic acid

E. M protein

Answer 21

D

Question 22

Which of the following characterizes a Gram-negative bacterium?

A. a thick periplasm, 1 plasma membrane, LPS and teichoic acid

B. a thick periplasm, 2 plasma membranes and LPS

C. a thin periplasm, 2 plasma membranes, no LPS, teichoic acid and lipoteichoic acid

D. the presence of teichoic acid in the cell wall

Answer 22

B

Question 23

If microbial infection is BEST CLASSIFIED by the degree of host damage incurred over time, what are the two primary determinants of infectious disease?

A. antibiotic resistance of the bacterial pathogen and the doubling time of the bacterium

B. status of the host immunity and the virulence properties of the pathogen

C. status of the host immunity and time-to-treatment

D. transitional between commensalism and opportunistic pathogen

Answer 23

B

Question 24

DNA ligase

A) breaks hydrogen bonds between complementary nucleotides.

B) synthesizes short DNA molecules important for the function of DNA polymerase.

C) seals gaps between DNA fragments.

D) proofreads DNA molecules.

E) assists in recognition of promoters during transcription.

Answer 24

C

Question 25

Iron is so important for bacterial growth that bacterial pathogens have highly evolved systems to compete for free iron. What is the key protein to this system?

A. ferredoxin

B. lactoferrin

C. lactoflavin

D. siderophore

E. transferrin

Answer 25

D

Question 26

What is mollicutes?

Answer 26

Question 27

What are SPIROCHETES?

Answer 27

Question 28

What is CHLSMYDIACEAE?

Answer 28

Question 29

Describe Penicillin-binding proteins PBPs

Answer 29

Question 30

Describe PG biosynthesis Phase I

(hint: monomer production)

Answer 30

Question 31

Describe PG biosynthesis Phase II

(hint: if bridge peptide is present)

Answer 31

Question 32

Describe PG biosynthesis Phase III

(hint: translocation and transglycosylation)

Answer 32

note: if you stio bactoprenol or trans….there will be no PG

Question 33

Describe PG biosynthesis Phase IV

(hint: transpeptidation)

Answer 33

Question 34

PG synthesis as a drug target

Describe MOAs of

• beta-lactams
• vancomycin/glycopeptides
• bacitracin

Answer 34

• beta-lactams (penicillin, cephalosporins, etc): inhibit transpeptidases (PBP) –> interrupt construction of PG causing autolysis
• vancomycin: bind the stem peptide D-ala-D-ala –> D-ala cannot be cleaved so no energy to make PG bridge/later processes; no phase III
• bacitracin: prevents recycling of monomer bactoprenol-PP in phase III –> no synthesis of PG & other cell-surface polymers

Question 35

Describe 4 phases of bacterial growth.

(hint: think of graph)

Answer 35

1. Lag Phase: cells are getting ready to grow;
2. Exponential or Log Phase: actual cell growth by 2ⁿ
3. Stationary Phase: growth and metaboolism happening in equal numbers; no increase or decrease in bacteria numbers
4. Death Phase: the number of cells dying > # growing

Question 36

Describe bacterial oxygen growth restrictions.

Answer 36

A. Obligate aerobes (Pseudomonas, Mycobacterium tuberculosis - pneumonia, Bacillus - anthrax)- must have O₂ present for metabolism

B. Microaerophilic (Campylobacter - GI disease, Streptococci)- little O₂ needed

C. Facultative (E. coli - GI, UTI)- can metabolize with or without oxygen

D. Obligate anaerobe (Clostridium - deep wound, food poisoning)- cannot metabolize in the presence of FREE OXYGEN

Question 37

Describe relationship between Iron and bacteria.

Answer 37

Iron acquisition - a critical element of bacterial growth in vivo

Many bacteria secrete small molecules that bind iron (siderophores). Siderophores (with bound iron) are then internalized via receptors by the bacterial cell.

Iron needed for most enzymes and transport. Mammalian host cells have mechanism to hide Iron from bacteria.

Question 38

Selective vs Differential Media

Answer 38

Selective media: One which has a component(s) added to it which will inhibit or prevent the growth of certain types or species of bacteria and/or promote the growth of desired species.

Differential media: One which allows the investigator to distinguish between different types of bacteria based on some observable trait in their pattern of growth on the medium