2017 Microbiology 1 - Prokaryotic Genetics & Medical Virology

Question 1

What is Reassortment and what types of organisms can participate?

Answer 1

• exchange of genomic nucleic acid segments between strains.
• can take place in some viruses and all eukaryotes
• mechanism by which “genetic shift” takes place

Question 2

What is Transformation?

Answer 2

Uptake of extracellular DNA by bacteria in a particular physiological state (Competency)

Question 3

Gram Positive bacteria that can be transformed by exogenous DNA

Answer 3

Streptococcus pneumoniae
S. aureus
Bacillus subtilis

Question 4

Gram Negative bacteria that can be transformed by exogenous DNA

Answer 4

Neisseria menigitis
Neisseria gonorrhea
Haemophilus influenzae
E. coli

Question 5

Process of transformation of exogenous DNA into bacteria.

Answer 5

1. Transformasome, membrane bound organelles, sequester DNA and transfer it into the cell’s interior
2. Degradation of one DNA strand takes place and the other is used in recombination
3. DNA recombination may depend on specific donor DNA sequences

Question 6

What is Conjugation and how does it work?

Answer 6

Fertility plasmid-facilitated transfer of a plasmid or host chromosome to a recipient cell.
Only occurs between strain of the same or closely related species.

Question 7

Process of Conjugation in Gram-negatives?

Answer 7

1. Extrusion of sex pilus from one bacteria
2. Pilus adheres to outer membrane of Gram-negative cell walls
3. Cells become bound together
4. Plasmid undergoes “transfer replication”
5. One strand of parental DNA is broken and transferred to the second bacteria

Question 8

What is an Episome?

Answer 8

A plasmid capable of replicating into the chromosome.

Question 9

What is the Sex Factors (F factors) and Hfr and their importance?

Answer 9

Sex Factors (Fertility Factors / F) are designated F+ in those that contain it.
Those which lack F factors are F-
When the F-plasmid is integrated into the chromosome it becomes a Hfr (High Frequency Recombination) donor cell.

F+ transfer plasmid only
Hfr transfer plasmid and some chromosomal genes

Question 10

Cell properties that can be carried by plasmids:

Answer 10

Drug resistance
Toxins
Adhesins
Growth Factors
Production of Antimicrobial agents

Question 11

What is transduction?

Answer 11

Can occur in Gram+ or Gram - cells when a fragment of DNA is carried to the recipient cell in a virus (Bacteriophage) produced by donor cell.

Question 12

What are signs of a Viral Infection?

Answer 12

1. dsRNA
2. Expression of viral protein on surface of plasma membrane, causing activation of Tc cells, NK cells and induction of antibody synthesis
3. Formation of inclusion bodies either within cytoplasm or nucleus (very rarely in both)

Question 13

Cytology of Viral Infections: CPE

Answer 13

Viral inducted cytopathologic effects (CPE)

• inclusion bodies
• cell lysis
• vacuolation
• syncytia (multinucleated cells formed by cell fusion)

Question 14

Viral Detection via CPE

Answer 14

• inclusions, plaquesor other cytopathological effects may be characteristic of certain viral infections.
• Heterologous interference - the presence of the infection by one virus can prevent the infection of another.
• Hemagglutination Inhibition - certain infections cause the expression of hemagglutinins (receptors) which cause RBCs to bind (hemagglutination).

Question 15

Viral Detection via Quantization: TCD50, LD50, ID50

Answer 15

Tissue Culture Dose (TCD50) - titer of virus causing CPE in 50% of cultured cells

Lethal Dose (LD50) - titer of virus killing 50% of test animals

Infectious Dose (ID50) - titer of virus infecting 50% of test animals

Plaque forming units - concentration of particules capable of producing a hole in a bacterial lawn or tissue culture monolayer. CPE can also be the end-point in this calculation.

Question 16

Viral Serology

Answer 16

Virus specific IgM indicates recent infection
Virus specific seroconversion - 4x increase in titer between acute and convalescent phase (~3 wk apart)
Antibody timing - first antibodies at 7-10 days are against host-cell or virion surface antigens (envelope/capsid antigens). Later when cells are lysing, internal antigens are released and induce antibody.

Question 17

Type 1 Hypersensitivity

Answer 17

IgE fixed to Mast Cells react w/ virus or viral components, triggering the release of Histamine and SRS-A and ECF-A. These acts to cause anaphylactic type reactions (typically localized)

Question 18

Type 2 Hypersensitivity

Answer 18

IgG/IgM antibodies.
Two types of reactions:
1. Virus (or components) - compliment - antibody complex is fixed to a cell (erythrocyte, leukocyte, platelet), resulting in compliment dependent lysis.Typical of viruses where anemia is one of the clinical manifestations.
2. Viral component (commonly capsid protein) may be expressed on cell. Antibody and compliment bind to infected cell and cause lysis of cell. Thought to be major mechanism of viral-induced cell lysis in tissues.

Question 19

Type 3 Hypersensitivity

Answer 19

IgG and/or IGM antibodies form complexes w. viral antigens and complement, generally neutrophil chemotactic factors, with resultant local tissue inflammation and destruction.

Question 20

Type 4 Hypersensitivity

Answer 20

Does not involve antibody.
Sensitized T-lymphocytes react directly with viral antigen, usually that antigen expressed on the surface of infected cell.
Inflammation produced through action of lymphokines and lysing the infected cell.
Second most common hypersensitivity reaction to viruses.