Step 1b

Question 1

Natural transformers

Answer 1

Definition: uptake of naked DNA from the environment by competent cells (ie cells that are able to bind and import short pieces of DNA) –> DNA released from dead cells is taken up and incorporated by homologous recombination –> result is a modified bacterium

Bacteria capable of this: H. influenza, Streptococcus pneumoniae species, Bacillus species, Neisseria species

Question 2

Parvovirus (B19 pathogenic)

Answer 2

Characteristics: small, ssDNA, naked

Five syndromes:

1. Febrile “slapped cheek” (fifth disease/erythema infectiosum)
2. Transient aplastic crisis
3. arthropathy
4. Pure red blood cell aplasia in immunocompromised
5. Congenital infections –> stillbirth, hydrops fetalis, severe anemia

Question 3

Symptomatic HIV infection and patterns seen

Answer 3

Virus, p24, RNA –> increasing

CD4+ –> decreasing

Anti-p24 (IgG) –> decreasing

Anti-env (IgM) –> staying the same or increasing slightly

Question 4

What is tabes dorsalis?

Answer 4

Degeneration of the dorsal columns and dorsal roots of the spinal cord resulting in:

• loss of pain sensation & peripheral reflexes
• imparement of vibration and position senses
• progressive ataxia

Question 5

Inflammatory diarrhea most common cause

Answer 5

Campylobacter jejuni –> Gm (-), oxidase(+), curved rod

Transmission is fecal oral primarily via contamination of poultry

Question 6

HIV nonprogressors

Answer 6

Infection remains asymptomatic with a stable CD4 count & low or undetectable viremia

Happens if homozygous CCR5 mutation

For infection to take place CCR5 receptors must be expressed (early, macrophages) and CXCR4 (late, T-helpers)

Question 7

Tulamermia

Answer 7

Septicemia and lymphadenopathy common in hunters in Arkansas & Missouri

Caused by Francisella tularensis –> pale staining, slow growing, Gm-, coccobacilli, growth on cysteine

Facultative intracellular organism –> requires cell mediated immunity (th1 and macrophages)

Question 8

Aminoglycoside resistance

Answer 8

• Inactivation of drug by acetylation (enzymatic inactivation)
• efflux