Micro Exam 4

Plasmid Conjugation

Transfer of an F plasmid from an F+ donor to an F- recipient; results in the recipient becoming F+.

Hfr Conjugation

• Transfer begins at oriT and moves through the chromosome.

• It takes ~100 minutes for the entire E. coli chromosome.

• Most matings are interrupted, so the recipient rarely becomes F+.

• DNA must recombine with the recipient chromosome to be maintained.

What is the "Last Universal Common Ancestor" (LUCA)?

A population of early cells from which cellular life may have diverged into the ancestors of modern-day bacteria and archaea.

Endosymbiont Theory

Mitochondria and chloroplasts arose from a symbiotic association of prokaryotes living within another type of cell.

Nucleus First Hypothesis

Eukaryotes began as a nucleus-bearing lineage that later acquired mitochondria/chloroplasts.

Mitochondria First Hypothesis

An archaeal-like host established an association with an O₂-consuming bacterium (future mitochondrion); the nucleus and chloroplasts came later.

Why is the biological species concept not useful in microbiology?

Because prokaryotes are haploid and do not undergo sexual reproduction.

What are the 16S rRNA gene sequence thresholds for new species and genera?

• New Species: >3% difference from any identified strain.

• New Genus: >5% difference from any identified species.

Selection

Based on fitness; the ability to produce progeny and contribute to the genetic makeup of future generations.

Genetic Drift

A random process that causes gene frequencies to change over time.

Commensalism

Host provides benefit to bacteria, but bacteria provide no benefit or harm to the host (e.g., S. epidermidis).

Mutualism

Both host and bacteria benefit (e.g., E. coli producing Vitamin K).

What is an Opportunistic Pathogen?

Normal flora organisms that cause disease only if the host is compromised (e.g., immune system defect, break in tissue, or loss of other microflora).

Infection

Entry of a pathogen or parasite (does not always cause disease).

Disease

Damage or loss of tissue/organ function due to infection.

Pathogenicity

The measure of an organism's ability to cause disease (often measured by ID50).

Virulence

The measure of the severity of the disease (often measured by LD50).

ID50

Number of organisms required to colonize 50% of hosts.

(Infectious Dose)

LD50

Number of organisms required to kill 50% of hosts. (Lethal Dose)

Exotoxins

Proteins secreted by bacteria that damage the host (e.g., Cholera toxin).

Endotoxins

Bacterial components (like LPS/LTA) released upon cell death/growth; high concentrations can lead to shock and death.

Physical/chemical barriers to infection

• Skin: Keratin, oil, and antimicrobial secretions.

• Stomach: High acidity (low pH).

• Eyes: Lysozyme in tears.

• Respiratory Tract: Muco-ciliary clearance.

Primary roles of the Complement System

• Promote inflammation.

• Opsonize invaders (enhance phagocytosis).

• Lyse the invader (forming pores/MAC).

Cardinal signs of inflammation

• Redness

• Warmth

• Pain

• Edema (swelling)

• Altered function

Innate Immunity

Initial, general response triggered by PAMPs (LPS, Flagellin); includes barriers, fever, and inflammation.

Adaptive Immunity

Secondary, specific response to antigens; retains "memory" for faster future response; involves B and T cells.

Role of CD4

Control/activate immune responses via cytokines or cell-cell interaction.

(Helper)

Role of CD8

Recognize and kill virally infected or tumor cells using perforin and granzymes.

(Cytotoxic)

MHC I

Presents intracellular proteins (viral/cytoplasmic) to CD8 T-cells; found on all nucleated cells.

MHC II

Presents exogenous proteins (acquired via phagocytosis) to CD4 T-cells; found only on Antigen Presenting Cells (APCs).

Endemic

Constantly present at low incidence (consistent cases).

Epidemic

Occurrence in a larger number of people than expected in a specific population/region.

Pandemic

Widespread epidemic, usually worldwide.

Incidence

Number of new cases divided by the population at risk.

Prevalence

Total measure of all disease (new + existing) in a population.

Zoonosis

A disease that primarily infects animals but is occasionally transmitted to humans (e.g., Malaria, Rabies).

BSL-1

Non-pathogenic microbes; general protection.

BSL-2

Pathogens not transmitted by inhalation (e.g., HIV); uses cabinets/gloves.

BSL-3

Serious/lethal infections via aerosol (e.g., TB, Anthrax); requires specialized clothing.

BSL-4

Deadly pathogens with no vaccine/treatment (e.g., Ebola, Smallpox); positive pressure suits required.

Active Immunity

The body produces its own antibodies/memory cells (via infection or vaccination).

Passive Immunity

Ready-made antibodies are introduced (e.g., maternal antibodies or plasma therapy); no memory is formed.