Human Microbiology Exam 1

Quorum sensing

Bacteria release signaling molecules; when concentration reaches a threshold, gene expression changes (e.g., biofilm formation).

Light microscopy (brightfield)

Resolution ~0.2 µm; used for general observation.

Dark-field microscopy

Useful for thin organisms like Treponema pallidum (syphilis)

Electron microscopy

SEM (surface detail), TEM (internal structures).

Resolving power (Resolution)

The ability to distinguish two nearby objects as separate

Unit conversions

1 nm = 10^-9 m; 50 nm = 0.050 µm; smallest unit here = nanometer.

Prokaryotes

No nucleus, single-celled, divide by binary fission.

Flagella

Motility; arrangement affects movement.

Fimbriae

Adhesion to surfaces (important for infection).

Pili

DNA transfer during conjugation.

Glycocalyx

Capsule (organized, virulent) vs slime layer (loose).

Functions of glycocalyx

Prevent desiccation, immune evasion, attachment.

Cell wall

Composed of peptidoglycan (NAG + NAM crosslinks).

Gram-negative bacteria

Outer membrane with LPS (lipid A = endotoxin).

Plasmids

Extra-chromosomal circular DNA; often carry resistance genes.

Psychrophiles

Grow in cold temperatures (refrigeration).

Mesophiles

Moderate temperatures (~37°C); most human pathogens.

Thermophiles

Grows in high temperatures.

Hyperthermophiles

Extreme heat (>70°C). Example: bacteria growing at 75°C = hyperthermophile.

Lag phase

Cells metabolically active, no division yet.

Log phase

Rapid cell division; most growth occurs here.

Stationary phase

Nutrients limited; growth = death.

Death phase

Cells die off.

Gram-positive

Thick peptidoglycan wall → Cell turns purple.

Gram-negative

Thin wall peptidoglycan wall + outer membrane → Cell turns pink/red.

Acid-fast stain

Identifies Mycobacterium (waxy mycolic acid walls)

Penicillins & cephalosporins

Inhibit peptidoglycan synthesis (cell wall).

Quinolones

Inhibit DNA replication.

Aminoglycosides, tetracyclines, chloramphenicol

Inhibit protein synthesis (ribosomes).

Polymyxin B, daptomycin

Disrupt the cell membrane.

Broad spectrum antibiotics

Effective against many bacteria.

Narrow spectrum antibiotics

Targets specific bacteria.

Chemotherapeutic index

Ratio of toxic dose to therapeutic dose; high = safer.

Beta-lactam antibiotics

Contain beta-lactam ring; destroyed by beta-lactamase enzymes.

Sulfonamides

Inhibit folic acid synthesis.

Side effects

Tetracyclines → tooth discoloration; chloramphenicol → gray syndrome.

Pathogenicity

The ability to cause disease.

Virulence

The degree of severity of disease.

Virulence factors

Capsules, enzymes, toxins, biofilms.

Hyaluronidase

Helps bacteria spread through tissues.

Coagulase

Forms clots protecting bacteria.

Exotoxins

Secreted proteins; highly potent.

Endotoxins

Lipid A of LPS in gram-negative bacteria.

Direct contact

Touching, kissing.

Indirect contact

Touching the same objects (Fomites)

Mechanical vectors

Insects carry pathogens externally.

Biological vectors

Pathogen develops inside vector.

Vehicle transmission

Water, food.

Vertical transmission

Mother to fetus.

Incubation

No symptoms.

Prodromal

Mild symptoms (fever, fatigue).

Illness

Severe symptoms.

Decline

Symptoms decrease.

Convalescence

Recovery.

Endemic

Constant presence in region.

Epidemic

Sudden increase in cases.

Pandemic

Worldwide spread.

Carrier

Individual who spreads disease without symptoms.

Normal microbiota

Beneficial bacteria; opportunistic pathogens cause disease when immunity is weakened.