Microbiology and Disease: Tuberculosis, Microbes, and Human Health

Tuberculosis (TB)

Disease caused by Mycobacterium tuberculosis.

Signs & Symptoms of TB

Persistent cough, fatigue, weight loss, coughing blood.

X-ray findings in TB

Infiltrates (white wisps) and cavitation (holes in lung tissue).

Diagnosis of TB

PCR (polymerase chain reaction) and DNA sequencing of sputum/biopsy.

Treatment of TB

Antibiotics (isoniazid, rifampin); MDR-TB requires surgery + multi-drug therapy.

Species vs. Strain

Scientific names italicized (Genus capitalized, species epithet lowercase).

Species definition

≥97% DNA similarity = same species; small differences = different strain.

Strains

Strains can alter pathogenicity and drug resistance.

Microbe definition

Organism too small to see without a microscope.

Cell

Smallest unit of life.

Microbial size

Ranges from millimeters to 0.2 micrometers.

Viruses

Non-living (no metabolism, no independent reproduction); require host cell.

Genetic material in viruses

May be DNA or RNA.

RNA viruses

Mutate faster (e.g., flu, SARS-CoV-2).

Nitrogen fixation

Only bacteria & archaea convert atmospheric N₂ → amino acids.

Vitamin production by microbes

Gut microbes release vitamins during digestion.

Cellulose digestion

Bacteria produce cellulase → breakdown plant cell walls → byproducts = gas.

Primary producers

Convert CO₂ → sugars; critical in ecosystems (especially where plants cannot live).

Pathogens

Very small fraction (<1%); most microbes are harmless or beneficial.

Three Domains of Life

Bacteria (prokaryotes, some pathogens), Archaea (prokaryotes, no known pathogens), Eukarya (eukaryotes; include fungi, protozoa, algae, some parasitic worms).

Prokaryotes

No nucleus (Bacteria, Archaea).

Eukaryotes

Have nucleus and organelles.

Black Death (Bubonic Plague)

Caused by Yersinia pestis; reservoir: rats → vector: fleas.

Symptoms of Black Death

Enlarged lymph nodes = buboes.

Historical explanations for Black Death

Miasma ("bad air"), divine punishment, scapegoating of Jews.

Discovery of Microbes

Robert Hooke: built first compound microscope, coined 'cell' (1665).

Anton van Leeuwenhoek

First to observe bacteria ('animalcules') with single-lens microscope.

Louis Pasteur

Disproved spontaneous generation; showed microbes are in the air → Germ Theory of Disease.

Florence Nightingale

Founder of modern nursing, used medical statistics to link infections with soldier mortality.

Robert Koch

Developed Koch's Postulates to connect microbes to disease.

Immunization

Variolation (smallpox scabs → nasal inoculation, risky).

Edward Jenner

Cowpox vaccination protected against smallpox (first true vaccine).

Louis Pasteur (vaccines)

Attenuated strains used in vaccines (e.g., rabies, cholera).

Antiseptics & Disinfectants

Ignaz Semmelweis (handwashing), Joseph Lister (surgical antiseptics).

Antiseptics

Used on tissue; disinfectants = used on objects.