Introduction to Microbiology Lecture Flashcards

Foundations of Cell Theory and Lens Technology

The study of microbiology began to emerge around $1673$ when microscopic lenses were developed to observe small microbes. This led to the development of the cell theory.

• Cell Theory Definition: All living things are comprised of cells. This theory also encompasses the principle that things come from preexisting cells (biogenesis).

• Scientific Debate on Life: There is an ongoing debate regarding viruses (referred to in the transcript as $vios$). While some consider them living, others do not, which challenges the simple definition of cell theory.

• Van Lee and Hook: He was the first scientist to use a simple microscope, which was essentially a simple magnifying glass that allowed him to see smaller microbes. He did not use a complex compound system, but the basic lens was significant.

• Geographic Context of Early Science: Most early microbiology was conducted in Germany and Austria. This region held the superior technology for machining and grinding glass lenses. These advancements led to the creation of the first bifocals, eye care instrumentation, and the microscopes used by students.

The Debate Over Spontaneous Generation vs. Biogenesis

A major historical conflict in science, often involving the church and religious beliefs, was the debate between spontaneous generation and biogenesis. This debate peaked in the mid-$1800s$.

• Spontaneous Generation: The belief that life spontaneously appears from nonliving matter. This was widely accepted historically because it aligned with certain religious and church teachings of the period.

• Biogenesis: The scientific principle that everything must come from preexisting life.

• Francisco Ready ($1668$): Conducted an experiment using jars of meat to disprove spontaneous generation. Jars covered with a barrier (like a mesh) did not develop maggots because flies could not drop their eggs. Open jars developed maggots. This demonstrated that a barrier preventing animal or bacterial entry also prevents life/contamination.

• John Needham: An experimenter who heated nutrient broth and placed it in a sealed, covered flask, but still observed growth. This was used as a "proof" for spontaneous generation, though the growth likely resulted from a contaminated container or contamination during the transfer of the broth.

• Spallanzani: Conducted a similar experiment but boiled the broth while it was already inside the flask to ensure both the solution and the container were sterilized. This resulted in no growth, supporting biogenesis.

• Louis Pasteur ($1861$): Referred to as the "Bill Gates of his time" due to his wealth and aristocratic status. He conducted the conclusive experiment proving biogenesis. He used a long-necked S-shaped flask ($swan-neck flask$) that allowed air in but kept microbes and flies out. The broth inside remained sterile, proving that life does not spontaneously appear even when air (the "vital force") is present. His original flasks are still preserved in his institute today.

Microbial Metabolism and the Chemistry of pH

Microbial metabolism, specifically fermentation, is essential for identifying different types of organisms.

• Fermentation Definition: The process by which microorganisms break down carbohydrates (sugars like glucose, hops, corn, grapes, or wheat). It does not occur with non-carbohydrates.

• Fermentation Products:

  1. Acid

  2. Gas

  3. Alcohol (e.g., ethanol, butanol)

• The pH Scale:

  • Neutral pH is $7$.

  • Acids range from $0$ to $7$. Bases range from $7$ to $14$.

  • The scale is logarithmic (base $10$). A shift of one unit represents a $10$-fold difference. A shift from pH $7$ to pH $4$ is a $1000$-fold difference ($10^3 = 1000$).

  • Human Values: Blood pH is approximately $7.35$ to $7.45$. Human urine is roughly $1000$ times more acidic than blood.

  • Clinical Implications: Small pH shifts in the blood are deadly. Acidosis is a condition where the blood's pH drops. For example, kidney failure prevents the excretion of uric acid and urea, causing acid buildup and confusion.

  • Food and Digestion: Most foods are acidic. Gastric acid in the stomach (pH $\approx 4$) is necessary to uncoil proteins and kill bacteria. Most bacteria prefer a neutral range ($6.8$ to $7$), while fungi prefer acidic environments, which is why fungi grow on fruits.

• BUN and Creatinine: Blood Urea Nitrogen (BUN) and creatinine are measures of kidney function. Nitrogen from proteins is not recycled and must be excreted as urea and uric acid.

Medical Microbiology and Pasteurization

Louis Pasteur's work also extended to food safety and medicine.

• Pasteurization: A process using high heat for short durations to kill pathogens in liquids (milk, orange juice, syrups). It does not kill everything; thermoduric organisms survive.

• Ultra-Pasteurization (UTHT): Higher heat for a shorter time, allowing milk to have a shelf life of a month (e.g., Simply Smart milk). Smaller packets like half-and-half are typically ultra-pasteurized.

• Brucellosis: A disease caused by drinking unpasteurized milk. It results in "undulating fever," a chronic condition that is difficult to eradicate.

• Samuel Weiss ($1840s$): Advocated for handwashing to prevent infections. This was particularly relevant during the Civil War era, where percentage-wise, more people died of microbial infections (gas gangrene, malnourishment) than all other U.S. wars combined.

• Joseph Lister: The first to use chemicals (phenolics/hydrogen peroxide) on surgical wounds to prevent infection.

• Cox Postulates: A series of steps (isolate, grow, transmit, re-isolate) to prove a specific organism causes a specific disease. This is currently applied to research on Epstein-Barr virus (EB) and its link to Multiple Sclerosis (MS).

Immunology and Vaccination

• Edward Jenner ($1798$): Noticed that milkmaids exposed to cowpox were immune to smallpox. He developed the first vaccination using cowpox lesions. The term vaccine comes from $vacca$, meaning cow.

• Smallpox Eradication: Smallpox is the only disease currently eradicated from the human population. The vaccine contained an attenuated (weakened) live virus, which left a characteristic scar. While the last cases were in the $1970s$, some populations received it into the $1980s$.

• Rebecca Lansfield ($1933$): Developed serotypes to identify different groups of bacteria (e.g., Streptococcus groups A, B, C, and D) based on unique antibodies. Group A Strep (Strep pyogenes) causes strep throat and complications like rheumatic fever and kidney failure.

• Fleming: Discovered the first antibiotic, Penicillin, from the fungus Penicillium.

Emerging Infectious Diseases (EID)

• COVID-19: A viral respiratory disease. Early treatments included antibody infusions from survivors.

• West Nile Encephalitis: Virus carried by birds and transmitted by mosquitoes. It causes brain swelling and death and was introduced to the U.S. via ships in $1999$.

• Bovine Spongiform Encephalopathy (BSE): Caused by prions (infectious proteins). Prions are difficult to study because they cannot be grown in a lab and contain no DNA. They are linked to Parkinsonian symptoms.

• E. coli O157:H7: A dangerous strain identified by its cell wall polysaccharide (O157) and flagella protein (H7). It produces an endotoxin that causes severe illness and death. It is the leading cause of diarrhea worldwide. Outbreaks are often traced using these strains to specific farms or irrigation sources.

• Ebola: A hemorrhagic virus with a death rate up to $99\%$. It spreads via bodily fluids. There is currently no effective vaccine for the latest strain because viruses evolve quickly.

• Cryptosporidiosis: A protozoan parasite that causes $30\%$ of all diarrhea. It produces cysts that are resistant to chlorination in water supplies.

• Zika: Transmitted by mosquitoes and sperm. It causes microencephaly (small head size) and birth defects.

• Legionnaires' Disease ($1976$): First identified at an American Legion convention in Philadelphia. The bacteria, Legionella, lived in bird fecal matter on roofs and was misted into the hotel's air conditioning system, causing severe pneumonia in over $480$ people.

Questions & Discussion

• Q: Why do we have to sanitize garden pots?

• A: Pots can harbor microscopic fungi, mold, or bacteria (like powdery mildew) that contaminate new plants. Sanitizing tools and pots prevents the spread of these pathogens.

• Q: How do we sterilize plastic plates?

• A: Plastics cannot be autoclaved (heated). We use gamma irradiation (UV, X-ray, or gamma) to sterilize them, as gases can sometimes leave residues that prevent bacterial growth.

• Q: Are the staining colors in the lab related to urine dipsticks?

• A: No. However, scientific convention often uses pink/red for acidity and blue for bases. This is seen in white blood cell naming: Basophils have blue granules (basic pH), Eosinophils have red/orange granules (acidic pH), and Neutrophils have neutral granules (pH $7$).