Mycobacterium Tuberculosis & Disease

• Tuberculosis is caused by Mycobacterium tuberculosis

Mycobacterium tuberculosis Characteristics

• Obligate aerobe
• Grows as thin rods that can grow individually or clump together

Tuberculosis Symptoms

• Many people infected clear the infection immediately.
• Stage 2 involves the bacteria getting walled off in the lung and continuing to divide and proliferate.
• This wall calcifies at the end of the initial infection and can be seen on an X-ray.
• The disease enters a latent stage without symptoms.
• During the final stage, miliary disease, the patient's immune system fails.
• Canonical symptoms include pale skin, coughing, weakness, and blood-tinged sputum

Mycobacterium tuberculosis: Acid-Fastness

• An outer coating of mycolic acid causes Mycobacterium tuberculosis to be acid-fast.
• The immune system releases inflammatory mediators due to mycolic acid.

Tuberculosis Transmission

• Transmitted via inhalation of the bacterium from someone who has it coughing.

What Happens to M. tuberculosis Cells in the Lungs

• Macrophages usually phagocytose and digest M. tuberculosis once inside the lungs.
• However, the bacteria survive and proliferate.

PPD Skin Test

• Proteins from M. tuberculosis are injected under the skin
• After 2-3 days, look for induration or swelling
• Induration indicates previous exposure to TB or another mycobacterium.

Mycobacterium tuberculosis and Immune System Failure

• In the miliary phase, the bacteria escape the lungs.
• The infection then spreads to other parts of the body.
• The name comes from millet grains because it resembles them.

Positive PPD Skin Test

• Confirm the infection with X-rays.

Tuberculosis Treatments

• First-line treatment is a cocktail of four drugs, including isoniazid, ethambutol, and rifampin.
• Treatment lasts for about 6 months to prevent M. tuberculosis from becoming antibiotic-resistant.

Tuberculosis Relevance Today

• Remains important due to the high number of HIV-positive individuals
• Immunocompromised individuals can become infected with tuberculosis more easily.

Growth Factors: Physical vs. Chemical

• pH, Osmotic Pressure, and Temperature are physical.
• Carbon, Phosphate, Organic Growth Factors, Sulfur, Nitrogen, and Trace Elements are chemical.

Organism Types and Temperature

pH Ranges for Growth

• Most bacteria grow well between pH 6.5-7.5.
• Molds grow best between pH 5-6.
• Acidophiles grow in acidic conditions.
• Alkaliphiles grow best at pHs past 9.5

Osmotic Pressure

• Osmotic pressure is the force that drives water into or out of a cell to balance the amount of solutes on both sides of the membrane
• Placing an un-walled bacterium in a hypertonic environment results in water leaving the cell, leading to shriveling.
• Facultative halophiles can tolerate these environments.
• Extreme or obligate halophiles are adapted to high-salt environments and must live there.

Cell Use of Chemicals

• Carbon is used in organic molecules like DNA, RNA, Proteins, Lipids, Carbohydrates.
• Nitrogen is used in DNA, RNA, proteins, ATP.
• Sulfur is used in certain amino acids, thiamine, and biotin.
• Phosphorous is used in DNA, RNA, Protein, ATP, and Phospholipids.
• Trace Elements serve as enzyme cofactors.
• Oxygen can be used as a terminal electron acceptor by some cells, while others cannot. It's also part of many biomolecules.
• Organic Growth Factors are other things cells need like vitamins, amino acids, purines, and pyrimidines. These are used in a lot of biomolecules.

Organism Growth in Stab Culture

• Obligate aerobes: At the top of the culture tube.
• Obligate anaerobes: At the bottom of the tube, where there is no O2
• Facultative anaerobes: Concentrated at the top of the tube but distributed throughout
• Aerotolerant Anaerobes: These will be spread evenly throughout the tube
• Microaerophiles: concentrated somewhere in the tube where the O2 level is optimal (not the top or the bottom)
• These locations have the right amount of oxygen; for example, obligate anaerobes die in the presence of O2

Oxygen Toxicity

• Certain forms of oxygen are toxic.
• Aerobes and facultative anaerobes detoxify these toxic oxygen species, like singlet oxygen, superoxide radicals, peroxide anions, and hydroxyl radicals.
• Superoxide dismutase is an enzyme that neutralizes toxic forms of oxygen.

Organism Growth Factors

• Organic growth factors are vitamins, amino acids, purines, and pyrimidines.
• Cells need to obtain these from their environment.

E. coli Location in the Human Body

• Found in the intestinal tract

When E. coli Becomes Dangerous

• It starts making toxins or is found where it doesn't belong.

E. coli Pathogenicity

• They acquire genetic elements that allow them to invade the epithelium layer lining the intestines.

E. coli Types and Pathogenicity

Shiga-like Toxin

• Similar to Shigella toxin
• Kills the intestinal epithelia and prevents the absorption of water and other materials.

Shiga Toxin

• Produced by Shigella spp.
• Acts the same way as shiga-like toxin

Treating E. coli with Penicillin

• Not recommended because it would cause the release of more enterotoxin/LPS from the bacterium.
• The release could lead to symptoms associated with endotoxins and can lead to shock.

E. coli Source and Food Contamination

• The intestines of cattle
• Enters the food supply when food is improperly cooked or veggies are contaminated through runoff.

Foodborne E. coli

• Not all cases are foodborne
• Children can contract the disease from petting zoos or fairs if they don't wash their hands.

Hemolytic Uremia Syndrome

• A complication of E. coli infection, involving blood in the urine, is called hemolytic uremia syndrome.
• It can lead to kidney failure and occurs in 5-10% of children who get E. coli infection.

Enterotoxic E. coli

• E. coli that is secreting endotoxins.
• It's fatal in children under 5 and has cholera-like symptoms.

Traveler's Diarrhea

• Diarrhea associated with traveling to a new place.
• Caused by different microbes in the water than what one is familiar with.
• Possible causes include E. coli, Shigella spp., Campylobacter, viruses, or protozoa.
• If it gets bad, oral rehydration salts, Lomotil, or antibiotics can treat it.

Culture Media

• Provides microbes with the nutrients they need to grow in the lab instead of within their normal environment.

Chemically-Defined Medium

• Media with an exact, known chemical concentration.
• Chemotrophs grow best in this medium.

Complex Medium

• A medium with an exact, known chemical concentration, chemoheterotrophs grow best here.
• Heterotrophic bacteria and fungi grow best in complex media
• Complex media are made from nutrients found in extracts from plants, fungi, and other sources.
• The exact amount of chemicals are unknown

Solid Media Creation with Agar

• Agar, a polymeric substance made by algae is used to create solid media
• Bacteria and yeast cannot metabolize agar and it remains solid.

Oxygen and Anaerobes

• Oxygen is everywhere, which means it is hard to grow obligate anaerobes, as oxygen is frequently toxic to them.
• Reducing media contains sodium thioglycolate that depletes oxygen in the medium.
• Cultures can also be put in tightly sealed places with pouches of citric acid that reacts with and consumes all the oxygen.

Working with Anaerobes

• Boxes and chambers that are sealed with all of the oxygen replaced with inert gases like nitrogen.

Armadillos in Science

• Armadillos are used to grow certain bacteria like Mycobacterium leprae
• This is because their body temperature is the optimal growth temperature for these microbes.

Capnophiles

• Organisms that grow in anaerobic environments with a high level of carbon dioxide.
• They are grown in candle jars where candles consume all of the oxygen and replace it with carbon dioxide
• Packets of chemicals that generate CO2 can also be used.

Biosafety Levels

• Level 1: Minimum safety requirements, generally non-hazardous; Agrobacterium spp, E. coli
• Level 2: Gloves, goggles, a lab coat; Staph aureus, HIV
• Level 3: All previous precautions and biosafety cabinets; Yellow fever, West Nile Virus, TB
• Level 4: All previous precautions, respirator, negative pressure, isolation gear; Ebola and Marburg

Selective Media

• Media that gives an advantage to a specific population of organisms
• Antibiotics can select for a population of cells that has resistance to it and kills all microbes that don't.

Differential Media

• Contains a factor like blood that certain cell populations can metabolize and others cannot.
• Used to differentiate different species or strains apart.

Enrichment Culture

• A specially designed culture can be used to select for and enrich or grow more of a specific organism that is at a low abundance in a sample.

Ulcers

• Caused by Helicobacter pylori.

Helicobacter pylori Infection

• Not everyone infected gets gastritis, ulcers, and stomach cancer

Helicobacter pylori Adaptation

• Burrows into the mucosa and makes urease.
• Urease converts urea into ammonia, which neutralizes stomach acid.

H. pylori Symptoms

• Acute infection: gastritis, abdominal pain, and vomiting.
• Chronic condition: progresses to abdominal tenderness, even when the stomach is empty, lack of appetite or bleeding, and stomach cancer.

H. pylori Immune System Evasion

• Have modifications to their LPS

H. pylori Prevention

• There is no vaccine

Ulcer Treatment

• Treated with a cocktail of drugs, including proton-pump inhibitors and OTC medications like Pepto-Bismol®.
• If treatment fails, salvage therapy is tried.