Micro Exam #3 Notes

Actinobacteria:

Characteristics: Gram-positive bacteria

No specific disease caused by all Actinobacteria, but some species can cause diseases like tuberculosis (Mycobacterium tuberculosis) and leprosy (Mycobacterium leprae).

Alphaproteobacteria:

Class from which mitochondria are derived

Bacteroides:

Characteristics: Gram-negative, non-spore-forming, anaerobic bacteria commonly found in the human gut.

Can cause infections such as abscesses and bacteremia.

Cyanobacteria:

Characteristics: Photosynthetic bacteria commonly found in aquatic environments, often capable of nitrogen fixation.

Some species can produce harmful algal blooms (HABs) and release toxins harmful to humans and animals.

Escherichia coli:

Characteristics: Gram-negative, facultative anaerobic rod-shaped bacterium commonly found in the lower intestine of warm-blooded organisms.

Some strains can cause gastrointestinal illnesses, urinary tract infections, and other infections.

Enterobacteriales:

Characteristics: Order of Gram-negative, facultative anaerobic bacteria, including many common pathogens.

Includes genera like Escherichia, Salmonella, and Yersinia, which can cause various diseases including food poisoning and gastroenteritis.

Firmicutes:

Characteristics: Gram-positive bacteria

Includes genera like Staphylococcus, Streptococcus, and Clostridium, which can cause diseases ranging from skin infections to botulism and tetanus.

Halobacteria:

Characteristics: Extremophilic archaea that thrive in high-salt environments such as salt lakes and salt mines.

Generally not pathogenic to humans.

Lactobacillus:

Characteristics: Gram-positive, facultative anaerobic bacteria commonly found in the human gut and other body sites.

Generally considered beneficial, aiding in digestion and maintaining gut health.

Microcystis:

Characteristics: Cyanobacteria genus known for forming harmful algal blooms (HABs) in freshwater bodies.

Can produce toxins harmful to humans and animals.

Prochlorococcus:

Characteristics: Most abundant photosynthetic organism on Earth

Salmonella:

Characteristics: Gram-negative, rod-shaped bacteria commonly associated with foodborne illness.

Various serotypes can cause salmonellosis, gastroenteritis, and typhoid fever.

Spirulina:

Characteristics: Photosynthetic cyanobacteria commonly used as a dietary supplement due to its high protein content.

Streptococcus mutans:

Bacterium causes cavities

Streptococcus pyogenes:

Bacterium causes strep throat infections

Streptococcus thermophilus:

Bacterial species used in making yogurt

Streptomyces:

Characteristics: Gram-positive bacteria known for their filamentous growth and ability to produce antibiotics.

Yersinia pestis:

Characteristics: Gram-negative bacterium, rod-shaped, facultative anaerobe.

Causes bubonic, pneumonic, and septicemic plague, transmitted by fleas.

Staphylococcus:

Characteristics: Gram-positive cocci bacteria, often found in clusters.

Various species can cause skin infections, pneumonia, and other infections.

Clostridium difficile:

The bacterium causes antibiotic-associated diarrhea

Clostridium botulinum:

Bacterium produces botulinum toxin leading to botulism

Clostridium tetani:

The bacterium causes tetanus.

Vibrio cholerae:

Characteristics: Gram-negative, comma-shaped bacterium.

Causes cholera, a severe diarrheal illness transmitted through contaminated water and food.

Borrelia burgdorferi:

Characteristics: Spirochete bacterium.

Causes Lyme disease, transmitted by ticks.

Listeria monocytogenes:

Characteristics: Gram-positive, rod-shaped bacterium.

Causes listeriosis, a foodborne illness often associated with contaminated dairy products and ready-to-eat foods.

Mycobacterium tuberculosis:

Characteristics: Acid-fast, rod-shaped bacterium.

Causes tuberculosis, a potentially serious infectious disease that primarily affects the lungs.

Neisseria:

Characteristics: Gram-negative, diplococci bacteria.

Includes species like Neisseria meningitidis, which causes meningococcal meningitis and Neisseria gonorrhoeae, which causes gonorrhea.

Mycolic acids: Long fatty acids found in the cell walls of Mycobacterium species, such as Mycobacterium tuberculosis. They contribute to the acid-fast property of these bacteria, making them resistant to certain chemical damages and dehydration.

Pyogenic: Refers to bacteria that produce pus. This involves the stimulation of white blood cells and is a common response in bacterial infections such as those caused by Staphylococcus aureus.

Sepsis: A life-threatening condition caused by the body's response to an infection. It leads to tissue damage, organ failure, and potentially death if not treated promptly.

Nosocomial infection: An infection acquired in a hospital or other healthcare facility. Also known as hospital-acquired infections (HAIs), these are often resistant to antibiotics and can be severe.

Vector-borne disease: Diseases transmitted by vectors (organisms such as mosquitoes, ticks, and fleas) that carry infectious pathogens from one host to another.

Zoonotic disease: Diseases that can be transmitted from animals to humans. These infections can be caused by viruses, bacteria, parasites, and fungi.

Reservoir species: Animals or environments that harbor a pathogen and thus serve as a source of infection for other species, including humans.

Virulence factor: Molecules produced by pathogens that contribute to their ability to cause disease. Examples include toxins, surface coatings that inhibit phagocytosis, and enzymes that break down host tissues.

Cytotoxin: A toxin that kills cells. These are often proteins and can cause cell death by disrupting key cellular processes.

Exotoxin: Toxins secreted by bacteria into their surrounding environment during growth. These are highly potent and can cause severe damage to the host.

Endotoxin: A component of the outer membrane of Gram-negative bacteria, specifically lipopolysaccharides (LPS), which are released when the bacteria die. Endotoxins can cause fever and shock in severe cases.

AB toxin: A type of bacterial toxin consisting of two parts: the 'A' component (active) which is typically an enzyme, and the 'B' component (binding) which binds to specific cells allowing the toxin to enter.

Capsid: The protein shell of a virus that encloses its genetic material. It is made up of protein subunits called capsomeres.

Phospholipase: An enzyme that breaks down phospholipids, which are a major component of all cell membranes. This can damage cells and is used by some pathogens to invade or damage host tissues.

Bacteriophage/phage: Viruses that infect bacteria. Phages attach to bacteria and inject their genetic material, often causing the bacteria to lyse (break down) as new phage particles are made.

LD50 (Lethal Dose 50%): A standard measure of the toxicity of a substance, indicating the dose required to kill half the members of a tested population after a specified test duration.

Opportunistic pathogen: An organism that normally does not cause disease in its host but can do so if the host's resistance is low, often seen in immunocompromised individuals.

MIC (Minimum Inhibitory Concentration): The lowest concentration of an antimicrobial that will inhibit the visible growth of a microorganism after overnight incubation.

MBC (Minimum Bactericidal Concentration): The lowest concentration of an antibiotic that will kill 99.9% of the total initial bacterial population during a specified period.

Actinobacteria - Gram positive phylum of bacteria

Alphaproteobacteria - Class from which mitochondria are derived

Cyanobacteria - Only group of bacteria known to carry out oxygenic photosynthesis

Lactobacillus - Important genus of bacteria in dairy fermentation

Neisseria - Species in this genus causes meningitis and gonorrhea

Streptococcus mutans - This species causes cavities

Streptococcus thermophilus - This species is used in dairy fermentation

Streptomyces - Members of this genus are well known for producing antibiotics

2) What is the specific name for a virus that infects a bacterium? Bacteriophage (or phage)

3) Label the basic structures of viruses in the picture below.

A) Capsid

B) Nucleic acid (genome)

C) Envelope (or phospholipid bilayer)

4) Do viruses use RNA, DNA, or both for their genomes?

Both. There are DNA and RNA forms of viruses

5) Are the genomes of viruses single or double stranded or both?

Both, viruses can have single stranded or double stranded genomes.

6) Are the genomes of viruses linear, circular, or both? How does that compare to the chromosomes of bacteria?

Both. In contrast bacterial chromosomes are only circular.

7) Are the genomes of viruses generally smaller or larger than their host?

Smaller

8) Provide a short description of the different stages of viral infection for the cartoon below:

1) Attachment, virion attaches to host cell

2) Penetration or entry of nucleic acid (e.g. DNA) into the host cell

3) Synthesis or replication of the viral genome and proteins

4) Assembly of new viral particles

5) Lysis or release of new virions

9) Imagine that E. coli has a LD50 of 5000 cells per mouse and that V. cholerae has an LD50 of 100 cells per mouse. Which pathogen is more virulent to mice?

V. chlorea. Remember that lower LD50 means more virulent— it requires fewer cells to kill 50% of mice exposed to the pathogen.

10) Are endotoxins typically more or less virulent than exotoxins?

Less virulent. Exotoxins generally are more virulent than endotoxins.

11) Briefly explain how phospholipase functions as a cytotoxin?

Phospholipase is an enzyme that degrades the cytoplasmic membrane of a host cell and thus causes the cell to do through the destruction of its membrane.

12) Briefly explain why flagella, fimbrae, pili, and glyxocalyx all can function as virulence factors in pathogenic bacteria?

All four of these compounds and structures can aid bacteria in adhering or attaching to host cells. Adherence or attachment of bacteria to their target host cell is a critical first step in the infection process.

13) Give a definition of opportunistic pathogen and an example of one given in class:

A pathogen that does not normally infect healthy humans but causes disease in the absence of normal host resistance

Pseudomonas aeruginosa, Staphylococcus aureus, Clostridium difficile

14) List the molecule and the process that each of these classes of antibiotics target. Also give an example of an antibiotic in each class

1) Aminoglycosides Ribosome (translation) | streptomycin, kanamycin, gentaomycin

2) Beta-lactams Cross-linking enzyme (Cell wall synthesis) | penicillin

3) Quinolones DNA gyrase | ciprofloxacin, moxyifloxacin

4) Rifampins RNA polymerase (transcription) | Rifamycin

5) Tetracyclines Ribosome (translation) | tetracycline, doxycycline

15) You grow your bacterial isolate with 10, 20, 50, 100, 200, and 400 µg/ml of the antibiotic gentamycin. Your isolate grows with 10, 20, and 50 µg/ml gentamycin, but not with 100, 200, and 400 µg/ml gentamycin. Based on these results what is the minimum inhibitory concentration (MIC) of gentamycin for your isolate? 100 µg/ml

16) Briefly describe how you would determine the minimum bactericidal concentration for an antibiotic.

Conduct a MIC experiment, as above, growing your bacterium at a variety of concentrations of your antimicrobial. At the end of that experiment, transfer the cultures that show growth inhibition into media without antimicrobials and observe the corresponding minimum concentration at which the bacteria did not grow. That is your minimum bactericidal concentration.

17) What is the difference between a bactericidal and bacteriostatic drug?

Bactericidal drugs kill their target bacteria while bacteriostatic drugs only inhibit the growth of their target bacteria. The effects of a bacteriostatic drug are reversible — you can remove it and the bacteria will grow again.

18) For the concept of selective toxicity, what are the two characteristics that an effective antimicrobial must possess?

The antimicrobial must be effective in killing its target bacteria but at the same time, it must not be toxic or must be limited in the harm it causes the host (humans).

19) Briefly describe two mechanisms by which bacteria can achieve resistance to an antibiotic.

•The bacteria form a biofilm that prevents antibiotics from reaching the cell.

•The bacteria forms a physical barrier around itself that prevents antibiotics from reaching the cell (for example: mycolic acids in Mycobacterium tuberculosis).

•A bacterium gains a mutation that impacts the target protein and thus the ability of the antibiotic to inhibit cells.

•The bacterium obtains a gene for an efflux pump that removes antibiotics from the cell.

•The bacterium obtains a gene for an enzyme that degrades the antibiotic.