Micro Exam #3 Notes

Actinobacteria

Gram-positive phylum of bacteria

Alphaproteobacteria

Class from which mitochondria are derived

Bacteroides

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

Can cause infections such as abscesses and bacteremia.

Cyanobacteria

Only group of bacteria known to carry out oxygenic photosynthesis

Some species can produce harmful algal blooms

Escherichia coli

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

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

Includes genera like Escherichia, Salmonella, and Yersinia

Firmicutes

Gram-positive bacteria

Includes genera like Staphylococcus, Streptococcus, and Clostridium

Halobacteria

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

Lactobacillus

Important genus of bacteria in dairy fermentation

Microcystis

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

Prochlorococcus

Most abundant photosynthetic organism on Earth

Salmonella

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

Spirulina

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

Neisseria

Species in this genus causes meningitis and gonorrhea

Streptococcus mutans

This species causes cavities

Streptococcus pyogenes

Bacterium causes strep throat infections

Streptococcus thermophilus

This species is used in dairy fermentation

Streptomyces

Members of this genus are well known for producing antibiotics

Yersinia pestis

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

Staphylococcus

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

Causes cholera

Borrelia burgdorferi

Causes Lyme disease, transmitted by ticks.

Listeria monocytogenes

Causes listeriosis

Mycobacterium tuberculosis

Causes tuberculosis

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, often proteins that disrupt key cellular processes

Exotoxin

Toxin proteins excreted from the pathogen

Endotoxin

Toxic lipopolysaccharides on outer membrane

Only Gram -

Not soluble, requires direct contact.

Induces response from body: fever

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.

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.

Lower LD50 = More virulent

Opportunistic pathogen

An organism that normally does not cause disease in its host but can do so if the host's resistance is low

Pseudomonas aeruginosa, Staphylococcus aureus, Clostridium difficile

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.

Bacteriophage (or phage)

Specific name for a virus that infects a bacterium

A

Capsid

B

Nucleic acid

C

Envelope

Both

Viruses use RNA, DNA, or both for their genomes

Both

Genomes of viruses are single or double stranded or both?

Both

Genomes of viruses are linear, circular, or both?

Smaller

Are genomes of viruses generally bigger or smaller than their host?

Attachment, Penetration, Synthesis, Assembly, Lysis

Different stages of viral infection

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

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?

Less virulent. Exotoxins generally are more virulent than endotoxins.

Are endotoxins typically more or less virulent than exotoxins?

Phospholipase

Functions as a cytotoxin by degrading the host cell membrane

Adherence/Attaching

Flagella, fimbrae, pili, and glyxocalyx can function as virulence factors

Opportunistic pathogen

Pathogen that causes disease in immunocompromised individuals

Aminoglycosides

Ribosome (translation) | streptomycin, kanamycin, gentamycin

Beta-lactams

Cross-linking enzyme (Cell wall synthesis) | penicillin

Quinolones

DNA gyrase | ciprofloxacin, moxyifloxacin

Rifampins

RNA polymerase (transcription) | Rifamycin

Tetracylines

Ribosome (translation) | tetracycline, doxycycline

100 µg/ml

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?

Bactericidal drugs

Kill its target bacteria

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.

Selective toxicity

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).

Antibiotic Resistance

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

Antibiotic Resistance

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

Antibiotic Resistance

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

Antibiotic Resistance

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

Antibiotic Resistance

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