biol-302: 13. microbe host

Define and contrast: symbiosis, mutualism, parasitism, commensalism.

Could a single organism be a commensal sometimes and a parasite at other times? Explain.

symbiosis: living together

mutualism: both partners benefit

parasitism: one partner takes nutrients/resources from the other

commensal: one partner benefits, the other is unaffected

a single organism be a commensal sometimes and a parasite at other times because "the definitions are not absolute, and can shift: " ... today' s benevolent

companion may become tomorrow' s assailant"

Why are mutualisms common in nature?

symbiotic partners have new abilities that they do

not have alone, allowing them to fill new environmental niches

What is an endosymbiosis?

Between which types of organisms are endosymbioses commonly observed?

Give three examples of an endosymbiont

and its host and describe what each partner gains from the endosymbiosis.

a symbiosis in which the bacterial symbiont

lives inside the host's cells

commonly observed in bacteria-invertebrate symbioses, and in some bacteria-plant symbioses

1. the origin of eukaryotic cells

- mitochondria evolved from rickettsiae, a group of bacteria that are obligate intracellular parasites, even now

- chloroplasts evolved from cyanobacteria, a group of photosynthetic bacteria

- many genes were transferred to the nuclear genome or lost, as the endosymbiont came to rely on its host

- Bacteria-like qualities of mitochondria and chloroplasts include: Divide by binary fission; some have FtsZ for septum formation + Protein synthesis like bacteria: initiate with f-methionine, 70S ribosomes + Circular chromosome; no histones

2. Buchnera and insects (aphids)

- Many invertebrates (e.g. insects and worms) have essential bacterial endosymbionts; these are rare in vertebrates

- bacteria-insect mutualisms usually involve nutrition

- example: Buchnera, the bacterial endosymbionts of aphids, can synthesize the 10 amino acids that the aphids cannot make

- bacteriocytes are specialized insect cells in which the cytoplasm is packed with bacterial endosymbionts

3. bacteria and tube worms

- tube worms are gutless animals (up to 2 m long), that survive due to endosymbioses with bacteria (what kind?) that can use inorganic carbon as a carbon source and H2S as an energy source

4. nitrogen-fixing bacteria and legumes

- Biological nitrogen fixation is performed only by prokaryotes

- Nitrogen fixation - conversion (reduction) of N2 to a form utilizable by plants

- symbiotic nitrogen fixation occurs in root nodules formed by the interaction of the bacteria with legume plants

What is the microbiota?

Specifically, where is the microbiota commonly found?

microbiota: usually mutualistic or commensal

Microbiota (bacteria, fungi, viruses, etc.) are commonly found in diverse human body sites

What are some examples of how the human microbiome affects human health?

Describe how the human microbiome can influence drug effectiveness.

How did research by Wallace et al. seek to alleviate side effects of the colon cancer drug CPT-11 (irinotecan)?

human microbiome impacts health by aiding digestion, producing vitamins (K, B), training the immune system, and protecting against pathogens

directly metabolizing drugs (activating prodrugs, inactivating active drugs, or creating toxins), altering drug absorption/bioavailability, and indirectly affecting host immune responses

developing and using potent, selective inhibitors of bacterial beta-glucuronidases (GUSB)

What is an opportunistic pathogen?

Under what conditions would an opportunistic pathogen be able to cause disease?

Define: microbial antagonism.

opportunistic pathogen: organisms that take advantage of particular opportunities to cause disease. These may be organisms that are part of the normal microbiota or not

Failure of the host's normal defenses

- when the host is immunocompromised (i.e. due to HIV, cancer treatment, or immunosuppressant drugs)

Introduction of the organisms into unusual body sites

- example: E. coli in surgical wounds (rather than its usual site, the large intestine)

Disturbances in the normal microbiota

microbial antagonism: normal microbiota ordinarily competes with pathogens for nutrients and space (example: relevance to Clostridium difficile)

Define: virulence factor.

Give examples of the various roles virulence factors may play.

virulence factor: structures or proteins produced by

pathogens that help them to cause disease

aids adhesion, evading host defenses, a toxin

What is/are the virulence factor(s) of C. tetani, the bacteria that causes tetanus?

How do those virulence factor(s) help C. tetani cause disease?

- Clostridium tetani is a Gram positive bacteria that forms endospores; found in soil

- C. tetani is not invasive; enters the host by contaminating wounds

- C. tetani is a strict anaerobe and doesn't survive long in human tissues

Repeat #8 for E. coli O157:H7 and for B. anthracis.

What is/are the virulence factor(s) of E. coli O157:H7?

How do those virulence factor(s) help E. coli O157:H7 cause disease?

virulence factors that allow E. coli O157:H7 to adhere and colonize the surface of the intestinal epithelium

For E. coli O157:H7, infected cattle or people are the usual carriers (a carrier is an infected individual who is a potential source of infection for others.)

What is/are the virulence factor(s) of B. anthracis?

How do those virulence factor(s) help B. anthracis cause disease?

- antiphagocytic capsule (polyglutamyl) which inhibits phagocytosis of the actively growing bacteria

- Anthrax toxin - contains 3 different exotoxins. Together, the exotoxins kill macrophages, which release toxic chemicals, leading to fever, internal bleeding, septic shock, and death

- The genes for these toxins are found on a virulence plasmid.

- In addition (although this would not be considered a "virulence factor"), Bacillus anthracis can form endospores. Anthrax endospores in carcasses of animals previously infected with anthrax can be found in the soil.

Unnecessary antibiotic use can lead to infection by which types of pathogens?

Why?

Unnecessary antibiotic use primarily drives infections by drug-resistant bacteria

antibiotics kill beneficial microbes, create selection pressure for resistant strains, and disrupt immune defenses, allowing these tougher pathogens to thrive, spread, and cause harder-to-treat infections

Would you consider a ribosomal protein (one of the proteins that makes a functional ribosome) to be a virulence factor?

Why or why not?

A ribosomal protein would generally not be considered a virulence factor [1, 2]. The primary reason for this classification is that ribosomal proteins are essential components of the fundamental machinery for protein synthesis in nearly all living organisms, including both pathogens and their hosts