Microbiology Exam #4

True or False: while mother’s milk provides components that stimulate the growth of certain microbes, it is sterile.

False

Mutualism

Both organisms benefit

Commensalism

One organism benefits, other is not harmed or benefited

Amensalism

One benefits while the other is harmed

Name the 4 components required for making beer according to the “beer purity law”?

Barley, hops, yeast, water

Which type of alcohol is present in beer? Name one enzyme in humans that metabolizes this alcohol.

• ethanol

• ADH, ALDH, Catalase

Prebiotics

Nutrients that stimulate bacterial species associated with a healthy GI tract

Probiotics

Live cultures associated with a healthy GI tract

What are the 3 most abundant bacterial genera/phylotypes of the human GI tract?

Bacteroidetes, firmicutes, proteobacteria

Why are some microorganisms specialized to only certain parts of the body?

Each environment differs chemically and physically thus providing a selective environment for the growth of certain microorganisms

What is the most abundant bacterial phylotype in saliva?

Streptococcus

What is the most abundant bacterial phylotype in the female progenies tract?

Lactobacillus

Which human microbiota is the most diverse?

Skin

An increase in microbial diversity is associated with health in all human environments except?

Mouth

Contrast microbiome with microbiota

• Microbiome is a functional collection of different microbes in a particular environmental system

• Microbiota describes all the microbes in a microhabitat

What is a holobiont?

Host organism plus its microbiota

Infections with clostridium difficiles often occur after which treatment? What intervention is the best way to treat a C. difficiles infection?

• antibiotic treatment

• Fecal transplant

Name 2 phylotypes that are present at higher levels in obese mice. Name 2 products produced by these phylotypes that are associated with obesity

• firmicutes and methanogens

• Volatile fatty acids and methane

Explain 2 ways the composition of breast milk affects the microbiota of infants.

Breast milk contains oligosaccharides that encourages the growth of beneficial microbes. Additionally, pathogens bind these oligosaccharides rather than to similar carbohydrates on the wall of the infant GI tract. As a result, pathogens are less likely to broke established

What are the 2 ways the human GI microbes influence immune function?

Defense against infection/restrict the growth of pathogens and educates the immune system

How is the acidic pH of the female urogenital tract maintained?

Glycogen is converted to lactic acid

Define infection

Situation in which a microorganism that is not a member of the local microbiota is established and growing in a host, whether or not the host is harmed

Organism W has an LD50 of 3×10^4, organism X has a LD50 of 2×10², organism Y has an LD of 2×10³, and organism Z has an LD of 3×10^4. Which organism is least virulent,

Organism Z

What are endotoxins? Do all bacteria produce endotoxins? Explain.

• Endotoxin is lipopolysaccharide

• No, only gram-negative bacteria produce LPS

What are the 2 ways that a capsule can increase infectivity?

Facilitate attachment to host tissue, protect against phagocytosis from immune cells

What are adhesions?

Receptors made of glycoproteins and lipoproteins on the surface of pathogens important for adherence

What are the 4 steps of the infection process?

Exposure, adherence, invasion, multiplication

In phage therapy, would a temperate or lyric phage be preferable? Why?

Lytic because they will only kill rather than form prophage

Would a phage cocktail or a single phage be preferable in phage therapy? Why?

Cocktail because marks resistance less likely as each phage will ideally each target a unique receptor

What was the source of phase’s used to successfully treat a Mycobacterium abscessus infection using phage therapy?

SEA-PHAGES program

What is an attenuated strain? How are these strains useful to humans?

• Weakened pathogen that can’t cause infection/reduced virulence

• Useful for the development of vaccines

Explain how the production of steptokinase increases Streptococcus pyogenes virulence.

Streptokinase dissolves the clot, releasing the pathogen into the bloodstream and deeper tissues

What type of exotoxins are hemolysins? How do hemolysins kill red blood cells?

• Cytologic exotoxins

• Hemolysins form pores in the cell membrane, causing lysis

Explain in detail the mechanism of action for the diphtheria toxin

AB toxin binds to receptor, AB cleaved, A domain enters cell, toxin adds ADP to EF-2, EF-2 blocks protein synthesis

Which type of toxin is the cholera toxin produced by Vibrio cholera? Explain in detail how this toxin causes massive secretion of fluid into the intestinal lumen, resulting in vomiting and diarrhea

• Enterotoxin or AB toxin

• Toxin activates adenylate cyclase, leading to cAMP production

• This leads to sodium anion movement into the intestinal lumen, which in turn leads to water movement into lumen and symptoms

Explain in detail how the tetanus toxin causes paralysis. Which type of paralysis is caused?

• Toxin blocks glycine release from inhibitory interneuron

• Lack of glycine leads to constant acetylcholine release and constant muscle contraction, triggering spastic paralysis

Explain in detail how the botulinum toxin causes paralysis. Which type of paralysis is caused?

Toxin blocks release of acetylcholine, muscle can’t contract, leading to flaccid paralysis

What is phagocyte? Regarding the phagocytes discussed in lecture, which has neuron-like appendages? Which produces cytokines?

• Cells of the innate immune system that can engulf foreign particles, and can ingest, kill, and digest most bacterial pathogens

• Dendrite

• Macrophages

Describe three properties of innate immunity.

The body’s non-inducible, preexisting ability to recognize and destroy a variety of pathogens or their products, does not require previous exposure to a pathogen, immediate response

What does PAMP stand for? What are PAMPs?

Pathogen-Associated Molecular Patterns are structures and molecules not found in or on hose cells but are common to pathogens (e.g. peptidoglycan, flagellin, dsRNA)

Which enzyme produces HOCl in the phagolysosome?

Myeloperoxidase

Some pathogens have developed mechanisms for responding to the innate phagocytic response. Describe 2 strategies and the organisms that employ them.

• Mycobacterium tuberculosis can survive within the phagolysosome by production of carotenoids to absorb free radicals/oxidative stress

• Streptococcus pyogenes produces leukocidins to kill WBC

• Streptococcus pneumoniae has a capsule that makes it harder to be engulfed by a phagocyte

What are interferons? Which type of cells produce interferons? What is the main function of interferons?

• Cytokines

• Virally infected cells

• IFNs signal to neighboring cells, inducing expression of antiviral cells

What triggers a transmembrane signal transduction that initiates transcription of genes for ingest, kill, and digest most bacterial within phagocytes?

Interaction of a pathogen-associated molecular pattern (PAMP) with a pattern recognition receptor (PRR… or toll-like receptor) on the phagocyte

Describe in detail how natural killer cells target and kill virally infected cells.

Recognize that MHC1 is absent, recognize that the stress protein is present, granules released containing perforin and granzyme, perforin is released to poke holes in the membrane, granzyme trigger apoptosis

List and briefly describe six physical barriers that protect humans from infection.

• Removal of particles by cilia in nasopharynx

• Stomach acidity inhibits microbial growth

• Normal microbiota compete with pathogens in the gut and skin

• Flushing of urinary tract prevents infection

• Blood and lymph proteins inhibit microbial growth

• Rapid pH change inhibits microbial growth

Describe and provide an example of natural passive immunity

Consequence of a person developing their own immune response to a microbe through normal life experiences; infection

Describe and provide and example of natural active immunity.

Consequence of a person developing their own immune response to a microbe through medical procedures; vaccination

Describe and provide an example of artificial passive immunity.

Consequence of a person receiving performed immunity made by another person through medical procedures; immune globulin therapy

Define “tolerance” as it relates to the immune system.

Tolerance is the acquired inability to mount an adaptive immune response against self

What is the function of CD4+ T cells?

CD4 + T cells stimulate B cell differentiation and proliferation

What are the two types of B cells? Which type secrete antibodies?

• Memory and plasma cells

• Plasma cells secrete antibodies

What precisely does an antibody recognize?

Antigen

Immune response triggered by ______ differences cause organ transplantation rejection.

Class I MHC proteins

B cell mature in the ______, and T cells mature in the ______.

Bone marrow and thymus

Why do T cells undergo both a positive and negative selection? Approximately what percentage T cell precursors survive the selection process?

So that mature T cells only react strongly with foreign antigens and not with self

• About 1%

If a virus infects an epithelial cell in the human body, which type of T cells will recognize the infection?

Cytotoxic or CD8+ T cells

Which technique is used to separate proteins by size during a western blot?

SDS-PAGE or gel electrophoresis

Following protein transfer to a membrane in a western blot, a “blocking” step is

performed by incubation with nonfat milk, bovine serum albumin, or other proteins.

Why is this step needed?

To prevent antibody binding non-specifically to the membrane

Ubiquitously expressed proteins are detected and used as a control in a western

blot. What is the purpose of this control?

To ensure equal loading between lanes of the gel/compare to something that

doesn’t vary/ubiquitously expressed; equal transfer

How is the protein of interest visualized/detected in a western blot?

Secondary antibody binds to the primary antibody. The secondary antibody

has been conjugated to an enzyme, such as HRP. The activity of this

conjugated enzyme can then be detected/measured.