Microbiome in Health and Disease

Question 1

Microbiome

Answer 1

-a community of microorganisms inhabiting a particular niche

Dysbiosis: abnormal composition of a microbiome

Question 2

gnotobiotic

Answer 2

-growth in a germ-free environment

Question 3

commensalism

Answer 3

-an interaction between two species in which one benefits, one is unaffected

Question 4

mutualism

Answer 4

an interaction between two species in which both species benefit

Question 5

parasitism

Answer 5

-an interaction between two species in which one benefits, one is harmed

Question 6

immune homeostasis

Answer 6

• balance between a hyper-reactive and unresponsive immune system
• Loss of homeostasis may lead to chronic hyper-responsiveness to microbes and microbial antigens, such as in Crohn’s disease

Question 7

Pathogen exclusion

Answer 7

• commensals compete with pathogens, thus limiting infectivity
• nutrient/receptor competition

Ex: Disruption of gut microbiome by antibiotics increases risk of C. diff infection

Question 8

Structural functions of commensals

Answer 8

• barrier fortification (epithelial tight junctions)

- immune system development (IgA induction)

Question 9

Metabolic function of GI microbiome

Answer 9

• provides 10% of our calories
• synthesize vitamins (B3, B5, B6, B12, K, Biotin, Folate)
• sequester metals
• ferment non-digestible polysaccharides and mucus

-On the other hand: possibility that higher number of Firmicutes (G+) may lead to obesity

Question 10

Name/describe the three “Domains” (three primary lines of descent)

Answer 10

1. Bacteria: unicellular organisms
2. Eucarya: nucleated cells of unicellular and multicellular organisms (includes plants, animals, and microbes)
3. Archaea: unicellular organisms unrelated to bacteria. Includes extremophiles capable of life at high temperature (over 100 deg C) and high salinity

Question 11

List two common pathogens in the phyla: Actinobacteria

Answer 11

• M. tuberculosis

- Corynebacterium diphteriae

Question 12

List two common pathogens in the phyla: Firmicutes

Answer 12

(also known as low G+C gram positives)

• Faecalibacterium prasunitzii (beneficial)
• C. difficile
• Staph aureus
• Strep pneumo
• the human small and large intestine are dominated by obligate anaerobes of the phyla Firmicutes and Bacteroidetes

Question 13

List two common pathogens in the phyla: Proteobacteria

Answer 13

• E. coli
• Shigella
• Salmonella
• Yersinia pestis
• Vibrio cholerae
• H. influenza
• L. pneumophila
• N. gonorrhoeae
• N. menigitidis
• B pertussis
• Rickettsia sp.

Question 14

Development of microbiome in infants

Answer 14

• infants are born sterile
• colonized by trillions of bacteria in days
• in weeks: levels of an adult
• development of immune system occurs in parallel.

Question 15

What environmental factors influence the patterns of colonization in infants?

Answer 15

1. Mode of delivery (Cesarean vs Vaginal)

2. Feeding (breast milk vs. formula)

Question 16

Dysbiosis

Answer 16

• imbalances in microbiome composition
• IBD
• Antibiotic assoc diarrhea (C. diff)
• obesity
• bacterial vaginosis (characterized by a LOSS of protective species)
• “non-bacterial” prostatitis
• pouchitis
• Type 1 diabetes
• Mother to child HIV transmission
• MRSA colonization and infection

Question 17

Crohn’s disease: what is diminished?

Answer 17

Diminished levels of beneficial Clostridium and Bacterioides species

Question 18

What is one of the major challenges in studying the human microbiome and disease?

Answer 18

It is hard to distinguish whether dysbiosis is an etiological factor in a disease or simply and inconsequential secondary effect of disease.