Answers to Revise Questions

Describe the relationship between man and microbe in the following:

  • Transients

  • Commensals

  • Opportunists

  • Pathogens

Ans: Transients: microbes briefly in the microbiota. Unable to colonise the body.

Commensals: normal flora of body in symbiosis with the host.

Opportunists: normally harmless in the body but can cause disease when host defences are weakened.

Pathogens: can cause disease; some mildly others strongly virulent.

What are the major groups of organisms and the major differences between them?

Ans: Bacteria: prokaryotes, no nuclear membrane, bacterial RNA, lipid in membranes.

Archaea: prokaryotes, no nuclear membrane, biochemistry different from bacteria.

Eukaryote: organelles enclosed by membrane, including nucleus.

What are the main environments inhabited by the human microbiome?

Ans: Gastrointestinal tract, skin, mouth, upper respiratory tract, vagina.

What are the types of microbes which are found in the different areas inhabited by the human microbiome?

Ans: Bacteria, archaea, viruses, fungi, protozoa/protists, helminths.

List and write brief notes on the major functions of the microbiome in the gastrointestinal tract (GIT).


  • Energy metabolism: important in utilisation of ‘resistant’ starches; high fibre carbohydrates broken down into short chain fatty acids meeting 10% of calorie needs of the body.
  • Vitamin K synthesis: essential for blood clotting. Antibiotics can disrupt function.
  • Drug metabolism: some xenobiotic substances metabolised, may reduce drug efficacy.
  • Development of intestinal structure: stimulate formation of cells in gut epithelium.
  • Maturation of immune system: in constant contact with mucosa and stimulates formation of lymph nodes (Peyer’s patches). Important in maturation of gut and immune system.
  • Prevention of pathogenic infection: they fill ecological niches and prevent transients inhabiting the GIT.

Write brief notes on the implications of antibiotic use for human health.

Ans: Antibiotics can reduce diversity of microbes in the GIT allowing colonisation by ‘foreign’ bacteria and potentially increased incidence of disease. Repeated use of antibiotics is considered to be the main cause of development of antibiotic resistance. Antibiotics kill many of the normal microbiota (as well as the pathogens) leaving behind those that are resistant to the antibiotic which multiply. There is also some transfer of antibiotic resistant genes across species.

What approaches can be used in the management of altered GIT microbiota?


  • Probiotics: for example, live yoghurt. Live microbes promote healthy microbiome.
  • Prebiotics: for example, high fibre not digested until large intestine, stimulates growth/activity of bacteria which promote health.
  • Faecal microbiota transplantation: replaces disordered microbes by normal range and cures recurrent diarrhoea caused by C.difficile.

Outline how the vaginal microbiota varies throughout life.


  • Lactobacilli acquired from mother’s vagina at birth. Later becomes mixed microbes.
  • Reproductive years, different strains of lactobacillus found.
  • Post-menopausal years, as oestrogen levels drop, growth of pathogenic bacteria rises.