Microbiology Lecture 3: Normal Flora and Microbiota

Normal Flora and Microbiota

• Normal flora refers to the permanent microorganisms that inhabit certain body sites, such as the skin, oropharynx, colon, and vagina.
• Human cells to bacterial cell ratio is approximately 1:1.

Microbiome

• The human microbiome consists of microorganisms that live in and on the human body.
• The microbiome is composed of diverse microorganisms, including bacteria, archaea, viruses, fungi, and protists.
• The microbiome plays a crucial role in human health and disease.

Gut Microbiome

• The gut microbiome is composed of two largest phyla: Firmicutes (64%) and Bacteroidetes (23%).
• Firmicutes include gram-positive rods, such as Clostridium and Faecalibacterium.
• Bacteroidetes include gram-negative rods, such as Bacteroides and Prevotella.

Role of Microbiome in Human Health

• The microbiome contributes to human health by:
  • Occupying attachment sites, preventing colonization by pathogens
  • Producing chemical compounds, such as bacteriocins and vitamins B and K
  • Serving a nutritional function, such as producing short-chain fatty acids (SCFAs)
  • Producing metabolites and bioactive compounds

Microbiome in Different Body Sites

• Skin: Staphylococcus epidermidis, Candida albicans, and Staphylococcus aureus are common microorganisms found on the skin.
• Oropharynx: Viridans streptococci, such as Streptococcus sanguinis and Streptococcus mutans, are found in the oropharynx.
• Vagina: Lactobacillus species dominate the vaginal microbiome, maintaining a low pH and preventing the growth of pathogens.
• Urethra: Staphylococcus epidermidis and fecal flora, such as Escherichia coli, are found in the urethra.

Factors Affecting Microbiome

• Diet: Food and drinks can alter the microbiome diversity, such as phosphoric acids in fizzy drinks, coffee, and tea.
• Drugs: Antimicrobials, proton pump inhibitors, and chlorhexidine can disrupt the microbiome.
• Environment: Chlorinated water, processed foods, and fast foods can affect the microbiome.

Microbiome and Disease

• Dysbiosis, or an imbalance of the microbiome, can contribute to various diseases, including enteric infections and oral cavity infections.
• The microbiome can influence the metabolism of drugs, and certain strains, such as Bacteroides dorei, can metabolize multiple drugs.
• The microbiome can also influence the bioavailability of certain nutrients, such as dopamine.