bacteria

BIOLOGICAL RELATIONSHIPS: HUMANS AND BACTERIA - YOUR MICROBIOME

REVIEW OF CONCEPTS

  • Habitat

  • Niche

  • Ecosystem

  • Species interactions

    • Key principle: Two species cannot coexist stably if they occupy identical niches.

THE HUMAN MICROBIOME

  • Human Composition:

    • Humans are composed of approximately 50% human cells.

    • For every one of your cells, there is one bacterial cell.

    • This relationship indicates that you are more bacterial than human on a cellular level.

  • Microbial Presence:

    • The human gut alone harbors around 100 trillion microbes.

    • There are about 4,000 different species of microbes residing within the intestinal environment.

    • The area of the human colon is comparable to the surface area of a double bed.

MICROBIOME WEIGHT AND POPULATION

  • Microbial Weight: Over a lifetime, a person hosts bacteria weighing the equivalent of five African elephants.

  • Microbial Density: There are more bacterial cells on a human fingertip than the population of Britain.

FUNCTIONS OF THE MICROBIOME

  • The microbiome performs several critical functions, including:

    • Digestion: Aiding in the breakdown and absorption of food.

    • Vitamin Production: Synthesizing essential vitamins.

    • Detoxification: Breaking down harmful toxins.

    • Protection:

    • Crowding out harmful microbes that might cause disease.

    • Killing dangerous microbes through antimicrobial agents.

    • Chemical Production: Producing substances that influence human scent.

    • Body Construction: Guiding structural growth of human bodies.

    • Immune Education: Educating and stimulating the human immune system.

    • Nervous System Development: Affecting the development of the nervous system.

    • Behavioral Effects: Potential influence on human behavior.

MICROBE DIVERSITY IN THE HUMAN BODY

  • The human microbiome consists of diverse microbes, comprising:

    • Prokaryotic Bacteria and Archaea

    • Eukaryotic Fungi and Protists

  • Uniqueness of the Microbiome: Each person’s microbiome is distinct despite having common organisms.

    Examples of Microbial Populations in Different Body Systems:

    • Respiratory System:

    • Streptococcus

    • Haemophilus influenzae

    • Propionibacterium salivarius

    • Neisseria sicca

    • Candida albicans

    • Methanobrevibacter oralis

    • Skin:

    • Staphylococcus acnes

    • Staphylococcus epidermidis

    • Staphylococcus aureus

    • Corynebacterium jeikeium

    • Gastrointestinal Tract:

    • Clostridium perfringens

    • Helicobacter pylori

    • Escherichia coli

    • Bifidobacterium bifidum

    • Urogenital Tract:

    • Enterococcus faecalis

    • Lactobacillus acidophilus

    • Methanobrevibacter smithii

    • Alpha-hemolytic streptococci

INITIAL COLONIZATION AND BENEFITS

  • Initial Colonization: Begins at birth and continues to evolve throughout life.

  • Benefits of Microbial Colonization:

    • Preventing colonization by harmful pathogens.

    • Providing nutritional support and benefits.

    • Stimulating the immune system for better defense against infections.

DIGESTIVE TRACT MICROBIOME

  • Mouth:

    • Habitat: Mutualistic; supports both beneficial and harmful microbes.

    • Mutualistic Examples:

    • Streptococcus oralis: Toxin producers with hydrogen peroxide secretions.

    • Pathogens: Can cause gum disease and tooth decay, forming biofilms.

  • Stomach:

    • Habitat: Primarily houses opportunistic pathogens like Helicobacter pylori, associated with ulcers.

  • Intestines:

    • Mutualistic Microbes: Provide food and vitamins:

    • Escherichia coli - interacts with human cells and produces sugars required by the bacteria.

    • Pathogens: Includes harmful species such as Salmonella and pathogenic strains of E. coli (E. coli O157:H7).

SKIN MICROBIOME

  • Skin Environment:

    • Consists of mutualistic bacteria:

    • Staphylococcus epidermidis and Staphylococcus aureus.

    • Propionibacterium acnes

    • Pathogens: Includes antibiotic-resistant strains like Methicillin-resistant Staphylococcus aureus (MRSA).

ANTIBIOTICS

  • Issues with Antibiotics:

    • Overuse in medical settings and agriculture.

    • Misuse through antibacterial soaps.

  • Function:

    • Antibiotics disrupt certain metabolic functions within bacteria.

    • They are naturally produced by fungi and other bacteria.

  • History:

    • Discovered by Alexander Fleming in 1928; widely used in medical treatments by 1939.

    • Fleming strongly cautioned against misuse in 1945 due to potential issues.

EVOLUTION AND ANTIBIOTIC RESISTANCE

  • Genetic Variation: In any organism population, individuals vary genetically, leading to differing fitness levels.

  • Natural Selection:

    • The environment favors certain genetic variants, promoting their survival and reproduction over generations, resulting in nonrandom changes in allele frequencies.

  • In Absence of Antibiotics:

    • Individual bacteria exhibit similar fitness levels, reproducing uniformly.

  • In Presence of Antibiotics:

    • Resistant bacteria demonstrate higher fitness levels compared to sensitive strains. Sensitive individuals cannot reproduce due to antibiotic effects.

    • Over time, resistant bacteria reproduce more and ensure the propagation of their resistance alleles.

    • Resultant trend: The frequency of resistant alleles rises sharply over generations, exemplifying evolution by natural selection.