Human Microbiome and Bacterial Pathogenesis

Flashcards reviewing key concepts, definitions, anatomical locations, diseases, and pathogenic mechanisms of the human microbiome based on lecture notes.

What is microbiota defined as in human biology?

The entire collection of microorganisms in a specific niche.

What is the definition of microbiome?

It comprises all of the genetic material within a microbiota.

What are commensals?

Microorganisms that reside on or in the body without causing harm.

What is normal flora?

All of the microorganisms associated with a healthy individual.

What is translocation in the context of microbiology?

Movement of microorganisms from their usual location in the body to sterile body sites.

What are biofilms?

A thick layer of bacteria which has formed aggregates on a surface alongside extracellular material.

In what two physical states do bacteria exist in the human body?

Bacteria exist as planktonic cells and as biofilms.

How do bacteria within a biofilm communicate with each other?

Bacteria within a biofilm communicate via quorum sensing.

What is the importance of the microbe?

Protection from invading microbes by producing antimicrobials

How does the microbiome stimulate the immune system in mucous membranes?

Through the production of surface antibody igA.

How do gut bacteria like E. coli contribute to human nutrition and metabolism?

They can synthesise vitamin K and produce enzymes to break down bile salts and sex hormones for reabsorption.

What defines an opportunistic pathogen in the microbiome?

Microorganisms in the microbiome that do not cause disease normally, but become pathogenic due to changes in the host environment.

What defines translocation in the microbiome?

nfection can occur when bacteria from the microbiome enters regions it is not normally associated with

What four main circumstances affect the human microbiome?

Antibiotics, lifestyle (smoking, foods, supplements), environment (air pollution), and mother-child inheritance (birth and breastfeeding).

What are the five main anatomical locations of microbiotas on and in the human body?

Skin, oral cavity, gut, urogenital tract, and upper respiratory tract.

What microenvironmental factors vary across the skin to create distinct habitats for skin microbiota?

pH, temperature, sebum levels, and moisture.

What is the function of skin microbiota?

acts as a physical barrier to prevent invasion of pathogens, but if it is broken disease can occur

What does oral microbiota use to create a hetereogeneous microbial habitat?

saliva is the source of nutrients and contain antibacterial enzymes to create a favourable environment

How many species of microorganisms are present in the oral microbiota?

750 species.

What bacteria causes endocarditis?

Streptococci

Which bacteria produce lactic acid in dental plaque, causing enamel damage and cavities?

streptococcus sobrinus and streptococcus mutans.

What therapy has a 90% success rate for Clostridium difficle overgrowth and infection?

faecal transplat therapy.

According to this anatomical diagram, which major bacteria are present in the human stomach?

Helicobacter, Proteobacteria, Bacteroidetes, Actinobacteria, and Fusobacteria.

What causes Bacterial vaginosis in the vaginal microbiome?

A reduction in lactobacillus sp. and a subsequent increase in anaerobic microorganisms.

How does thrush occur in the urogenital tract?

When lactobacillus sp. protection is disrupted, c. albicans can overgrow and penetrate deeper vaginal cell layers.

Which bacterial groups can colonise the host mucus layer in the respiratory tract?

gram negative cocci, staphylococci and streptococci sp., and dipheroid bacteria.

How does COPD affect the respiratory microbiome and host lung defense?

It is associated with a change in species dynamic and inflammation, resulting in impairment of the lung innate immune response and an increase in bacteria.

How does asthma affect the respiratory microbiome?

changes between microbiome and development of wheezing

How does cystic fibrosis affect the respiratory microbiome?

mucus build up which can be colonised by resistant bacteria causing chronic and persistent infectionx

What is the difference between pathogenicity and virulence?

Pathogenicity is the ability of a pathogen to infect a host and cause disease, while virulence is the degree of damage or harm a pathogen can cause to a host.

What sequence of steps in bacterial pathogenesis is depicted in this process diagram?

1. Exposure and Adherence; 2. Invasion, Colonisation / growth; 3. Host damage and disease (via Toxicity or Invasiveness).

What is tissue tropism in relation to bacterial adherence?

The selective adherence of microorganisms to specific host epithelial cells through specific molecular interactions between pathogens and host cells.

According to this adherence factor summary table, which protein on Neisseria gonorrhoeae binds to CD66 receptors on epithelium?

Opa protein.

What adherence factors does Streptococcus pyogenes utilize to bind to respiratory mucosal receptors?

M protein and Lipoteichoic acid.

What adherence factors allow Salmonella species and pathogenic E. coli to bind to small intestine epithelium?

Type I fimbriae in Salmonella species, and Fimbral colonisation factor antigens (CFAs) in pathogenic E. coli.

What advantageous roles do biofilms play during Stage 2 (colonisation) of pathogenesis?

They allow cells to remain attached to nutrient-rich surfaces, persist in flowing systems, maintain favourable niches, and evade the host immune system.

In Stage 3 of pathogenesis, how are invasion and toxicity distinguished?

Invasion is the ability to enter host cells and spread to other sites to cause disease; toxicity is the ability to cause disease by a pre-formed toxin that inhibits host cell function or kills host cells.

What are exotoxins?

Highly toxic and specific proteins excreted by gram positive and negative bacteria that travel from the site of infection to cause damage at distant sites.

What are bacterial endotoxins, and with which specific cellular component are they associated?

Heat stable, cell-bound toxins associated with the cell envelope of gram negative bacteria, specifically associated with LPS, especially Lipid A.

How does a cytolytic exotoxin cause cell damage, and what is an example?

It degrades cytoplasmic membrane integrity; an example is alpha-toxin (a-toxin) of c.perfringes.

How does an AB toxin function, and which four bacteria produce AB toxins according to the notes?

The B subunit binds to the host cell receptor and the A subunit causes cell damage. Examples include c. diptheriae (diphtheria toxin), c. Botulinum (botulinum toxin), c. tetani (tetanus toxin), and v. cholerae (cholera toxin).

How does a super-antigen exotoxin operate, and what condition does it cause in staphylococcus aureus?

It stimulates large numbers of immune cells leading to extensive inflammation and tissue damage, causing toxic shock syndrome in staphylococcus aureus.

What severe physiological responses occur when large quantities of bacterial toxin enter the host?

High fever, low blood pressure, increased heart rate, organ failure, disseminated intravascular coagulation, systemic inflammatory response, tissue necrosis, and death.