Topic 6 Medical Microbiology

What is the human microbiota?

All the microorganisms present in or on the human body.

What is the human microbiome?

The genomes of all the microorganisms present in or on the human body.

What are commensal microorganisms?

Microbes that coexist with the host without causing harm and may provide benefits.

Digestive Assistance

Gut microbes help digest complex carbohydrates (e.g., fibre) into short-chain

fatty acids (SCFAs) which provide energy and support gut health.

Vitamin Synthesis

Certain gut bacteria produce essential vitamins, such as vitamin K and B vitamins

which the body cannot synthesise on its own.

Enhanced Mineral Absorption

Microbes assist in the absorption of minerals like calcium,

magnesium, and iron by modifying the gut environment.

Training the Immune System

Early exposure to commensal microbes helps the immune system

distinguish between harmful pathogens and harmless microbes,

Regulation of Inflammation

Certain gut bacteria produce molecules that reduce inflammation and

maintain immune balance.

Protection against pathogens

Microbes compete with harmful pathogens by occupying niches,

Skin and Barrier Function

Microbes like Staphylococcus epidermidis help maintain skin barrier integrity

Neurotransmitters Production

Gut microbes produce neurotransmitters like serotonin, dopamine,

and gamma-aminobutyric acid (GABA), which influence mood and mental health.

What is the gut-brain axis?

The communication pathway between the microbiota and the central nervous system.

Toxin Degradation

Certain microbes help degrade harmful substances, such as dietary toxins,

xenobiotics, and carcinogens.

Drug Metabolism

Gut microbes influence the metabolism of medications, impacting their efficacy

and toxicity.

What are Koch's postulates?

1. The suspected pathogen must be found in every case of disease and not be found in healthy individuals.

2. The suspected pathogen can be isolated and grown in pure culture.

3. A healthy test subject infected with the suspected pathogen must develop the same signs and symptoms

of disease as seen in postulate 1.

4. The pathogen must be re-isolated from the new host and must be identical to the pathogen from postulate

What is the first step in the pathogenesis of disease?

1. Exposure to the pathogen.

2. Adhesion of the pathogen.

3. Invasion by the pathogen.

4. Infection.

What is a systemic infection?

An infection that is disseminated throughout the body.

What are endotoxins?

LPS found in Gram-negative bacteria that cause inflammation.

What are exotoxins?

Secreted proteins that damage host cells.

What is an opportunistic infection?

An infection caused by pathogens that take advantage of a weakened immune system.

What is innate immunity?

A rapid, non-specific immune response that does not require previous exposure to a pathogen.

Name three types of phagocytic cells.

Macrophages, dendritic cells, and neutrophils

What are Pathogen-Associated Molecular Patterns (PAMPs)?

Molecules present on the surface of pathogens but not on human cells

Give two examples of PAMPs.

Peptidoglycan and lipopolysaccharide (LPS)

What receptors recognize PAMPs on phagocytes?

Pattern Recognition Receptors (PRRs)

What is one type of PRR?

Toll-Like Receptors (TLRs)

What are the stages of phagocytosis?

1. Engulfment of bacteria

2. Formation of phagosome

3. Binding to lysosome to form phagolysosome

4. Degradation by lysosomal enzymes

5. Release of debris

What are the two key characteristics of adaptive immunity?

Specificity and memory

What does specificity in adaptive immunity refer to?

The ability to target specific pathogens

What is natural active immunity?

Immunity that develops after natural exposure to a pathogen

What is natural passive immunity?

Immunity that involves the transfer of antibodies from mother to child

What is artificial active immunity?

Immunity developed through vaccination

What do antibiotics target?

Bacterial pathogens

What are intrinsic resistance mechanisms?

Natural traits in bacteria that confer resistance to certain antibiotics

What is horizontal gene transfer (HGT)?

The acquisition of resistance genes from other bacteria

What is phage therapy?

Using bacteriophages to specifically infect and kill bacteria

How do phages overcome antibiotic resistance?

By targeting bacterial surface receptors for infection

What is phage-antibiotic synergy (PAS)?

The enhancement of antibiotic efficacy by phages

What are lysins in the context of phage therapy?

Enzymes that break down bacterial cell walls leading to bacterial lysis

Why are lysins particularly effective against Gram-positive bacteria?

Because Gram-positive bacteria lack an outer membrane barrier.

What is challenges of phage therapy?

1. Host specificity, as phages often target specific bacterial strains.

2. Resistance development, where bacteria can develop resistance to phage.

3. Regulatory Hurdles

4. Delivery methods

What are direct detection techniques in medical microbiology?

1. Microscopy: Direct observation of pathogens (e.g., Gram staining for bacteria).

2. Culture Methods: Growth on specific media. Identification by colony

morphology or metabolic traits.

3. Molecular Diagnostics: PCR for pathogen-specific genes (e.g., Mycobacterium tuberculosis detection).

What is an example of an indirect detection method?

Serology, which detects the host's immune response.

What does MALDI-TOF stand for?

Matrix-Assisted Laser Desorption/Ionisation Time-of-Flight Mass Spectrometry.

How does MALDI-TOF identify bacteria?

By analyzing the protein fingerprint, specifically ribosomal proteins.

What is a limitation of MALDI-TOF?

It requires a pure colony on an agar plate first and cannot identify bacteria directly from a patient's blood or urine.

What is the first step in the diagnostic workflow?

Specimen collection, ensuring the sample is not contaminated.

What is the purpose of susceptibility testing?

To determine which antibiotic will be effective against the infection.

What does the term 'empiric treatment' refer to?

Using a broad-spectrum antibiotic before the specific pathogen is identified.

What is a clinical con of molecular (PCR) methods?

It doesn't always prove the bug is alive or causing the current infection.