IAS45 Microbes and Disease 2025-26_updated on Oct 22, 2025

1. Antibody response of the host towards microbial components

2. Cellular immune response:

   • Mantoux test (Tuberculosis)

   • Counting number of activated lymphocytes (CD4 or CD8) by specific microbial antigens

Bacteria are classified by colour, cell shape, and arrangement during Gram staining.

Pasteurization requires heating milk to 65 degrees Celsius for 30 minutes to effectively kill bacteria and fungi, except for spores.

The acute symptoms include:

1. Increasing difficulty in breathing
2. Left chest pain on breathing
3. Coughing up yellow sputum with blood streaks

In the usual flask, fermentation is indicated by cloudiness, acidity, and gas production.

Microbiology is defined as the study of organisms which are usually small in size, simple in structure (and neither plants nor animals except in some cases of parasites and algae).

The size range for Viruses is 0.02 μm – 0.1 μm, which is significantly smaller than:

Infection can be simplistically viewed as a form of bacterial fermentation occurring in a living human.

The different types of microbes include:

The tools used to study different types of microbes are:

In a chest X-ray, 'consolidation' refers to the filling of the lung's air spaces with fluid, pus, or other material, indicating a possible infection or other lung pathology.

Penicillin Binding Proteins (PBPs) are essential for the synthesis of the bacterial cell wall. They facilitate the formation of peptide cross-links between glycan chains in peptidoglycan, which is crucial for maintaining cell wall integrity.

Penicillin inhibits bacterial growth by binding to Penicillin Binding Proteins (PBPs), blocking their enzymatic function in building peptide bridges between glycan chains. This disruption leads to cell wall disintegration and osmotic lysis of the bacteria.

The beta-lactam ring is a critical structural component of penicillin that is essential for its antibacterial activity. It allows penicillin to bind to PBPs and inhibit their function, leading to the weakening of the bacterial cell wall.

Antibiotic sensitivity test.

The peptidoglycan layer provides structural strength to the bacterial cell wall and is essential for maintaining cell shape and integrity, making it a target for certain antibiotics.

Both plasmids and the circular chromosomal genome in E. coli C51 can carry antibiotic resistance genes. Plasmids are small, extra chromosomal and self-replicating double-stranded DNA molecules that can contribute to the spread of resistance traits among bacteria.

Bacteria can acquire penicillin resistance through gene transfer from other resistant bacteria, which may involve chromosomal genes or extrachromosomal plasmids that encode resistance mechanisms such as penicillinase production.

Larger zones suggest greater sensitivity, meaning the antibiotic is more effective at inhibiting bacterial growth.

The infectious agent responsible for Tobacco Mosaic Disease is the Tobacco Mosaic Virus (TMV), which is a type of virus that is small enough to pass through bacterial filters.

PCR results are readily visible as a defined size band on gel electrophoresis, while Mycobacterium tuberculosis is not visible on microscopy and requires solid culture medium for colony formation.

Phage transduction is a process where bacteriophages (viruses that infect bacteria) transfer genetic material from one bacterium to another. This occurs when a phage infects a bacterium and, instead of lysing it, integrates its DNA into the bacterial genome. When the bacterium divides, it can pass on the phage DNA, which may include virulence genes, such as the toxin gene from Corynebacterium diphtheriae.

The toxin associated with Tobacco Mosaic Virus cannot be maintained with passaging, leading to dilution and damage over time.

The capsule of Streptococcus pneumoniae is anti-phagocytic, meaning it helps the bacteria evade the immune system by preventing phagocytosis. It is also a target for vaccination to induce protective antibodies, which means that it is used as an antigen. It is encoded by a gene cassette.

Sex pili facilitate the exchange of plasmid DNA between bacteria, allowing for the transfer of antibiotic resistance genes, such as the penicillinase gene.

The laboratory diagnostic tests included:

1. Cell culture to isolate the virus.
2. RT-PCR for detecting viral genes.
3. Serum immunofluorescent antibody test to identify antibodies against the virus.

Flagella provides monbilty, allowing them to escape from white blood cells (WBCs) and navigate their environment.

1. SARS-CoV NP (antigen) is attached to a surface.

2. Serum containing antibodies is added, binding to the antigen.

3. An anti-immunoglobulin enzyme conjugate is added, binding to the antibodies.

4. A substrate is added, which binds to the enzyme and produces a color change if the antibody is present.

5. The microtiter plate shows color change indicating a positive result.

6. Wells with and without color change indicate the presence or absence of antibodies against SARS.

PCR allows for the rapid amplification of specific DNA/RNA segments from slow or difficult-to-grow microbes, enabling detection and diagnosis in a shorter time frame compared to traditional culture methods.

A lower Ct value indicates a higher viral load, meaning there are more copies of the virus present in the sample.

The three main steps in each cycle of PCR are:

1. Denaturation - separating the DNA strands.

2. Annealing - primers bind to the target DNA sequence.

3. Extension - DNA polymerase synthesizes new DNA strands.

Temperature in degree Celsius for each stage: 95, 60-65, 72.

1. Monoclonal antibodies against SARS-CoV NP are attached to a surface.
2. A specimen containing antigens is added, binding to the antibodies.
3. A second antiviral antibody is added, binding to the antigens.
4. An anti-immunoglobulin enzyme conjugate is added, binding to the antiviral antibody.
5. A substrate is added, which binds to the enzyme and produces a color change if the antigen is present.
6. The microtiter plate shows color change indicating a positive result.

Reverse transcription is used to convert RNA into DNA by reverse transcriptase before the PCR process can amplify the target sequence.

The RAP antigen test utilizes an immunochromatographic assay for the capture of antigens and the testing of antibodies.

The purpose is to create a factory (E. coli) that produces the SARS-CoV nucleoprotein (NP), which can then be used as an antigen for animal vaccination to generate specific antibodies.

IPTG acts as an inducer for the lac operon, which triggers the production of the inserted gene product, in this case, the SARS-CoV nucleoprotein, in the E. coli cells.

Sterilization is a physical (or chemical) process that kills or removes all microbes, including bacterial spores, making surgical instruments and medical treatments safe.

1. Find the microbe
2. Develop Diagnostic test
3. Understand how microbe causes damage (pathogenesis & specific countermeasures)
4. What drug for treating patients?
5. How to stop the microbe from spreading from one to another?
6. **How to prevent outbreak from recurrence?

1. Contact: Includes direct contact (person to person) and indirect contact (touching contaminated surfaces).
2. Droplet: Transmission through large droplets (>100um) that travel short distances (fall to ground within 1 meter).
3. Aerosol: Involves smaller particles (<5um to 100um) that can be inhaled and remain suspended in the air for hours.
4. Parenteral: Non-enteral transmission through methods such as arthropod bites, needlestick injuries, surgery, transfusions, or tissue transplants.

• Vaccination
• Antimicrobial treatment
• Monitor for integration of viral genomes into host chromosomes (e.g., HBV and EBV)
• Manage chronic inflammation (e.g., related to Helicobacter pylori and stomach cancer)

The purpose of quarantine is to isolate asymptomatic contacts who have been exposed to infected patients, thereby preventing potential transmission of the virus to others.

• Inhibit microbial replication

• Neutralize toxins released by microbes

• Inhibit toxin release

Decontamination is the general process of reducing microbes to a safe level, typically achieved through hand washing with soap under running tap water.

A lateral flow assay strip typically includes the following components:

1. Absorption pad - where the sample is absorbed.
2. Control line - indicates whether the test is working properly.
3. Test line - shows the presence of the target antigen.
4. Conjugated pad - contains antibodies conjugated to a detectable marker.
5. Sample pad - where the sample is applied.
6. Test tube - for sample collection.

Disinfection is a chemical (or physical) process that inactivates microbes, except for bacterial spores, on body or environmental surfaces. E.g. alcoholic hand rub and bleach denature microbial proteins.

The key components include:

1. Isolation in a single room with:

   • Negative pressure
   • High air change
   • Anteroom

2. Use of personal protective equipment (PPE):

   • N95 mask
   • Face shield
   • Goggles
   • Gown
   • Boots
   • Gloves

The relationship is a balancing act where the virulence mechanisms of microbes (such as their number and toxins) can overcome the defense mechanisms of the host, which upsets human physiology leading to clinically symptomatic disease.

1. Community or hospital setting (outermost layer)
2. Clinical (middle layer)
3. Laboratory (innermost layer)

Outside or inside chromosome.

Only in bacteria cell wall.

Bacilli are characterized as rod-shaped bacteria, which can be straight or curved.

Polysaccharide.

Western blot assay.

• Dampen down excessive inflammatory response

• Target inappropriate innate immune activation (e.g., PAMP receptors)

• Address issues related to molecular mimicry (a foreign antigen shares structural similarities to a host molecule)

Best guess vs gold standard.

Ensure the milk is safe to drink.

Putrefaction refers to the process of bacterial fermentation that occurs in a corpse, leading to the breakdown of tissues and the release of gases and fluids.

The presence of chain spheres in a Gram stain of sputum indicates the presence of Streptococcus pneumoniae, which is a type of Gram-positive cocci that often appears in chains. This suggests a bacterial infection in the respiratory tract.

Gram-negative bacteria appear red after Gram staining.

1. Visualization in clinical specimens:

   • Gram stain and light microscopy for bacteria
   • Electron microscopy for viruses

2. Culture of the microbe:

   • Identification of species

3. Detection of specific microbial components:

   • Proteins (EIA: Ag/Ab)
   • Lipids (chromatography)
   • Polysaccharides (EIA)
   • Specific RNA & DNA sequences (RT-PCR/probe)

Cocci arranged in clusters are referred to as staphylococci.

Spirochaete bacteria are characterized by a spiral shape.

Cocci arranged in chains are referred to as streptococci.

Gram-positive bacteria appear deep purple blue after Gram staining.

Transpeptidase.