Introduction to Infection and Pathophysiology

Introduction to Infection

• Infection is the entry and invasion of foreign materials, such as bacteria and toxins, into the body.
• Symptoms refer to the patient’s subjective complaints, while signs are the objective evidence of infection observed by medical professionals.

Pathophysiology and Pathology

• Pathophysiology involves disturbances in the body’s natural functions due to infection.
• Pathology focuses on anatomical changes that arise from infections.
• Chemopathology deals with chemical alterations occurring during infections.

Non-Specific Immunity (First Line of Defense)

• Non-specific immunity, or innate immunity, provides a general defense against pathogens without specific targeting.
• It comprises physical, chemical, and cellular defenses.

Physical Defenses

• Physical barriers, such as skin and mucosal linings, form the first line of defense against pathogens.
• Mechanical defenses include physical actions like tears and urine flow, which help eliminate pathogens.

Chemical Defenses

• Skin microbiomes inhibit pathogen growth by competing for resources.
• Body fluids contain enzymes (hemokines, lysozymes) and antimicrobial peptides (granulozymes) that combat infections.
• Chemical mediators include antimicrobial peptides, complement components, and cytokines, all of which play vital roles in inhibiting infection.
• Cytokines are essential for cell signaling and immune modulation, produced by macrophages, T lymphocytes, and mast cells.
• Inflammatory mediators include histamine, prostaglandins, leukotrienes, free radicals, and serotonin.

Cellular Defenses

• Granulocytes (e.g., mast cells, basophils, eosinophils, neutrophils) are involved in inflammatory responses.
• Agranulocytes consist of natural killer cells, T cells, and B cells, which are part of adaptive immunity.

Detailed Structures and Functions

• Skin has two layers: epidermis and dermis, and features various cell types; it creates a hostile environment for bacteria.
• Mucosal membranes protect vital systems and produce secretions like mucus and lysozymes to trap and eliminate pathogens.

Specific Chemical Defenses

• Lysozyme, present in tears, saliva, milk, and mucus, hydrolyzes bacterial cell walls, contributing to defense.
• The 16S rRNA gene is crucial for bacterial identification; it has conserved and variable regions useful for taxonomic classification.

Sequencing Techniques

• Traditional methods like Sanger sequencing are time-consuming and less efficient for large-scale sequencing.
• Advanced methods include pyrosequencing and Illumina sequencing, which offer high throughput and detailed analysis.

Modern Sequencing Workflow

• Workflow steps involve DNA isolation, library preparation (PCR amplification, sequencing adapters), sequencing itself, and data analysis.
• Advantages of modern sequencing are high throughput, accuracy, and affordability, whereas limitations include PCR biases and diversity overestimation.

Practical Applications

• Rapid bacterial identification is critical in clinical settings and research focusing on microbial communities.

16S Ribosomal RNA Gene Overview

• 16S rRNA gene is part of the prokaryotic ribosomal RNA, recognized as a "molecular clock" for its conserved structure.
• It consists of 8 highly conserved and 9 variable regions; more conserved regions relate to broader taxonomy (e.g., phylum level).

16S Ribosomal RNA Sequencing

• Used for microbial classification and has a typical sequence divergence of 0.5% to 1% for species identification.
• Advantages include universal distribution across bacteria and minimal horizontal gene transfer issues, while disadvantages involve potential biases and low resolution for closely related species.

Sequencing Workflow

• Begins with DNA isolation, PCR amplification with specific primers, and sequencing through various platforms like Illumina MiSeq, which can analyze multiple species simultaneously.

Sanger vs. Illumina Sequencing

• Sanger sequencing involves chain termination and separates DNA fragments by size via gel electrophoresis, methodically working to determine nucleotide sequences.
• Illumina sequencing employs a high-throughput approach, enabling simultaneous identification of multiple bacterial species from complex samples, without the need for individual culture.

Applications

• The American Gut Project exemplifies the use of next-generation sequencing in analyzing gut microbiomes, showcasing the relevance of modern sequencing technologies in microbiology.

This quiz explores the fundamental concepts of infection, including definitions, symptoms, and signs. It delves into the pathophysiology and pathology related to infections, helping students understand bodily responses to foreign invaders. Test your knowledge on these critical medical concepts.