Microbiology, Virology & Immunology

MB, VIR, & IMM are interconnected fields critical to understanding life, disease, and host defense. MB studies microorganisms (bacteria, archaea, fungi, protozoa), VIR focuses on viruses, viroids, & prions, while IMM investigates the host's defense mechanisms against pathogens and other foreign substances. Together, they form the bedrock of infectious disease understanding, public health, and therapeutic development.

## Microbiology Fundamentals

MB encompasses PRK (bacteria, archaea) and EUK (fungi, protozoa, helminths) microbes. PRK lack membrane-bound organelles and a true nucleus; EUK possess them. Bacterial cell structure includes the CW (cell wall, peptidoglycan in bacteria, target for many antibiotics), CM (cell membrane), cytoplasm, ribosomes, nucleoid (circular chromosome), and often plasmids (extrachromosomal DNA conferring VRL or AMR). Some have capsules (polysaccharide, antiphagocytic), flagella (motility), or pili (adhesion, conjugation).

Bacterial growth occurs via binary fission, leading to exponential increase. Growth phases: lag, log (exponential), stationary, death. Optimal growth conditions vary by species (temperature, pH, oxygen requirements: obligate aerobes, anaerobes, facultative anaerobes). Nutritional requirements dictate culture media. Bacterial genetics involve chromosomal replication and HGT (horizontal gene transfer): transformation (uptake of naked DNA), transduction (phage-mediated transfer), and conjugation (plasmid transfer via sex pilus), all contributing to genetic diversity and AMR spread.

VRL enable pathogens to cause disease: adhesion factors (fimbriae, capsules), invasion factors (enzymes like hyaluronidase), exotoxins (secreted, e.g., neurotoxins, enterotoxins), endotoxins (LPS of Gram-negative bacteria, released upon lysis, potent IMM stimulator), and IMM evasion mechanisms. Antimicrobial agents (antibiotics) target specific bacterial processes: CW synthesis (penicillins, cephalosporins), protein synthesis (aminoglycosides, macrolides), nucleic acid synthesis (quinolones, rifampin), or CM function (polymyxins). AMR arises from enzymatic inactivation, target modification, efflux pumps, or reduced permeability, often plasmid-encoded.