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BIOLOGIA DEI MICRORGANISMI
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This document comprehensively covers key concepts in microbiology, starting with the classification and general characteristics of microorganisms (bacteria, archaea, viruses, eukaryotic microbes). It details the intricate structures of bacterial cells, including cell walls (Gram-positive/negative distinctions), membranes, flagella, fimbriae, and internal components like plasmids and inclusions. Viral biology is thoroughly explained, focusing on structure, replication cycles in animal cells and bacteriophages (lytic and lysogenic), and the Baltimore classification. The notes also delve into microbial metabolism, categorizing organisms by carbon and energy sources, and their oxygen requirements. Essential methods for microbial identification and growth in laboratory settings are described, alongside microbial interactions, virulence factors, and antibiotic mechanisms of action and resistance. Finally, it elaborates on bacterial gene transfer mechanisms: transformation, conjugation, and transduction.
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- **Microorganisms Overview:**
- Defined by their microscopic size, primarily unicellular.
- Classified into prokaryotic (bacteria, archaea) and eukaryotic (fungi, algae, protozoa).
- Viruses are obligate intracellular parasites, not considered living cells.
- Historical context: Pasteur disproved spontaneous generation; Koch's postulates defined disease causality; Woese's three-domain classification.
- **Bacterial Cell Structure:**
- **External Structures:** Capsules (adhesion, anti-opsonization), Fimbriae/Pili (adhesion, conjugation), Flagella (motility, chemotaxis).
- **Cell Wall:** Composed of peptidoglycan (NAM, NAG). Gram-positive bacteria have a thick peptidoglycan layer with teichoic acids; Gram-negative bacteria have a thinner peptidoglycan layer, an outer membrane with LPS (Lipid A, polysaccharides), and porins. Mycoplasmas lack cell walls. Archaea have diverse cell wall types, some with pseudopeptidoglycan.
- **Cytoplasmic Membrane:** Lipid bilayer (phospholipids, no cholesterol in bacteria, some opanoids), proteins. Functions include permeability, energy generation, and chemotaxis.
- **Internal Structures:** Nucleoid (bacterial chromosome), Plasmids (extrachromosomal DNA, carry advantageous genes), Ribosomes (protein synthesis), Inclusions (storage for energy, gas vacuoles for buoyancy, magnetosomes for orientation).
- **Viral Biology:**
- **Structure:** Virions consist of genetic material (DNA or RNA, single or double-stranded, linear or circular) encased in a protein capsid (helical or icosahedral symmetry). Some viruses also have an outer lipid envelope.
- **Replication Cycle:** Involves adsorption, penetration, uncoating, genome replication, protein synthesis, assembly, and release (via lysis or budding).
- **Baltimore Classification:** Groups viruses based on their nucleic acid type and replication strategy to produce mRNA.
- **Bacteriophages:** Engage in lytic cycles (host cell destruction) or lysogenic cycles (phage DNA integration into host chromosome). They are mediators of transduction.
- **Microbial Metabolism & Ecology:**
- **Carbon Sources:** Autotrophs (CO2), Heterotrophs (organic compounds).
- **Energy Sources:** Chemotrophs (chemical oxidation), Phototrophs (light).
- **Oxygen Requirements:** Aerobes, Anaerobes, Facultative anaerobes, Microaerophiles, Aerotolerant.
- **Environmental Factors:** Temperature (psychrophiles, mesophiles, thermophiles, hyperthermophiles), pH, and pressure (barotolerant, barophilic) influence growth.
- **Microbial Growth & Identification:**
- **Growth Curve:** Lag, exponential (log), stationary, and death phases describe population dynamics.
- **Culture Media:** Liquid (broths) or solid (agar); minimal or complex; enriched, selective, or differential for specific purposes.
- **Identification Techniques:** Gram staining, Ziehl-Nielsen staining, FAME analysis, DNA-DNA hybridization, 16S rRNA sequencing, and metagenomics.
- **Microbial Interactions & Pathogenesis:**
- **Interactions:** Include synergy, competition, commensalism, mutualism, and parasitism.
- **Virulence Factors:** Adhesins, enzymes, and toxins (exotoxins: cytotoxic, neurotoxic, enterotoxic; endotoxins: LPS Lipid A in Gram-negatives) contribute to pathogenicity.
- **Antimicrobial Strategies:** Sterilization (complete removal), disinfection (partial removal of pathogens). Antibiotics exert selective toxicity by targeting unique microbial processes.
- **Antibiotic Resistance:** Can be natural or acquired through mutation or horizontal gene transfer (transformation, conjugation via plasmids, transduction via phages). Mechanisms include target modification, enzymatic inactivation, efflux pumps, and reduced permeability.
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