Lecture 28: intro to microbiology

Overview of Microbiology

I. DefinitionStudy of microorganisms, small living organisms observable only via microscopes.

II. ScopeIncludes both pathogenic (disease-causing) and non-pathogenic microorganisms. Examples:

• Bacteria: Unicellular organisms, some of which can cause diseases while others are crucial for processes like fermentation and decomposition.

• Viruses: Acellular entities that require a host cell to replicate, can cause diseases ranging from the common cold to more severe infections like HIV and COVID-19.

• Fungi: Includes yeasts and molds; some species are pathogenic (e.g., Candida) while others (e.g., Penicillium) are used in antibiotic production.

• Algae: Photosynthetic organisms found in aquatic environments; while typically non-pathogenic, some species (e.g., red tide algae) can produce toxins harmful to humans and marine life.

• Protozoa: Unicellular eukaryotic organisms; can be pathogenic (e.g., Plasmodium causing malaria) or play essential roles in nutrient cycling.

• Helminths: Parasitic worms that can cause infections and diseases in humans and animals (e.g., tapeworms, roundworms), affecting the digestive system or other organs.

III. Importance of Studying MicrobiologyA. Relevance to HealthcareKnowledge about microorganisms is crucial for pharmacologists and pharmacists to understand diseases and develop treatments, including antibiotics, antivirals, and antifungals. Examples include:

• Antibiotics: Such as penicillin, derived from Penicillium fungi, effective against bacterial infections.

• Antivirals: Medications like oseltamivir (Tamiflu) used to treat influenza viruses.

• Antifungals: Such as fluconazole, used to treat infections caused by fungi.Understanding the lifecycle and pathogenic mechanisms of these organisms aids in effective drug design, such as targeting specific stages of a pathogen's life cycle.B. Contamination PreventionUnderstanding microbiology helps minimize contamination in pharmaceuticals, ensuring drug stability and safety for patients. Contaminated products, such as eye drops (e.g., Pseudomonas aeruginosa contamination), can lead to serious health risks, emphasizing the need for stringent microbial control in production environments. Knowledge of microbial growth and contamination control is essential in maintaining sterile conditions in healthcare settings and laboratories.C. Antibiotic ResistanceThere is an urgent need to develop new antibiotics due to rising antimicrobial resistance, an area with implications for treating common infections and surgeries. The misuse of antibiotics in healthcare and agriculture (e.g., adding antibiotics to livestock feed) has accelerated the emergence of resistant strains, making it imperative to investigate mechanisms of resistance (e.g., MRSA, multidrug-resistant TB).

IV. Microbial DiversityA. Types of Cells

• Prokaryotic: Smaller, unicellular organisms that reproduce asexually (binary fission). Lack membrane-bound organelles, including mitochondria and nuclei, which defines them as simpler in cellular organization.Examples: E. coli: A common bacterium that can be harmless or pathogenic, often used in genetic engineering. Staphylococcus aureus: A bacteria known for causing skin infections and food poisoning.

• Eukaryotic: Larger organisms that can be unicellular or multicellular and reproduce sexually or asexually. Contain membrane-bound organelles that compartmentalize their functions.Examples: Fungi: Such as Saccharomyces cerevisiae (baker's yeast), used in baking and brewing. Algae: Such as Chlorella and Spirulina, important for oxygen production and as dietary supplements.

V. Cell Structures in BacteriaA. Nuclear StructureContains nucleoid with circular, double-stranded DNA; plasmids may confer advantages such as antibiotic resistance or enhanced metabolism. Plasmids are often used in biotechnology for gene cloning and expression.B. Cell MembranePhospholipid layer; serves as a semi-permeable barrier for nutrients and energy, containing proteins that aid in transport and signaling. Responsible for various metabolic processes essential for survival.C. Cell WallProvides structure and protection; composed of peptidoglycan, a polymer made of sugars and amino acids. The cell wall's main function is to maintain the shape of the bacterial cell and prevent osmotic lysis (bursting due to influx of water).

• Gram-Positive Bacteria: Characterized by a thick peptidoglycan layer (up to 90% of the cell wall). Examples include Streptococcus pneumoniae, which can cause pneumonia and meningitis.

• Gram-Negative Bacteria: Thinner peptidoglycan layer (10-20%); has an outer membrane containing lipopolysaccharides (LPS). Examples include Escherichia coli O157:H7, known for causing foodborne illness, and Klebsiella pneumoniae, associated with hospital-acquired infections.

VI. Bacteria ClassificationA. Morphology

• Cocci: Spherical (e.g., Streptococcus, Staphylococcus).

• Bacilli: Rod-shaped (e.g., Bacillus subtilis, known for its role in soil nutrient cycling).

• Spirilla: Spiral-shaped (e.g., Helicobacter pylori, which causes stomach ulcers).

B. Gram StainingDifferentiates bacteria based on cell wall composition; influences antibiotic sensitivity, which is critical for determining treatment options. For example, Beta-lactam antibiotics are effective against Gram-positive bacteria but may be ineffective against Gram-negative due to the outer membrane barrier.

C. Biochemical TestsClassification of bacteria can also be done based on biochemical characteristics, such as:

• Metabolic pathways: Differentiating bacteria by their metabolic capabilities (e.g., lactose fermentation versus non-fermenter).

• Enzyme production: Identifying bacteria by specific enzymes they produce (e.g., urease, catalase).

• Nutritional requirements: Classifying based on growth factors required (e.g., fastidious versus non-fastidious organisms).

D. Genetic TechniquesModern classification incorporates molecular techniques such as PCR (polymerase chain reaction) and sequencing to analyze genetic material, allowing precise identification based on genetic similarities and differences. One particularly important genetic marker in bacterial phylogeny and taxonomy is the 16S ribosomal RNA (rRNA) gene sequencing.This gene is highly conserved among bacteria, meaning it has remained relatively unchanged throughout evolution, making it an excellent tool for determining relationships between different bacterial species.Through 16S rRNA gene sequencing, researchers can compare the genetic sequences from different organisms, helping to identify and classify new bacterial species, understand microbial community dynamics, and study evolutionary relationships. This method is powerful for environmental microbiology, clinical diagnostics, and exploring diversity in microbial ecosystems.

VII. Structures Contributing to VirulenceA. Capsule and Slime LayerAids in adhesion, protects from immune responses, and evades phagocytosis (e.g., Klebsiella pneumoniae can form a capsule that helps it resist being engulfed by immune cells).B. Fimbriae and PiliHair-like structures that enable bacteria to adhere to host tissues (e.g., Escherichia coli has fimbriae allowing it to attach to the urinary tract during infections). Pili also play a role in genetic material transfer (conjugation), contributing to genetic diversity and the spread of resistance genes.C. EndosporesDormant forms for survival in extreme conditions (e.g., Clostridium difficile can form spores that survive harsh environments and cause outbreaks in healthcare settings).

VIII. ConclusionMicrobiology plays a critical role in medicine, environmental science, and biotechnology. Addresses challenges like antibiotic resistance and infectious diseases, guiding advances in health and safety. Understanding microorganisms is vital for developing new treatments and for industrial applications in food production, sanitation, and waste management.