Microbiology Quiz on Bacterial Factors

Microbiology Lectures Semester-1

•  Course topics include bacterial cell structure, physiology, antibiotics and chemo, bacterial genetics, microbial resistance, microorganism host relationships, pathogenicity and virulence, complement system, inflammation, immune response, immunoglobulins, hypersensitivity, cells involved in immune response, and LP material.

Bacterial Cell Structure - Lecture 1

•  Bacteria are categorized by cell wall structure: rigid, flexible, and without a cell wall.
•  Rigid bacteria have dense cell walls and can form mycelia.
•  Flexible bacteria have thin cell walls.
•  Bacteria without cell walls, like Mycoplasma, lack cell walls.
•  Shapes and sizes of bacteria include cocci (spherical), streptococci and staphylococci (spherical), enterococci (oval), pneumococci (lanceolate), gonococci and meningococci (kidney-shaped), and bacilli (rod-shaped).
•  Bacterial arrangement depends on culture medium, age of culture, and division plan.
•  Examples of bacterial arrangements include clusters (staphylococci), chains (streptococci), and pairs (diplococci).
•  Some bacteria have a surrounding capsule, like pneumococci.

Bacterial Cell Structure - Additional Notes

•  Bacterial cells have constant structures like cell walls, cytoplasmic membranes, cytoplasm, ribosomes, inclusions, vacuoles, plasmids, pili, and capsules.

•  Gram-positive bacteria have thick cell walls containing peptidoglycan and teichoic acid.

•  Gram-negative bacteria have thin cell walls with an outer membrane containing lipopolysaccharides.

•  Protoplasts—bacterial cells without cell walls—are destroyed by lysosomes in hypotonic media.

•  Peptidoglycans are formed by the polymerization of NAM and NAG.

•  The cytoplasmic membrane is a double layer of phospholipids, with polar and non-polar layers. 

•  Mesosomes are invaginations of the cytoplasmic membrane and are involved in permeability and respiration.

•  The cytoplasm contains ribosomes (70S), RNA (16S and 23S rRNA), proteins, enzymes, lipids, pigments, carbohydrates, mineral salts, and water.

Ribosomes Role: Protein Synthesis

•  Protein synthesis occurs at the ribosomal level.
•  Genetic information is transcribed to mRNA, which is transported to ribosomes.
•  A complementary copy of the genetic code in DNA is made.
•  A segment of DNA that controls protein synthesis is called a cistron.
•  DNA → mRNA (transcription controlled by DNA polymerase).
•  mRNA carries genetic information for a single polypeptide chain (monocistronic in bacteria).
•  mRNA can carry the necessary information for multiple polypeptide chains (polycistronic in bacteria).
•  Translation (mRNA → polypeptide) requires the intervention of rRNA molecules (with anticodons).
•  UAA, UAG, and UGA are stop codons.

Inclusions

•  Inclusions appear in the cytoplasm at the end of active growth periods.
•  They are storage sites for nutrients (organic and non-organic).

Vacuoles

•  Vacuoles are spherical structures.
•  They contain various substances in aqueous solutions.
•  Some vacuoles have a lipoprotein membrane called a tonoplast.
•  Vacuoles may play a role in the buoyancy of aquatic bacteria.

Nucleus

•  The nucleus is directly in contact with the cytoplasm. 
•  It contains DNA and is rich in RNA.

Replication of the Bacterial Chromosome

•  Replication is semiconservative.
•  Meroploid is a condition with certain chromosomes being duplicated several times.
•  Polyploid is a condition with all chromosomes being duplicated several times.

Facultative Structures

•  The capsule is a fibrous matrix called glycocalyx.
•  Methods to highlight the capsule include methylene blue or India ink, and methods like Hiss stain.
•  The capsule provides virulence, resistance to surfactants and antibodies, adhesion to surfaces, protection against bacteriophages and protozoa, and contains substances with antigenic specificity.
•  Flagella are elongated, flexible formations involved in bacterial motility.
•  Flagella are composed of a single protein called flagellin.
•  Types of flagellation include monotrichous, lophotrichous, and peritrichous. - Fimbriae are short, thin formations involved in bacterial adhesion.
•  Spores are for resistance and conservation of the species.
•  Spores are resistant to heat, dryness, chemicals, antibiotics, and UV light.
•  Spores are formed and are common in Clostridium and Bacillus.

Bacterial Physiology

•  Water is the main component.
•  Water is free and bound to components.
•  Vacuoles store water.
•  Roles of water in bacteria: dispersion, reaction in metabolism, and as a final stage of oxidative reactions.
•  Roles of minerals: exchanges with the environment, regulation of osmotic pressure, stimulate growth and function of bacteria, and active enzyme systems.
•  Roles of carbohydrates in bacteria: intermediate metabolism, cell wall and capsule formation.

Chemical Constitution of Bacteria

•  Chemical components of bacteria include water (free and bound), minerals, carbohydrates, lipids, proteins, and pigments.
•  Water makes up 70–85% of bacterial volume.
•  Minerals are critical for many bacterial processes.
•  Carbohydrates provide energy and structural components.
•  Lipids contribute to the structural integrity of membranes.
•  Proteins carry out diverse functions essential for life.

Bacterial Metabolism

•  Bacterial nutrition involves sources of energy: photobacteria use light, and scotobacteria/chemosynthesizers use enzyme-catalyzed redox processes.
•  Autotrophic bacteria synthesize organic compounds from inorganic matter, and heterotrophic bacteria derive their organic matter from other substances.
•  Paratrophic bacteria derive their energy from host bacteria.

Bacterial Respiration

•  Respiration includes aerobic (in the presence of oxygen) and anaerobic (in the absence of oxygen) types.
•  Bacteria can be aerobic, anaerobic, facultative anaerobic, or microaerophilic, based on their oxygen requirements.

Metabolic Pathways

•  The main metabolic pathways (catabolism pathways) in bacteria include the hexo diphosphate pathway, pentose-monophosphate pathway, and Entner-Doudoroff pathway.
•  Lipid metabolism can be broken down into glycerol and fatty acids.
•  Protein degradation pathways include the transmission and deamination/decarboxylation of amino acids.

Cultivation of Bacteria

•  A clone is a population of bacteria arising from a single cell.
•  A strain is composed of descendants of a single isolate in pure culture.
•  Bacterial growth depends on temperature.
•  Mesophilic bacteria grow optimally at 30–37 °C.
•  Psychrophilic bacteria grow optimally at 20 °C.
•  Thermophilic bacteria grow optimally at 50–60 °C.
•  Extremophile/hyperthermophiles grow optimally at 80 °C.

Culture Media

•  Artificial media must be nutritious, sterile, have certain osmotic pressure, and have favorable humidity.
•  Some bacteria need specific growth factors (auxotrophs).
•  Elective media support the growth of specific bacteria.
•  Enrichment media permit the development of particular pathogens while inhibiting the growth of other organisms.
•  Selective media inhibit the growth of all but the organism of interest.
•  Differential media show the growth or metabolic differences between microbes in a culture or a colony

Isolated Colony

•  Bacteria can be isolated through streak plate methods.
•  A colony is the totality of bacteria resulting from the multiplication of a single cell.
•  A colony is also termed the isolate and represents the bacterial clone.

Bacterial Growth Curves

•  Phases of growth include lag, log, stationary, and death. 
•  Lag phase—no increase in number of living bacterial cells—depends on size of inoculum.
•  Log phase/exponential phase—increase in number of bacterial cells—is critical.
•  Stationary phase—plateau in growth—is reached when nutrient supply diminishes.
•  Death phase—exponential population decline—is caused by depleted nutrients.

Appearance of Cultures on Solid Media

•  Smooth colonies have a homogenous appearance.
•  Rough have a non-homogenous appearance.

Action of Physical, Chemical and Biological Factors on Bacteria

•  Antisepsis removes microbial vegetative forms like those on membranes of skin or mucous membranes.Disinfection destroys microbial vegetative forms on surfaces or in environments.

•  physical factors: high/low temperature, filtration, non-ionizing (UV) or ionizing (X) radiation, ultrasounds, osmotic pressure

•  chemical factors: disinfectants, antiseptics

• High temperature methods :Dry heat, Moist Heat, Incanration, incineration, Red heat, autoclaving, Tyndallization, pasteurization, and boiling.

• Low Temperature methods: Slow freezing, Sudden freezing and lyophilization

Enzymes

•  Bacterial enzymes are classified by their site of action: extracellular (hydrolases), intracellular, and ectocellular enzymes.
•  Constitutive enzymes are always present, and inducible enzymes are produced in response to specific substrates.

Substances with Antibiotic Action

•  Some bacteria produce bacteriocins such as colicins which inhibit other bacterial strains.
•  Polypeptide antibiotics are produced by Bacillus bacteria.

Bacterial Vitamins

•  Vitamins like biotin, thiamin, riboflavin, and other B vitamins are found in bacteria.

Growth factors

•  Bacteria, like humans, require essential factors for growth such as vitamins and sometimes amino acids.

Microbial Genetics

•  Bacterial genetic material can be modified by adding, losing, substituting, or reversing genetic material.
•  Bacterial DNA contains base pairs in a double helix at room temperature.
•  High temperatures cause denaturation to uncoil the double helix of bacteria.
•  The process of denaturation and renaturation can serve as a method for studying bacterial DNA.

Bacterial Genome

•  Genotypes and phenotypes describe an organism’s genetic components and observable characteristics.
•  Replicons include bacterial chromosomes, plasmids, and bacteriophage genomes.
•  Essential genes are needed for basic bacterial function, and extrachromosomal accessory genes are often involved in antibiotic production and other beneficial or harmful conditions.

Plasmids

•  Plasmids are extrachromosomal genetic elements.
•  They have the ability for independent physical replication.
•  They can be circular or linear.
•  They contain genetic information that’s not essential for bacterial survival.
•  They are transmitted from one generation to another.
• R plasmids confer antibiotic resistance.
• Col plasmids are responsible for the production of bacteriocins (antibiotics).
• F factors, also known as sex factors, control processes involved in bacterial conjugation.

Transposable Genetic Elements

•  Transposable genetic elements can be inserted sequences (IS) or transposons (Tn).
•  IS elements do not contain any genes, while Tn elements do contain genes.
•  Bacteriophages are viruses that infect and replicate bacterial cells.

Mechanisms of Bacterial Variability

•  Phenotypic variability—morphological or physiological changes—is not inherited.
•  Genotypic variability—permanent changes in genetic material—includes mutations and genetic transfer.
•  Mutations are caused by accidental changes in nucleotide sequences.
•  Genetic transfer methods are: transformation, transduction, and conjugation.

Microbial Resistance

•  For an antibiotic to inhibit a bacterium, it must reach a target at a sufficient concentration and not be inactivated before binding.
•  Resistance can be natural (genetically determined) or acquired (usually due to subpopulation changes in an environment).

Biochemical Mechanisms of Resistance

•  Resistance mechanisms include production of enzymes to inactivate antibiotics, decreased permeability of the cytoplasmic or membrane, excessive production of complementary enzymes, or alteration of intracellular targets.

Acquired Resistance

• Resistance can result from single or multiple-step mutations.

Types of Resistance

•  Monovalent—resistance to a single antibiotic.
•  Multivalent—resistance to multiple antibiotics.
•  Excessive or inappropriate antibiotic use is a primary reason for resistance.

Pathogenicity and Virulence

•  Pathogenicity is the ability to cause disease, and virulence describes the degree of pathogenicity of a bacterial strain.
•  Factors that condition pathogenicity and virulence include multiplication and invasiveness and the production of toxins.

Somatic Factors that Allow Multiplication and Invassiveness

•  Pili, lectins, ligands, glycocalyx, capsules, adhesins, components of the bacterial wall (e.g., proteins M and O antigens), and polysaccharide A (teichoic acids) are involved in mediating cell-to-cell interactions and facilitating colonization.

•  Soluble factors include coagulase, leukocidin, substances that increase intracellular cAMP concentration/function (e.g., various enzymes such as catalase, glutathione peroxidase, superoxide dismutase, and certain cytochrome oxidases), production of factors that resist lysosomes, and specific enzymes that damage host cells (e.g., collagenase, lecithinase). 

Multiplication and Toxin Genesis (Exotoxins and Endotoxins)

•  Exotoxins are proteins produced and secreted by bacteria during their growth cycle(plasmid encoded protein structures); they are highly toxic and immunogenic.
•  Endotoxins are toxic components of the bacterial cell wall; they are not easily inactivated and are less immunogenic.

Organism's Defenses Against Infections

•  Cutaneous-mucosal anatomical barriers (skin, mucous membranes, saliva, mucus, tears) protect against pathogen entry.
•  Organ barriers, such as the blood-brain barrier, respiratory tract, digestive tract, and genitourinary tract, also help prevent pathogen spread and multiplication.
•  Lymph nodes and phagocytic systems are important to manage pathogens.

Complement System

•  Complement systems are non-specific defenses that combat infections.
•  These systems eliminate immune complexes or apoptic cells.
•  Three pathways activate the complement system: classical, lectin, and alternative.

Immunity

•  Immunity is of two major classes: innate and adaptive immunity; Innate is non-specific, and adaptive is specific.

Humoral Immune Response

•  Production of antibodies (Abs) and elimination of antigens (e.g., bacteria, viruses, toxins) are major functions.
•  After an initial exposure to an antigen, a primary immune response occurs, characterized by a slow response with immunoglobulin M (IgM) production.
•  A secondary response—following subsequent exposures to the same antigen—exhibits a quick production of IgG antibodies as a result of memory cells. 

Cellular Immune Response

•  Cellular immune responses involves the cell-mediated process of lymphocyte activation and proliferation for eliminating pathogens.
•  T-helper (Th) and cytotoxic T (Tc) cells are essential in these responses.
•  Other involved cells include macrophages, dendritic cells, and natural killer (NK) cells.

Vaccines

•  Vaccines are suspensions of inactivated microorganisms or their components used to stimulate the immune response and provide immunity.
•  Vaccines are classified based on the preparation technique and target antigens.
• Types include Bacterial, Viral, Monovalent (Single-Target), and Associated (Combines).

Immunoglobulin Classes

•  Immunoglobulin classes (IgA, IgD, IgE, IgG, and IgM) have different functions and characteristics based on their ability to cross the placenta and interact with various immune cells and responses.

Hypersensitivity

•  Hypersensitivity describes states of increased reactivity induced by repeated exposure to antigens.

•  Four types of hypersensitivity reactions are classified based on the mechanisms and immune responses involved: Type I (anaphylactic—immediate reaction), Type II (cytotoxic—antibody-mediated cell destruction), Type III (immune complex—antigen-antibody complex deposition), and Type IV (cell-mediated/delayed type).

Bacterial Classification

•  Bacteria can be Gram-positive or Gram-negative based on cell wall characteristics.
•  Oxygen requirements classify bacteria as aerobic, anaerobic, facultative anaerobic, or microaerophilic.

Questo quiz testa la tua conoscenza sui fattori somatici, antibiotici e virulenza associata ai batteri. Rispondi correttamente alle domande riguardo i meccanismi di invasività e protezione delle batterie. Metti alla prova le tue competenze in microbiologia con queste domande mirate.