Microbio Exam 1 Flashcards
- Robert Koch
Robert Koch was a pioneering German physician and microbiologist known for his significant contributions to the field of microbiology, including the development of Koch’s Postulates.
Koch’s Postulates
4 critera used to determine whether a specific microorganism is the cause of a particular disease
Petri Dish
A Petri dish is a shallow, flat, cylindrical, lidded dish made of glass or transparent plastic. It is commonly used in laboratories for the cultivation and observation of microorganisms.
Plate Streaking (for Isolation)
Plate streaking is a microbiological technique used to isolate individual bacterial colonies from a mixed culture. It involves streaking a sample onto the surface of an agar plate to obtain separate colonies.
Media (Solid and Liquid)
Media, in microbiology, refer to substances or environments that provide nutrients and support the growth of microorganisms. They can be in either solid (agar) or liquid (broth) form.
Agar vs. Gelatin
Agar keeps form at 37C, while gelatin liquifies
This is the temp of incubation
Agar has more complex carbohydrates, which are more difficult for microbes to break down
Broth
Broth is a liquid medium used for the growth and cultivation of microorganisms. It provides a nutrient-rich environment to support microbial growth in suspension.
Differential Media (with Examples)
media contains specific indicators or substrates that allow different species of microorganisms to make distinct visible reactions. Examples include Blood Agar and MacConkey Agar.
Blood agar is a good differential medium because of the hemolytic activity on red blood cells.
Selective Media (Selection Methods)
Selective media are culture media designed to inhibit the growth of certain microorganisms while allowing the growth of others. Selection is achieved through the inclusion of specific chemicals or factors.
Complex Media
-composed of extracts, digests, or infusions from biological sources.
-support a wide range of microbes
Nutrient Media
Nutrient media are culture media that provide essential nutrients required for the growth of a variety of microorganisms. They are often used for general-purpose culturing.
Transport Media
Transport media are specialized media used to maintain the viability of clinical specimens during transport from the collection site to the laboratory. They help preserve the integrity of the sample.
Brightfield Microscopy
-specimens are viewed against a bright background.
-stained or unstained samples
Darkfield Microscopy
-oblique lighting to create contrast by illuminating specimens against a dark background.
-observes live, unstained specimens.
Phase Contrast Microscopy
enhances the contrast of transparent, unstained specimens by exploiting differences in the phase of light passing through the specimen.
Fluorescence Microscopy
Uses fluorescent dyes or proteins to label specific molecules or structures within a sample.
It enables the visualization of specific targets with high sensitivity.
Electron Microscopy
Advanced microscopy technique that uses a beam of electrons instead of visible light to achieve much higher resolution and magnification, allowing for detailed examination of subcellular structures.
Differential Stain
A differential stain is a staining technique that differentiates between different types of microorganisms or cellular structures based on their staining properties. The Gram stain and acid-fast stain are examples.
Gram Stain
The Gram stain is a widely used differential staining technique that classifies bacteria into Gram-positive and Gram-negative groups based on differences in cell wall composition.
Acid-Fast Stain
The acid-fast stain is a differential staining technique used to identify acid-fast bacteria, such as Mycobacterium species, which have a unique cell wall composition that resists decolorization during staining.
Cultivability of Microorganisms (Limitations of Microbial Culture)
Not all microorganisms can be easily cultured in the laboratory. Some require specific growth conditions or are uncultivable due to complex nutritional needs or symbiotic relationships.
Isolation of Organisms from Colonized Sites of the Body
Can be challenging due to
- Ethical concerns
- Complex Microbial Ecosystems
- Rely on culturing on artificial media, which can be biased. The body is far different than media is
Sterile Sites of the Body
Certain body sites, such as the bloodstream, cerebrospinal fluid, and internal organs, are normally sterile, meaning they should not contain microorganisms under healthy conditions.
Use of Media for Growth (Nutrient), Isolation (Selection), and Identification (Differential)
Nutrient media supports growth
Selective media inhibit unwanted microorganisms
Differential media help identify specific characteristics.
Limits of Resolution for Light Microscopy (Function of the Wavelength of Light)
The resolution of light microscopes is limited by the wavelength of visible light. Objects closer together than half the wavelength cannot be distinguished as separate.
Use of Acidic vs. Basic Stains (Use of Negative Staining)
Acidic stains (e.g., nigrosin) are repelled by bacterial cells, creating a dark background for visualization. This is the initial step in gram staining.
Basic stains (e.g., crystal violet) adhere to cells, providing contrast.
Brightfield vs. Darkfield Microscopy (Technique and Uses)
Brightfield microscopy uses transmitted light for standard observation, while darkfield microscopy employs oblique lighting to visualize transparent specimens like live bacteria.
Gram Stain vs. Acid-Fast Stain
Gram staining classifies bacteria into two broad groups based on cell wall characteristics (Gram-positive and Gram-negative),
Acid-fast staining specifically targets and identifies acid-fast bacteria with unique cell walls, such as Mycobacterium species.
Shape and Arrangement of Bacteria
Bacteria exhibit diverse shapes
cocci (spherical), bacilli (rod-shaped), and spirilla (spiral-shaped)
and arrangements (e.g., chains, clusters) that aid in their identification and classification.
Bacterial Culture Considerations (Temperature, Oxygen, Nutrients)
Bacterial culture success depends on factors like temperature (mesophilic, thermophilic), oxygen requirements (aerobic, anaerobic), and nutrient availability.
The Germ Theory of Disease and Its Relationship to Microscopy, Spontaneous Generation, Fermentation, and Koch’s Postulates
The Germ Theory of Disease revolutionized our understanding of infectious diseases. It built upon:
Advances in microscopy, which allowed scientists to observe microorganisms.
The refutation of spontaneous generation, the idea that life could arise from nonliving matter.
The understanding of fermentation as a microbial process.
Koch’s Postulates, which provided a framework for establishing the causal link between specific microorganisms and diseases. Koch’s work with anthrax and tuberculosis were pioneering examples.
Implications for Microbial Contamination in Various Body Locations
Different body locations have varying levels of microbial contamination:
Sterile sites (bloodstream, internal organs) should be free of microorganisms under healthy conditions.
Understanding contamination levels is crucial for:
Choosing appropriate lab techniques and culture media.
Isolating pathogens without interference from normal microbiota.
Identifying microbes in clinical samples accurately.
Peptidoglycan and Outer Membrane Structure (in Detail)
Peptidoglycan is a fundamental component of bacterial cell walls. Important details:
Gram-positive bacteria have a thick peptidoglycan layer.
Gram-negative bacteria have a thinner peptidoglycan layer and an outer membrane.
Outer membrane contains lipopolysaccharides (LPS), which are significant for immune responses and antibiotic resistance.
Bacterial Structures: Common to All Bacteria, Identification Aids, and Virulence Factors
Common structures include:
Cell wall, cytoplasmic membrane, cytoplasm, ribosomes, DNA.
Identification structures like flagella, pili, capsules, or spores.
Virulence factors, such as toxins, adhesins, and invasins, facilitate disease.
Parameters Defining a Bacterial Niche and Their Effects on Microbial Growth
Bacterial niche parameters include:
Temperature, pH, oxygen availability, nutrient sources, and competition.
Manipulating these conditions impacts:
Microbial growth, with temperature extremes causing reduced growth or death.
Adaptation to different environments and niches.
Comparison of Aerobic and Anaerobic Energy Metabolism
Differences between aerobic and anaerobic metabolism:
Aerobes use oxygen as the final electron acceptor in the electron transport chain, yielding more energy.
Anaerobes use alternative electron acceptors (e.g., nitrate, sulfate) or fermentation, yielding less energy.
Implications for energy production and adaptation to oxygen availability.
Comparison of Respiration vs. Fermentation
Respiration uses electron transport chains and can yield a higher amount of ATP, while fermentation relies on substrate-level phosphorylation (where ATP is synthesized directly) and produces less ATP.
The end products of these pathways differ. In respiration, the final electron acceptor is usually oxygen, leading to the production of water. In fermentation, the end products vary depending on the specific type of fermentation but do not involve the complete oxidation of glucose.
Respiration is more efficient in terms of energy generation per molecule of glucose, making it the preferred energy production pathway when oxygen is available. Fermentation is typically used by cells when oxygen is scarce or absent, despite its lower energy yield.
Cell Membrane
Also called plasma membrane
Phospholipid bilayer that surrounds the cell’s cytoplasm. Selevely permeable barrier, controlling entry/exit of ions, nutrients, waste.
Lipid Bilayer
The lipid bilayer consists of two layers of phospholipid molecules arranged in such a way that their hydrophobic tails are oriented inward while their hydrophilic heads face outward. This structure creates a dynamic and flexible membrane where various proteins, including transporters, receptors, and enzymes, are embedded. The lipid bilayer’s fluidity allows the membrane to adapt to changing conditions.
Semipermeable/Diffusion/Transport
A semipermeable membrane selectively allows certain substances to pass while restricting others based on factors such as size, charge, and solubility. Diffusion is the passive movement of molecules or ions from regions of higher concentration to lower concentration until equilibrium is reached. Transport, whether passive (facilitated diffusion) or active (active transport), involves the movement of specific molecules across the membrane through various mechanisms.
Cell Wall
The cell wall is a rigid and protective outer layer found in bacterial, plant, and fungal cells. In bacteria, it lies outside the cell membrane and contributes to cell shape, structural integrity, and protection against osmotic pressure. The composition and structure of the cell wall vary between bacterial groups, such as Gram-positive and Gram-negative bacteria.
Peptidoglycan
Peptidoglycan is a complex polymer found in the cell walls of most bacteria. It consists of repeating units of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) linked together, forming glycan chains. These chains are crosslinked by peptide bridges, creating a strong, flexible mesh-like structure surrounding the bacterial cell membrane.
NAG/NAM
N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) are sugar molecules that form the backbone of peptidoglycan in bacterial cell walls. They are connected in alternating fashion, creating the glycan chains of peptidoglycan.
Tetrapeptide Crosslinks
Tetrapeptide crosslinks are chemical bonds that connect the peptide chains of peptidoglycan strands in the bacterial cell wall. These crosslinks consist of four amino acids: L-alanine, D-alanine, D-glutamic acid, and meso-diaminopimelic acid (meso-DAP), or diaminopimelic acid (DAP).
Penicillin
Penicillin is a class of antibiotics that inhibits bacterial cell wall synthesis by targeting the enzymes involved in peptidoglycan crosslinking. It weakens the cell wall, making bacteria susceptible to osmotic lysis and cell death.
Lysozyme
Lysozyme is an enzyme found in various bodily secretions, such as tears and saliva, as well as in some immune cells. It targets and breaks down the peptidoglycan structure of bacterial cell walls.
Gram Negative / Gram Positive
Bacteria are classified into two major groups based on their response to the Gram stain. Gram-negative bacteria have a thinner peptidoglycan layer and an outer membrane, while Gram-positive bacteria have a thicker peptidoglycan layer but lack an outer membrane.
- Connection: Gram staining is a fundamental microbiological technique used to differentiate between these two groups based on cell wall characteristics.
Teichoic Acid
Teichoic acids are negatively charged polymers found in the cell walls of Gram-positive bacteria. They contribute to the overall negative charge of the cell surface and play roles in cell structure, adhesion, and ion transport.
Outer Membrane
The outer membrane is a distinctive feature of Gram-negative bacteria and forms an additional protective layer outside the thin peptidoglycan layer. It contains various proteins and lipopolysaccharides (LPS).
Lipopolysaccharide (LPS)
LPS is a major component of the outer membrane in Gram-negative bacteria. It consists of lipid A, a core oligosaccharide, and an O polysaccharide chain. Lipid A is responsible for the endotoxic properties of LPS.
