Bacterial classification

• The Universal Phylogenic Tree of Life: Analysis of 16 S rRNA sequences has yielded a universal evolutionary tree including viruses and prions.
• A microscopic organism may exist in its single-celled form or in a colony of cells and cannot be seen by naked eyes.
• Microorganisms can be classified using phenotypic classification systems such as morphological, anatomical, staining, cultural characteristics, nutrition, environmental factors, biochemical reactions, and antigenic structure.
• Genotypic classification systems include DNA-DNA hybridization and G+C content.
• Morphological classification of bacteria includes the three basic bacterial shapes: cocci, bacilli, and spirilla, with cocci being spherical or oval cells, bacilli being rod-shaped bacteria, and spirilla being curved bacteria which can range from a gently curved shape to a corkscrew-like spiral.
• Other shapes and arrangements of bacteria include filamentous bacteria, which are very long thin filament-shaped bacteria, some of which form branching filaments resulting in a network of filaments called 'mycelium'.
• The copper salt also gives color to the background, with the result that the cell and background appear dark blue and the capsule a much paler blue.
• Spores are commonly stained with malachite green or carbolfuchsin.
• The Capsule Stain is usually demonstrated by the negative staining procedure or a modification of it.
• The same impermeability then serves to prevent decolorization of the spore by a period of alcohol treatment sufficient to decolorize vegetative cells.
• One such “capsule stain” (Welch method) involves treatment with hot crystal violet solution followed by a rinsing with copper sulfate solution.
• Spores are most simply observed as intracellular refractile bodies in unstained cell suspensions or as colorless areas in cells stained by conventional methods.
• Nucleoids are stainable with the Feulgen stain, which is specific for DNA.
• The copper salt in the latter is used to remove excess stain because the conventional washing with water would dissolve the capsule.
• The spore wall is relatively impermeable, but dyes can be made to penetrate it by heating the preparation.
• The DNA-intercalating stains DAPI and ethidium bromide are widely used for fluorescence microscopy of nucleoids.
• Most bacteria are mesophilic and grow best at 30 - 37 ° C.
• The optimum temperature for growth of common pathogenic bacteria is 37 ° C.
• Star-shaped bacteria, rectangular bacteria, and pleomorphic bacteria that lack a rigid cell wall are examples of bacteria with different anatomical features.
• Based on their nutrition, bacteria can be categorized as autotrophs, which obtain their nutrition from inorganic compounds, and heterotrophs, which require organic sources of carbon such as sugars, fats and amino acids.
• Based on their cultural characteristics, bacteria can be categorized as fastidious, non-fastidious, hemolytic, non-hemolytic, and utilization of carbohydrates, oxidative, fermentative.
• Phototrophs absorb light energy, then utilize this in photosynthesis to create cellular energy.
• Gram’s Stain, Acid Fast Stain, and Extra growth factors requirements are methods used to identify bacteria based on their staining reactions.
• Capsule, flagella, fimbriae and pili, and spore formation are features of bacteria based on their anatomical features.
• Lithotrophs use reduced inorganic compounds as the electron donor (H-donor) in anaerobic or aerobic respiration.
• Most bacteria grow between pH 6.5 - 7.5.
• Thermophiles are heat lovers with a range of 50 - 60 ˚C and examples include Thermus aquaticus.
• Negative staining involves staining the background with an acidic dye, leaving the cells contrastingly colorless.
• Extremely thermophiles have a range of 250 ˚C and examples include Thermotoga maritima.
• Acidophiles thrive under highly acidic conditions (usually at pH 2.0 or below) and examples include Acetobacter aceti.
• Psychrophiles are cold lovers with a range of 15 - 20 ˚C and examples include Pseudomonas syringae.
• In peritrichous bacteria, the flagella form into bundles during movement, and such bundles may be thick enough to be observed on living cells by dark-field or phase-contrast microscopy.
• Neutrophiles thrives in neutral pH environments.
• Bacteria can be observed using various types of microscopy including simple staining, differential staining, preparing a smear, chemical fixation, alcohol physical fixation, heat, and negative staining.
• The peptidoglycan layer is composed of repeating disaccharide units that contain 4 amino acid groups attached to an O-C(CH3) unit.
• Mesophiles have a range of 30 - 37 ˚C and examples include E. coli.
• Alkaliphiles are capable of survival in alkaline (pH roughly 8.5 – 11) environments and examples include Thiohalospira alkaliphila.
• Acid-fast bacteria are colored red in primary stain and colorless in decolorizing agent.
• Gram positive cocci, gram negative bacilli, gram negative cocci, and gram positive bacilli are different types of bacteria.
• Bacteria can be classified into five main groups based on their oxygen requirements.