Characterization of Microorganisms — Morphology, Metabolism, Genetics, Pathogenicity, Ecology, and Dichotomous Keys

A comprehensive set of practice flashcards covering key concepts from the lecture notes on characterization of microorganisms.

What defines the relationships among taxonomic groups and what kinds of characteristics are used to define microorganisms?

Taxonomic groups are defined by their similarities and relationships; characteristics include morphology (shape, size, arrangement, special structures), plus motility, staining reactions, chemical composition, cultural characteristics, metabolism, antigenicity, genetics, pathogenicity, and ecology.

What are the four morphological characteristics used to group bacteria?

Shape, size, arrangement, and special structures.

Which aspects are listed as separate topics under Morphology besides shape, size, and arrangement?

Motility and staining reactions.

What are the three well-known bacterial shapes, and what additional curved form is mentioned?

Coccus (spherical), Bacillus (rod-shaped), Spiral forms (Spirillum/Spirilla and Spirochete); Vibrio is a curved form.

Differentiate Spirillum, Spirochete, and Vibrio in terms of their motion/shape.

Spirillum: long, rigid spiral; Spirochete: spiral that bends during motion; Vibrio: curved rod like a comma.

What variations can cocci have beyond being perfectly round?

Cocci may be elongated, oval, or flattened on one side.

How may bacilli vary in shape and what are coccobacilli?

Bacilli may be short/thick; ends may be rounded, square, or concave; coccobacilli are short, thick rods resembling cocci.

What is a common curved bacterial form called?

Vibrio.

What is the typical size of a pathogenic bacillus?

Approximately 0.5 μm in diameter and 2 μm in length.

How do nonpathogenic bacilli typically compare in size to pathogenic bacilli?

They may be larger (about 4 μm in diameter and 20 μm in length).

What are the approximate dimensions of the smallest bacilli (coccobacilli)?

About 0.2 μm in diameter and 0.5 μm in length.

What are the size ranges for spirilla and cocci?

Spirilla: 1–14 μm in length; Cocci: 0.4–2 μm in diameter.

What general rule applies to bacterial size ranges within groups?

Each group has upper and lower size limits; the range is fairly constant, with environmental factors causing some variation.

What does the term diplococci describe?

Cocci that divide and form pairs.

What does the term streptococci describe?

Cocci that divide and cling end to end in chains.

What does the term staphylococci describe?

Cocci that divide irregularly to form grape-like clusters or broad sheets.

What are tetrad and sarcinae arrangements?

Tetrad: cocci in groups of four; Sarcinae: cubic packets of eight (no pathogenic cocci are found in this arrangement).

What do diplobacilli and streptobacilli refer to?

Diplobacilli: bacilli that occur in pairs; Streptobacilli: bacilli that occur in chains.

What is the snapping (Chinese lettering) arrangement?

Bacilli divide and bend at the point of division to form V-shaped arrangements randomly throughout the slide.

Explain slipping, palisade, and picket fence arrangements.

Slipping: cells sit side by side; Palisade: vertical alignment; Picket Fence: horizontal alignment; often due to a hinge at the ends.

What are the three special structures used to characterize microbes?

Capsules, Endospores, and Flagella.

Define a capsule.

A mucilaginous envelope surrounding many bacteria; formed by secreted slime; usually composed of polysaccharide.

What is an endospore and what is an exospore?

Endospore forms within the cell; when released, the structure is called an exospore; the vegetative cell is the non-spore form.

Why are endospores important and how many endospores can a cell produce?

Endospores are highly resistant survival structures; typically only one endospore is produced per cell.

What shapes can endospores take and how do their sizes relate to the cell?

Shapes: spherical, ellipsoidal, or cylindric; sizes are generally broader than the bacterial cell or not broader.

Where can endospores be located within a cell?

Central, subterminal, terminal, or paracentral locations.

How can the location and size of an endospore affect cell morphology?

Endospore location/size can change the appearance of the cell during sporulation.

Describe spindle-shaped and club-shaped endospores.

Spindle: endospore located centrally; club: endospore located at a pole; in some cases the endospore is broader than the vegetative cell.

What is a flagellum and what are common flagellar arrangements?

Flagella are fine hair-like surface appendages that propel the cell; arrangements include monotrichous, lophotrichous, amphitrichous, and peritrichous.

Define monotrichous, lophotrichous, amphitrichous, and peritrichous arrangements.

Monotrichous: single flagellum at one pole; Lophotrichous: a tuft at one pole; Amphitrichous: flagella at both ends; Peritrichous: flagella around the cell.

What types of motility are associated with specific structures?

Swimming (flagella), twitching (pili), and gliding (capsule production or membrane protein–driven mechanisms).

How does gliding motility typically occur?

Movement without flagella, often via secretion of polysaccharide slime or membrane-protein–driven mechanisms; can involve proton motive force.

What is a differential stain and which examples are mentioned?

A staining procedure whose action depends on chemical/physical differences; examples include Gram stain and Acid-fast stain.

How do Gram-positive and Gram-negative cell walls differ?

Gram-negative: cell wall contains lipopolysaccharide; Gram-positive: cell wall contains teichoic acids.

How can viruses be distinguished based on their nucleic acids?

Viruses are differentiated by whether their genome is RNA or DNA.

What are the two types of culture media and what do they signify?

Defined culture medium (known composition) and Complex culture medium (unknown composition).

What components are typically found in defined culture media?

Inorganic or organic components such as amino acids, sugars, purines, pyrimidines, vitamins, and coenzymes.

What ingredients are commonly found in complex culture media?

Ingredients with unknown composition such as yeast autolysate, blood cells, and blood serum.

What are the two physical growth requirements used to categorize organisms?

Temperature and atmospheric conditions.

Describe the temperature categories Thermophiles, Mesophiles, and Psychrophiles.

Thermophiles: grow at 55°C or higher (min ~45°C); Mesophiles: optimum 20–45°C (min ~20°C, max ~45°C); Psychrophiles: grow at 0°C with optimum ≤15°C and max ≤20°C.

Describe the atmospheric categories Aerobes, Anaerobes, and Capnophiles.

Aerobes require oxygen; Anaerobes require absence of oxygen; Capnophiles require elevated CO2.

What colony characteristics are used to describe growth on solid media?

Margin, color, elevation, texture, and shape.

What growth patterns are used to describe growth in a liquid medium?

Pellicle (surface film), ring (growth at surface margin), sediment (bottom), flocculent (loosely clumped), and turbid (cloudy).