Bacterial Classification Flashcards

Taxonomy Basics

• Taxonomy consists of three main components: classification, identification, and nomenclature.
• Classification is the systematic arrangement of organisms into groups based on similarities and relationships.
• Taxon is the singular term for a taxonomic group, while taxa is the plural form.
• Identification involves determining if an organism belongs to an established taxon or if it represents a new species.

Identification Process

• The identification process practically applies classification criteria to differentiate organisms, verify strains, and isolate disease-causing organisms.

Nomenclature

• Nomenclature refers to the assignment of names to various taxa following established international rules.

Characteristics for Classification

• Bacteria are classified using phenotypic, analytic, and genotypic characteristics.
• Phenotypic characteristics include microscopic morphologies, macroscopic morphologies, and growth/biochemical features.

Phenotypic Methods

• Common phenotypic classification methods include biotyping, serotyping, antibiogram patterns, and phage typing.

Analytic and Genotypic Characteristics

• Analytic traits consist of cell wall fatty acids, whole cell lipids, proteins, and enzymes.
• Genotypic characteristics involve genome size and the guanine plus cytosine ratio.
• Genotypic techniques for classification include DNA hybridization, nucleic acid sequence analysis, plasmid analysis, ribotyping, and chromosomal DNA fragment analysis.

Goals of Classification

• The ultimate aims are to gather information, evaluate results relative to one another, and draw meaningful conclusions.

Macroscopic Appearance of Bacterial Colonies

• Characteristics to identify bacteria from colony appearance include size, shape, elevation, edge appearance, optical features, pigmentation, haemolytic properties, swarm behavior, and autofluorescence.

Defining Colonies

• A colony is a visible collection of bacterial or fungal cells of a single species growing on solid medium.
• Colony Forming Unit (cfu) is a term used to denote the number of viable cells in a sample.

Colony Formation

• Bacterial colonies originate from a single bacterial or fungal cell, not from groups of cells proliferating together.

Colony Types

• Various colony forms include circular, irregular, filamentous, and rhizoid shapes.
• Elevations can be categorized as raised, convex, flat, umbonate, or cateriform.
• Colony margins can be entire, undulate, filiform, curled, or lobate.

Biochemical Markers

• The identification of bacteria often relies on biochemical markers, which are measurable traits indicating the presence or absence of specific substances.

Routine Biochemical Tests

• Common biochemical tests include oxidase, nitrate reduction, amino acid degrading enzymes, and carbohydrate fermentation/utilization.

Specific Biochemical Tests

• Specific tests like the coagulase test are used for staphylococci, while the pyrrolidonyl arylamidase test is employed for Gram-positive cocci.

Serotyping

• Serotyping is a reliable method for identifying organisms that are inert in biochemical testing, hard to culture, associated with specific diseases, or require rapid identification.

Antigen Representation

• Different antigens are represented by specific letters: cell wall (O), flagellar (H), and capsular (K).