4.2 Classification and Identification of Bacteria

The science of classifying and naming organisms is called

Taxonomy

Taxonomy involves?

Classification, nomenclature, identification

Classification

Assigning organisms to taxa based on similarities

Nomenclature

Rules for naming organisms

Identification

Determining that an isolated individual or population belongs to a specific taxon

Define taxon

Unit of organisms that taxonomists put together to form biological level classification

ex → family, genus, species, etc

How are organisms classified into taxa using the updated Linnaeus taxonomic categories (list from broadest to most specific)

Domain, kingdom, phylum, class, order, family, genus, species

Why doesn’t the definition of species as a group of organisms that can interbreed to produce viable offspring work for bacteria?

Bacteria reproduce asexually (binary fission), so they do not interbreed to produce offspring like sexually reproducing organisms.

What technology is driving many of the changes in how we classify organisms?

DNA sequencing technology allows scientists to compare genetic information and classify organisms based on their evolutionary relationships.

What is binomial nomenclature?

Scientific names, two word names: genus (capitalized) & species, written in italics

ex → Gray catbird = Dumetella carolinensis

What do the two parts of the scientific name represent?

Genus & species

Are viruses classified and named according to the same “rules” as living organisms?

Not living so classified differently

How are physical characteristics (be able to describe the morphology (shape and appearance) of both individual cells and colonies) used for bacteria identification?

Based on physical appearance of bacterial colony, size/shape of individual cells, presence/absence of features like endospores or flagella

What can be identified thru their physical characteristics under a microscope?

Protozoa, fungi, algae, and parasitic worms are often identified based on their morphology (shape)

How are differential stains used for bacteria identification? (be familiar with those from lab!)

Identify bacteria based on differences in their cell wall composition (e.g., Gram stain and acid-fast stain).

How are structural stains used for bacteria identification? (be familiar with those from lab!)

Identify specific bacterial structures (e.g., capsules, endospores, and flagella).

How are growth characteristics used for identification of bacteria?

By how and where they grow, including colony shape, color, size, oxygen requirements, and growth on different types of media.

How are biochemical tests (be familiar with those from lab!) used for bacteria identification?

Identify bacteria based on their metabolic activities and enzymes, such as their ability to break down sugars or produce certain substances.

*limited to organisms that can grow in culture, not immediate

Many biochemical tests require that microorganisms be cultured (or grown) in the lab for 12-24 hours. How might this affect the ability of physicians to diagnose infectious diseases?

Delays diagnosis and treatment because bacteria need time to grow.

How are serological tests used for bacteria identification?

Use antibodies to detect specific bacterial antigens, helping identify bacteria.

Define serology

Study of serum often refers to study of antigen-antibody reactions in lab

Define serum

Liquid portion of blood after clotting factors are removed

Explain how agglutination tests work

Type of serological test - antibodies bind to specific antigens, causing bacteria or particles to clump together, indicating a positive result.

How is phage typing used for bacteria identification?

Identifies bacteria based on which bacteriophages (viruses) can infect and kill them.

What are phages?

Viruses that infect & destroy bacteria → specific for their host bacteria

How is phage typing performed?

Bacterial lawn made on agar plate

Different bacteriophages with known spotted onto agar

Phage infects bacteria = plaque

Bacterial species identified when phage matched to known host

Bacteria identified based on which phages infect and kill them, creating clear zones (plaques).

What is a plaque?

A clearing where bacteria has been killed

How is nucleic acid analysis used for bacteria identification?

Identifies bacteria by analyzing and comparing their DNA or RNA sequences.

What techniques are used in nucleic acid analysis?

PCR, DNA sequencing (including 16S rRNA gene sequencing), and nucleic acid hybridization.

What bacterial gene sequence is often used for identification in nucleic acid analysis?

What is G+C content?

Amount of guanine & cytosine relative to adenine & thymine/uracil can be used to help identify organisms

What are taxonomic (dichotomous) keys and how are they used?

Series of paired statements worded so only one of two choices applies to any particular organism