Classifying Microorganisms

Chapter 10

At what classification level does reproduction occur in animals/plants?

Species (successful reproduction occurs among the same species)

Why is classifying bacteria more difficult?

They reproduce sexually

Taxonomic rankings

Domain - kingdom - phylum - class - order - family - genus - species (broadest to most specific)

Are prokaryotes classified by rRNA or DNA sequences?

rRNA - mutations in rRNA are rare and detrimental

Which classification of microbes is the most diverse?

Bacteria

Nomenclature

Genus species strain (ex: escherichia coli K12 - a laboratory strain of E. coli)

Which parts of nomenclature are italicized?

Genus and species

What are the 4 methodology categories of identifying microorganisms?

1. Microscopy

2. Culture characteristics

3. Biochemical tests

4. DNA analysis

Morphology

A component of microscopy used to identify size and shape

Gram stain

A method used to identify the general type of bacteria

Is a gram stain sufficient to identify a bacterial species?

No - it is enough to start treatment but cannot be specific at a species level

Differential stain

Using multiple dyes to determine microorganism type (ex: acid fast stain)

Procedure for an acid-fast stain

1. Place the sample on a glass slide

2. Stain and heat the sample

3. Wash the sample with an acid solution

4. Apply another stain

5. Bacteria that hold onto the first dye are considered “acid-fast”

Culture characteristics include…

Pigment production, smell, and interaction with differential media

Hemolysis

The process of bacteria breaking down RBCs through toxins causing the release of cell contents

Biochemical tests

Use chemical reactions to identify characteristics of a microbe

Catalase test

Detects the presence of catalase through breakdown of hydrogen peroxide

pH indicator tests

Used to detect the change in pH within media; sugar fermentation (acidic) or urease producing ammonia (basic)

Dichotomous key

Used to identify microorganisms based on responses to biochemical tests (Gram stain, catalase test, etc.)