Bacterial Classification and Morphology

Question 1

Eukaryotic

Answer 1

All organisms, microscopic and macroscopic, except bacteria and blue green algae

• true nucleus
• histones
• diploid
• sexual and asexual
• no cell wall
• 80S
• mitochondrial membrane for electron transport
• sterols present in cytoplasmic membrane

Question 2

Prokaryotic

Answer 2

Simpler cell types

• 0.3-0.2 um in diameter
• supercoiling
• haploid
• asexual
• cell wall with murein
• 70S
• cytoplasmic membrane for electron transport
• sterols absent

Question 3

Why are differences between prokaryotes and eukaryotes important?

Answer 3

Reveal their different strategies for survival
- eukaryotes: adaptation and specialization
- prokaryotes: divide and conquer
Allow antimicrobials targeting unique bacterial structures

Question 4

Fungi

Answer 4

Eukaryotic, multicellular, but similar to bacteria in complexity without differentiation into specialized tissues and organs
- all cells remain simple and similar, despite remaining permanently attached in a large organism

Question 5

Bacterial nomenclature

Answer 5

Classical binomial Linnean system

• species and genus name
• number of species may be included in a genus
• first word is the genus name and is always capitalized
• second word is species name and is not capitalized

Question 6

Taxonomy

Answer 6

System of classification that groups bacteria with similar properties and is used to distinguish those that are different

Question 7

Species

Answer 7

Basic taxonomic unit

• bacterial species are not equivalent to eukaryotic species, since bacteria are haploid and produce asexually!
• prokaryotes: species is defined as a group of strains with unique phenotypic properties and exhibit more than 70% whole genome DNA-DNA hybridizations among strains

Question 8

Bacterial strain

Answer 8

Consists of descendants from a single isolate in pure culture (a clonal population)
- type strain: originally described isolate of the species

Question 9

Is sexual reproduction used as a criterion for classification of bacteria?

Answer 9

NO

Question 10

Polyphasic taxonomy

Answer 10

Uses combined systems of DNA sequence and phenotypic characteristics

Question 11

DNA sequence

Answer 11

• DNA-DNA hybridization (70%)
• 16S rRNA sequence (97%)
• Multilocus sequence typing
• Average nucleotide identity (95%)

Question 12

Phenotypic characteristics

Answer 12

• chemical analyses of structural components
• serologic reactivity
• enzyme profile
• nutritional requirements
• morphology

Question 13

Keys

Answer 13

Used in clinical laboratory to classify bacteria into convenient groups of clinical interest

• uses biochemical reactions, sugar fermentations, etc
• useful in identifying bacteria quickly with little materials

Question 14

Tree of Life

Answer 14

• archebacteria (archea): extremophilic environmental bacteria
• eubacteria (true bacteria)
• eukaryota

Question 15

Eubacteria are phenotypically divided based on

Answer 15

• cell envelope type: gram positive or negative
• cell morphology: cocci, bacilli, spirilla
• motility
• multiplication: binary fission, budding, etc
• cell association
• dependence on living cells for growth
• atmospheric requirements

Question 16

Cell association

Answer 16

• long chains: streptococci
• clusters: staphylococci
• cubical packets of 4 or 8: tetrads or sarcinae
• pairs: diploccoci or diplobacilli (are always end to end, not on top of each other)

Question 17

Obligate requirements

Answer 17

Require oxygen, oxidize only, respire

- stick to the top layer of a test tube

Question 18

Obligate anaerobes

Answer 18

Killed by oxygen, ferment only or use anaerobic respiration

• still respire but use an electron carrier that is not oxygen
• stick to bottom of tube

Question 19

Faculative anaerobes

Answer 19

Could oxidize or ferment

• prefer to grow aerobically
• mostly stick to the top, but distribute throughout the tube

Question 20

Microaerophilic

Answer 20

Require reduced oxygen

- stick a little below the top

Question 21

Aerotolerant

Answer 21

Do not require oxygen, not killed by oxygen, ferment only

- are evenly distributed throughout the tube

Question 22

Capnophilic

Answer 22

Require increased carbon dioxide

Question 23

Microscopy

Answer 23

Most common units of measurement are the micron or micrometer (10^6 m) or nanometer (10^9 m)

Question 24

Light microscope

Answer 24

Bright field, staining required

• max resolving power of 0.2 um under optimal conditions
• 1000 X magnification commonly used with oil immersion

Question 25

Darkfield and phase contrast microscopy

Answer 25

Used to observe unstained, living cells and movement | - resolution to 0.1 um

Question 26

Fluorescent microscopy

Answer 26

Used in research and diagnostic labs - immunofluorescence - resolution to 0.1 um

Question 27

Electron microscopy

Answer 27

Scanning and transmission - internal or surface detail available - resolution to 0.0003 um (0.3 nm)

Question 28

Preparation for staining

Answer 28

- drop of liquid containing bacteria is placed on a glass slide and allowed to dry - dried film is fixed onto slide using a chemical fixative or heat (passing slide thru a flame coagulates cell surface protein and sticks the bacteria to the slide) - stains are used that stain specific cell components (cytoplasm, flagella, cell wall, membranes, granules, nuclei, and spores)

Question 29

Positive stains

Answer 29

Have an affinity for one or more cell components - simplest stains are colored cationic salts (basic dyes) that combine with phosphate groups (negatively charged) of nucleic acids - ex: methylene blue

Question 30

Negative stains

Answer 30

Acidic dyes that do not penetrate cells - background contrasts with cells - ex: India ink

Question 31

Differential stains

Answer 31

Used to separate bacteria into groups based on their ability to take up and retain certain dyes - ex: Gram stain, acid fast stain

Question 32

Gram stain

Answer 32

Divides all eubacteria into 2 groups - primary stain: Gentain or crystal violet, all bacteria take it up - mordant: Gram's iodine and decreases crystal violet solubility - decolorizer: ethyl alcohol removes purple dye from some bacteria, but not others - counterstain: Safranin = bacteria that retain purple dye and resist decolorization are Gram positive, bacteria that were decolorized take up counterstain and are Gram negative

Question 33

What is Gram's stain used to determine?

Answer 33

- GR: gram's reaction - A: arrangement (spatial orientation resulting as a consequence of growth - M: morphology (form of cells)

Question 34

How to determine gram's reaction without staining

Answer 34

Add a bacterial colony to a drop of 10% KOH and stir - if solution is soapy, stringy, slimy, or viscous then bacteria are gram negative - reaction is caused by saponification of phospholipids in the outer membrane

Question 35

Unstained

Answer 35

Both gram-positive and gram-negative organisms are clear

Question 36

Crystal violet

Answer 36

Both gram-positive and gram-negative organisms are violet

Question 37

Iodine

Answer 37

Both gram-positive and gram-negative are violet

Question 38

Decolorization

Answer 38

- gram positive organisms are violet | - gram negative organisms are clear

Question 39

Safranin

Answer 39

- gram positive organisms are purple | - gram negative organisms are red