1.3 Microbial classification & taxonomy, bacterial structure

Question 1

explain the concept of microbial phylogeny

Answer 1

•Cyanobacteria is the first unicellular form of life identified ≈ 3.6 billion years ago.
•Molecular Phylogeny is the tool that enables us to understand the complexity of life and the relationships between living forms.
•This is done by comparing the ribosomal RNA ( rRNA) genes.
•rRNA is well conserved so helps identify relationships between organisms. In prokaryotes, get 16SrRNA & in eukaryotes , get 18SrRNA.
•Based on rRNA analysis, life has evolved into 3 main lineages:
1. Prokaryotes ( unicellular; bacteria)
2. Archae( unicellular microbes, not of clinical significance) &
3. Eukaryotes ( multicellular, more complex organisms like fungi, protozoa)

Question 2

what is molecular phylogeny?

Answer 2

the tool that enables us to understand the complexity of life and the relationships between living forms

Question 3

list the characteristics of a prokaryotic cell

Answer 3

1. nucleoid
2. no nuclear membrane
3. haploid chromosome
4. no mitotic division (replicate by binary fission)
5. no mitochondria
6. no Golgi apparatus, microtubules
7. 70S ribosomes
8. motile by flagella

Question 4

list the characteristics of a eukaryotic cell

Answer 4

1. nucleus
2. nuclear membrane present
3. diploid chromosome
4. mitotic division present
5. mitochondria present
6. 80S ribosomes
7. more complex

Question 5

provide a simple classification of viruses

Answer 5

1. Smallest: size measured in nanometers (nm)
2. Visualized using EM
3. Obligate intracellular microbes
4. Either DNA or RNA
5. Enveloped or not enveloped

Question 6

provide a simple classification of bacteria

Answer 6

1. Larger: size measured in micrometers (μm)
2. Visualized with light microscope
3. Some are intracellular pathogens
4. Both DNA & RNA
5. Encapsulated or un-encapsulated

Question 7

provide a simple classification of fungi

Answer 7

1. Yeasts e.g. Candida spp.
2. ‘Dimorphic’ fungi: moulds at lower ambient temperatures; yeasts at higher temperatures e.g. Histoplasma spp.
3. Moulds e.g. Aspergillus spp

Question 8

provide a simple classification of parasites

Answer 8

1. Protozoa: e.g. Plasmodium spp., amoeba, etc.
2. Trematodes -’flukes’ e.g. Schistosoma spp.
3. Cestodes–flatworms (e.g. Taeniaspp. –tapeworms)
4. Nematodes –roundworms (e.g. Ascaris lumbricoides)

Question 9

discuss the manners in which bacteria can be classified based on morphology

Answer 9

1. bacterial staining
2. size
3. shape
4. arrangement

Question 10

what types of bacterial staining reactions are there?

Answer 10

1. gram staining

2. Acid-fast

Question 11

describe the results of gram staining reactions

Answer 11

1. Gram-positive (dark-blue/purple)

2. Gram-negative (pink)

Question 12

describe the results of Acid-fast staining reactions

Answer 12

• stains poorly with Gram stain e.g. Mycobacterium tuberculosis
• Ziehl-Neelsen stain; Kinyoun stain

Question 13

in what unit is bacterial morphology measured in?

Answer 13

in microns

Question 14

describe the different bacterial shapes possible

Answer 14

1. Cocci
2. Bacilli
3. Spiral
   - Bacilli can be cocco-bacillary, pleomorphic or club shaped
   - Spiral shape can be tight or loose coils

Question 15

describe the different bacterial arrangements possible

Answer 15

e. g. cocci in chains

e. g. cocci in clusters

Question 16

name an alternative manner of bacterial classification

Answer 16

• culturable or non-culturable
  1. unculturable: bacteria that cannot be grown on any artificial non-living conditions
  2. growth requirements: aero-tolerance, fast vs slow growers

Question 17

Capsule (mostly polysaccharide):

Answer 17

antiphagocytic; antigenic/ immunogenic

Question 18

Flagella (proteinaceous):

Answer 18

locomotion; antigenic; ? immune evasion

Question 19

Fimbriae/pili

Answer 19

adherence

Question 20

Cell wall (cytoskeleton = peptidoglycan):

Answer 20

rigidity & shape; protection against osmotic pressure -prevention of lysis; antigenic

Question 21

Cytoplasmic membrane:

Answer 21

cell respiration; cell precursor synthesis

Question 22

Spores:

Answer 22

protect species of genera Bacillus and Clostridium from unfavourable conditions

Question 23

ULTRASTRUCTURAL FEATURES:

Answer 23

capsules, flagella, fimbriae/pili; bacterial spores

Question 24

explain the differences in cell wall components between gram positive vs gram negative bacteria

Answer 24

need to complete from notes

Question 25

draw a labelled diagram of a typical bacterial cell illustrating all the cellular components

Answer 25

(refer to notes)

Question 26

list the order of bacterial nomenclature/ taxonomy

Answer 26

Phylum→Order→Family→Tribe→Genus→Species