1.3 Microbial classification & taxonomy, bacterial structure Flashcards
explain the concept of microbial phylogeny
•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)
what is molecular phylogeny?
the tool that enables us to understand the complexity of life and the relationships between living forms
list the characteristics of a prokaryotic cell
- nucleoid
- no nuclear membrane
- haploid chromosome
- no mitotic division (replicate by binary fission)
- no mitochondria
- no Golgi apparatus, microtubules
- 70S ribosomes
- motile by flagella
list the characteristics of a eukaryotic cell
- nucleus
- nuclear membrane present
- diploid chromosome
- mitotic division present
- mitochondria present
- 80S ribosomes
- more complex
provide a simple classification of viruses
- Smallest: size measured in nanometers (nm)
- Visualized using EM
- Obligate intracellular microbes
- Either DNA or RNA
- Enveloped or not enveloped
provide a simple classification of bacteria
- Larger: size measured in micrometers (μm)
- Visualized with light microscope
- Some are intracellular pathogens
- Both DNA & RNA
- Encapsulated or un-encapsulated
provide a simple classification of fungi
- Yeasts e.g. Candida spp.
- ‘Dimorphic’ fungi: moulds at lower ambient temperatures; yeasts at higher temperatures e.g. Histoplasma spp.
- Moulds e.g. Aspergillus spp
provide a simple classification of parasites
- Protozoa: e.g. Plasmodium spp., amoeba, etc.
- Trematodes -’flukes’ e.g. Schistosoma spp.
- Cestodes–flatworms (e.g. Taeniaspp. –tapeworms)
- Nematodes –roundworms (e.g. Ascaris lumbricoides)
discuss the manners in which bacteria can be classified based on morphology
- bacterial staining
- size
- shape
- arrangement
what types of bacterial staining reactions are there?
- gram staining
2. Acid-fast
describe the results of gram staining reactions
- Gram-positive (dark-blue/purple)
2. Gram-negative (pink)
describe the results of Acid-fast staining reactions
- stains poorly with Gram stain e.g. Mycobacterium tuberculosis
- Ziehl-Neelsen stain; Kinyoun stain
in what unit is bacterial morphology measured in?
in microns
describe the different bacterial shapes possible
- Cocci
- Bacilli
- Spiral
- Bacilli can be cocco-bacillary, pleomorphic or club shaped
- Spiral shape can be tight or loose coils
describe the different bacterial arrangements possible
e. g. cocci in chains
e. g. cocci in clusters
name an alternative manner of bacterial classification
- 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
Capsule (mostly polysaccharide):
antiphagocytic; antigenic/ immunogenic
Flagella (proteinaceous):
locomotion; antigenic; ? immune evasion
Fimbriae/pili
adherence
Cell wall (cytoskeleton = peptidoglycan):
rigidity & shape; protection against osmotic pressure -prevention of lysis; antigenic
Cytoplasmic membrane:
cell respiration; cell precursor synthesis
Spores:
protect species of genera Bacillus and Clostridium from unfavourable conditions
ULTRASTRUCTURAL FEATURES:
capsules, flagella, fimbriae/pili; bacterial spores
explain the differences in cell wall components between gram positive vs gram negative bacteria
need to complete from notes
draw a labelled diagram of a typical bacterial cell illustrating all the cellular components
(refer to notes)
list the order of bacterial nomenclature/ taxonomy
Phylum→Order→Family→Tribe→Genus→Species
