Bacteria – Morphology & Classification

Bacteria – Morphology & Classification
? Microorganisms – several classes of living beings
? Based on the organization of their cellular structures, all living cells can be divided into two groups: eukaryotic and prokaryotic
? Eukaryoticcell types - Animals, plants, fungi, protozoans, and algae
? Prokaryotic cell types - bacteria & blue green algae


Schematic of typical animal (eukaryotic) cell, showing subcellular components.
Organelles: (1) nucleolus (2) nucleus (3) ribosome (4) vesicle
(5) rough endoplasmic reticulum (ER) (6) Golgi apparatus (7) Cytoskeleton
(8) Smooth ER (9) mitochondria (10) vacuole (11) cytoplasm (12) lysosome (13) centrioles

Prokaryotic Cells
? much smaller (microns) and more simple than eukaryotes
? Prokaryotes are molecules surrounded by a membrane and cell wall.
? They lack a true nucleus and don’t have membrane bound organelles like mitochondria, etc.
? large surface-to-volume ratio : nutrients can easily and rapidly reach any part of the cells interior
Size of Bacteria
? Unit of measurement in bacteriology is the micron (micrometer, µm)
? Bacteria of medical importance
0.2 – 1.5 µm in diameter, 3 – 5 µm in length
Shape of Bacteria
? Cocci – spherical/ oval shaped major groups
? Bacilli – rod shaped
? Vibrios – comma shaped
? Spirilla – rigid spiral forms
? Spirochetes – flexible spiral forms
? Actinomycetes – branching filamentous bacteria
? Mycoplasmas – lack cell wall

Arrangement of bacteria:
Cocci :Coccus
Cocci in pair – Diplococcus
Tetrad – groups of four

Cocci in chain - Streptococci



Cocci in cluster - Staphylococci
Sarcina – groups of eight
Arrangement of bacteria: Bacilli




Other shapes of bacteria

Comma shaped Spirilla



Spirochetes
Anatomy of a Bacterial Cell


Bacterial Taxonomy
? Taxonomy is the science of classification
? Includes three components:
1. Classification:arrangement of organisms into taxonomic groups on the basis of similarities.
2. Identification: distinguish desirable organisms from undesirable ones & to isolate & identify the causative agent of a disease.
3. Nomenclature: naming an organism by international rules according to its characteristics.
Classification Systems in the Prokaryote:
1. Microscopic morphology
2. Macroscopic morphology – colony appearance
3. Physiological / biochemical characteristics
4. Chemical analysis
5. Serological analysis ex.Slide Agglutination Test
6. Genetic and molecular analysis
• G + C base composition
• DNA analysis using genetic probes
• Nucleic acid sequencing and rRNA analysis
Bacterial Taxonomy Based on Bergey’s Manual
? Bergey’s Manual of Determinative Bacteriology – five volume resource covering all known prokaryotes
? Orderly arrangement :
Domain- Kingdom – Division – Class – Order – Family – Tribe – Genus – Species
? Phylogenetic classification – represents a branching tree like arrangement. One characteristic being used for division at each branch or level
? Molecular or Genetic classification – based on the degree of genetic relatedness of different organisms
? Intraspecies classification – based on biochemical properties (biotypes), antigenic features (serotypes), bacteriophage susceptibility (phage types)
2 Types of Prokaryotic Cell
? Eubacteria
? Archaebacteria which live in extreme environments
Ex. Thermoacidophiles, Extremehalophiles, Methanogens

Eubacteria
1.gram-negative that have cell wall:
? Cell envelope (outer membrane, an inner, peptidoglycan) & cytoplasmic membrane.
? Cell shape :spherical, oval, straight or curved rods, helical, or filamentous
? Some encapsulated
? Reproduce by Binary fission
? Motility by flagella or gliding
? Phototrophic or nonphototrophic
? Aerobic, anaerobic, facultatively anaerobic & microaerophilic
? Some obligate intracellular parasites
2. gram-positive that have cell walls
? Cell wall
? Cells :spherical, rods or filaments, may be nonbranching
? Binary fission
? Some produce spores
? Chemosynthetic heterotrophs
? Aerobic,anaerobic & facultatively anaerobic
3. Eubacteria lacking cell walls
? Called mycoplasma
? Enclosed by plasma membrane
? Resemble L-forms

Species of bacteria - “population of cells with similar characteristics”
Strain of bacteria - “group of cells derived from a single cell”
Typesubspecies that can show differences in antigenic makeup (serotype or serovar), susceptibility to bacterial viruses (phage type) and in pathogenicity (pathotype)
Subtyping:Distinguish between strains of a given species or to identify a particular strain in epidemic circumstances.Ex. Vibrio cholera
More 130 serogroups (O polysaccharide of Lps )
? Molecular typing methods: LPS- based methods (analysis of LPS by SDS-PAGE method), protein based methods & nucleic acid –based methods(PCR amplification & restriction endonuclease digestion.
? Detecting the reactivity of monoclonal Abs with epitopes on LPS.

? Two kinds of name are given to bacteria
? Casual / common name – for local use, varies from country to country e.g. “typhoid bacillus”
? Scientific / International Name – same all over world, consists of two words (in Italics)
Binomial system uses 2 names
Genus species
ex. Bacillus subtilis
ex. Staphylococcus aureus