1. Microorganisms are classified through taxonomy, which involves identification, classification, and nomenclature of organisms. 2. Taxonomic classification categories arrange species in a hierarchical order from domain to genus. Identification techniques include microscopy, culture characteristics, biochemical tests, and nucleic acid analysis. 3. Bacteria can be classified by morphology, staining, culture characteristics, oxygen requirements, metabolism, and environmental tolerances. Cocci, bacilli, vibrios, spirochetes, and spirilla are morphological groups.

1. Classification of microorganisms, growth
properties and characteristics
Wewedru Izale, MSc (ID)
Microbiology Department, MNRH

2. Introduction
• The science of organizing, classifying and naming of organisms is called
taxonomy.
• The word comes from the Greek taxis, 'order', nomos, 'law' or 'science'.
• Taxonomy:
oIdentification - characterizing organisms
o Classification - arranging into similar groups
o Nomenclature - naming organisms
• Prokaryote classification involved techniques used to characterize and
identify prokaryotes e.g.. microscopic examination, cultural
characteristics, biochemical testing, nucleic acid analysis

3. Taxonomy
Taxonomic classification, categories are arranged in hierarchical order and
species is basic unit:
• Domain
• Kingdom
• Phylum (pl: Phyla) or Division
• Class
• Order
• Family
• Genus (pl: Genera )
• Species (pl: Species )

4. Taxonomy…
• Domain/Kingdom Bacteria
• Phylum Schizomycophyta
• Class Schizomycetes
• Order Enterobacteriales
• Family Enterobacteriaceae
• Genus Shigella
• Species dysenteriae

5. Taxonomy…
• Definition of “species” in microbiology;
o Type strains:
“Known” well-characterized pure cultures; references for the
identification of unknowns
o American Type Culture Collection (ATCC)

6. Taxonomy…
Species” vs. “Strain”
• Species: A specific or defined type of organism, defined by similarity
with known species.
• Strain: Genetic variation within a species.

7. Taxonomy…
• Nomenclature
oScientific name (Systematic Name)
Binomial System of Nomenclature
oGenus name + species name
italicized or underlined
genus name is capitalized and may be abbreviated
species name is never abbreviated.
e.g. Bacillus subtilis
B. subtilis

8. Taxonomy…
Nomenclature (cont.)
• Common or descriptive names
(trivial names)
eg: tubercle bacillus
(Mycobacterium tuberculosis)
meningococcus
(Neiserria meningitidis)
Group A streptococcus
(Streptococcus pyogenes )

9. Importance of taxonomy
1. Allows the organization of huge amounts of knowledge about the
organisms .
2. Allows for predictions & frame hypothesis for further research based on
knowledge of similar organisms.
3. Places microorganisms in meaningful and useful groups with precise
names .
4. Provides accurate identification of microorganisms (e.g. the need to
know the pathogen for a clinical test).
5. Microbial Evolution & Diversity.
6. Universal Phylogenetic Tree.

10. Classification Systems
1. Microscopic morphology ( morphology & staining reaction )
2. Macroscopic morphology – colony appearance
3. Physiological / biochemical characteristics
4. Chemical analysis
5. Serological analysis
6. Genetic and molecular analysis;
• G + C base composition
• DNA analysis using genetic probes
• Nucleic acid sequencing and rRNA analysis

11. Classification System…
7. Phage typing
8. Bacteriocine typing
9. Animal pathogenicity and Toxigenicity
10.Antimicrobial susceptibility testing.

12. Classification of Microorganisms:
•Microbes can be classified into four major groups:
Protozoa, fungi, viruses and bacteria.
1. Protozoa: These are unicellular organisms with protoplasm differentiated
into nucleus and cytoplasm.
Diameters in the range of 2-100 μm.
The most important groups of medical protozoa are:
a) Amoeba: Entamoeba species. Mode of Motility: pseudopodia.

13. b) Mastigophora: Mode of Motility: the Flagella.
• Gastrointestinal flagellates: Giardia intestinalis
• Urogenital flagellates: Trichomonas vaginalis
• Tissue and blood flagellates: Trypanosoma, Leishmania

14. Trypanosoma, and Leishmania .

15. c) Ciliophora: motile by cilia.
• Example: Balantidium coli.

16. d) Sporozoa: intracellular infection.
• Example: Plasmodium that cause Malaria.

17. 2- The Fungi
Fungi are saprophytic or parasitic organisms possessing relatively rigid cell walls.
Medical fungi:
1. Moulds: Branching filaments; hyphae, mycelium. Usually 2 to 10 μm in
width.
e.g. Epidermophyton, Trichophyton, Microsporum, Aspergillus.
2. True Yeasts: Ovoid or spherical cells that reproduce asexually by
budding or fission and sexually with formation of spores.
e.g. Cryptococcus spp.
3. Dimorphic fungi: Produce a vegetative mycelium at room temperature but are
yeast like in infected lesions/tissue
e.g.: Histoplasma.
4- Yeast- like fungi: e.g: Candida ( Pseudomycelium).

19. 3- The viruses:
Viruses consist of DNA or RNA enclosed in a simple protein shell known
as a capsid.
General properties of viruses:
• They are very small in size, from 10-400 nm.
• They contain one kind of nucleic acid (RNA or DNA) as their genome.
• They are metabolically inert
• They are obligate intracellular parasites.
• They are only seen by electron microscope.
• Depend on the parasitized cell for survival and multiplication

21. 4. The Bacteria
• Bacteria are classified and identified to distinguish one organism from
another ,and to group similar organisms by criteria of interest to
microbiologists or other scientists.
• Bacteria can be classified by:
1. colony shape in culture
2. motility
3. morphological characteristics other than shape e.g. multiple flagella
4. metabolic activity ( Biochemical reactions) eg. sugars they ferment
5. DNA sequence
6. Gram stain reactions

22. Classification of bacteria
Bacteria can be classified according to morphology and staining reaction into the following groups:
a) Higher bacteria :
•Filamentous bacteria: Streptomyces (antibiotic producers).
b)True bacteria/lower bacteria:
1.Cocci: Gram positive: Staphylococcus, Streptococcus.
Gram negative: Neisseria.
2. Bacilli: Gram positive: Bacillus, Clostridum, Corynebacterium.
Gram negative: Enterobacteriaceae, Brucella.
3. Spirochetes: Slender flexuous spiral bacteria. E.g. Borrelia, Treponema, Leptospira.
4. Mycoplasma: The Smallest bacteria that lack of a rigid cell wall.
5. Rickettsiae and Chlamydiae: intracellular parasites.

23. Morphological Classification:
Morphology and arrangement of bacterial cells are criteria used for
classification of bacteria into following groups:
1. Cocci (singular: coccus).
2. Rods (bacilli), (singular: rod, bacillus).
3. Vibrios (singular: vibrio).
4. Spirilla (singular :Spirillum)
5. Spirochaetes. (Singular: spirochaete).
1. Cocci:
Round or oval bacteria measuring about 0.5-1.0 µm in diameter. When
they are multiplying, cocci may form pairs, chains, or irregular groups.

24. • Cocci in pairs are called diplococci, e.g.meningococci
and gonococci.
• Cocci in chains are called streptococci, e.g. Streptococcus
pyogenes.
• Cocci in irregular groups are called Staphytococci, for
example, Staphylococcus aureus

25. 2. Rods (bacilli):
These are stick-like bacteria with rounded, square, or swollen
ends. They measure 1-10 µm in length by 0.3-1.0 µm in width.
It may arranged in:
A- Chains, for example, Streptobacillus species.
B- Branching chains, for example, lactobacilli .
C- Mass together, for example, Mycobacterium leprae.
D- Remain attached at various angles resembling Chinese letters,
for

26. 3-Vibrios:
These are small slightly curved rods measuring 3-4 µm in length by 0.5
µm in width.
Most vibrios are motile with a single flagellum at one end and show a
rapid darting motility.
E.g. Vibrio cholerae.

27. 4-Spirochetes:
These are flexible, coiled, motile organism, 6-20 µm in length.
They progress by rapid body movements.
• Spirochetes are divided into three main groups:
A- Treponemes. B- Borreliae. C- Leptospires

28. Cultural characteristics
• Bacteria show characteristic type of growth on solid media under
appropriate cultural conditions .
• Colony morphology can be used in presumptive identification.
• Colonies can be varying in size and diameter, in outline (circular, wavy,
rhizoid etc.) elevation (flat, raised, convex, etc.) and translucency
(transparent, opaque, and translucent).
• Colonial colour or the changes that they bring about in their
surroundings is also used as diagnostic tools in the tentative
identification of the bacteria e.g. β – and α – hemolytic colonies.

29. Aerobic and anaerobic conditions
• Bacteria are also classified based on the requirement of oxygen for their survival.
• Aerobes use oxygen for respiration.
• Anaerobes do not use oxygen for respiration.
• Microaerophiles require low oxygen concentration.
• Facultative anaerobes can survive in presence or absence of oxygen.
• Obligate aerobes cannot survive without oxygen.
• Obligate anaerobes cannot survive in presence of oxygen.

30. Autotrophs and Heterotrophs
• Autotrophic bacteria obtain carbon from CO2 or use sunlight.
• Heterotrophic bacteria obtain sugar from the environment (e.g.living
cells/organisms).

31. Classification based on environment/ecology
• Mesophiles - which require moderate conditions to survive.
• Neutrophiles - which require moderate conditions to survive.
• Extremophiles - which can survive in extreme conditions.
• Acidophiles - which can tolerate low pH conditions.
• Alkaliphiles - which can tolerate high pH conditions.

32. Classification based on environment/ecology…
• Thermophiles - which can resist high temperature.
• Psychrophilic bacteria - which can survive extremely cold conditions.
• Halophiles - which can survive in highly saline conditions.
• Osmophiles - which can survive in high sugar osmotic conditions.

33. The End!