classification of microorganisms Microbiology

Classification of Microorganisms

Taxonomy
• Organizing, classifying and
naming living things
• Formal system originated by
Carl von Linné (1701-1778)
• Identifying and classifying
organisms according to
specific criteria
• Each organism placed into a
classification system

Taxonomy
• Domain
• Kingdom
• Phylum
• Class
• Order
• Family
• Genus
• species

3 Domains
• Eubacteria
• true bacteria, peptidoglycan
• Archaea
• odd bacteria that live in extreme environments, high salt,
heat, etc. (usually called extremophiles)
• Eukarya
• have a nucleus & organelles (humans, animals, plants)

Taxonomy
• 5 main kingdoms:
• Protista
• Fungi
• Plantae
• Animalia
• Algae

Naming Micoorganisms
• Binomial (scientific) nomenclature
• Gives each microbe 2 names:
• Genus - noun, always capitalized
• species - adjective, lowercase
• Both italicized or underlined
• Staphylococcus aureus (S. aureus)
• Bacillus subtilis (B. subtilis)
• Escherichia coli (E. coli)

Evolution - living things change gradually
over millions of years
• Changes favoring survival are retained and less
beneficial changes are lost
• All new species originate from preexisting species
• Closely related organism have similar features
because they evolved from common ancestral forms
• Evolution usually progresses toward greater
complexity

Insert figure 1.15
Woese-Fox System

Classification Systems in the
Procaryotae

Classification Systems in the Procaryotae
1. Microscopic morphology
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

Bacterial Taxonomy Based on Bergey’s
Manual
• Bergey’s Manual of Determinative Bacteriology – five
volume resource covering all known procaryotes
• classification based on genetic information –phylogenetic
• two domains: Archaea and Bacteria
• five major subgroups with 25 different phyla

Major Taxonomic Groups of Bacteria
• Domain Archaea
• primitive, adapted to extreme habitats and modes of
nutrition
• Domain Bacteria
• Phylum Proteobacteria – Gram-negative cell walls
• Phylum Firmicutes – mainly Gram-positive with low G + C
content
• Phylum Actinobacteria – Gram-positive with high G + C
content

Diagnostic Scheme for Medical Use
• Uses phenotypic qualities in identification
• restricted to bacterial disease agents
• divides based on cell wall structure, shape,
arrangement, and physiological traits

Species and Subspecies
• Species
• collection of bacterial cells which share an overall similar pattern
of traits in contrast to other bacteria whose pattern differs
significantly
• Strain or variety
• culture derived from a single parent that differs in structure or
metabolism from other cultures of that species (biovars,
morphovars)
• Type
• subspecies that can show differences in antigenic makeup
(serotype or serovar), susceptibility to bacterial viruses (phage
type) and in pathogenicity (pathotype)

Archaea: The Other Procaryotes
• Constitute third Domain Archaea
• Seem more closely related to Domain Eukarya than to
bacteria
• Contain unique genetic sequences in their rRNA
• Have unique membrane lipids and cell wall construction
• Live in the most extreme habitats in nature, extremophiles
• Adapted to heat, salt, acid pH, pressure and atmosphere
• Includes: methane producers, hyperthermophiles, extreme
halophiles, and sulfur reducers

Eukaryotes
• Protista
• Fungi
• Plantae
• Animalia
• Algae

Fungal Classification
• Sexual reproduction
• Spores are formed following fusion of male and female
strains and formation of sexual structure
• Sexual spores and spore-forming structures are one
basis for classification
• Zygospores
• Ascospores
• Basidiospores

Fungal Classification
• Subkingdom Amastigomycota
• Terrestrial inhabitants including those of medical
importance:
1. Zygomycota – zygospores; sporangiospores and some
conidia
2. Ascomycota – ascospores; conidia
3. Basidiomycota – basidiospores; conidia
4. Deuteromycota – majority are yeasts and molds; no
sexual spores known; conidia

Protozoan Classification
• Difficult because of diversity
• Simple grouping is based on method of motility,
reproduction, and life cycle
1. Mastigophora – primarily flagellar motility, some flagellar
and amoeboid; sexual reproduction; cyst and trophozoite
2. Sarcodina – primarily ameba; asexual by fission; most are
free-living
3. Ciliophora – cilia; trophozoites and cysts; most are free-
living, harmless
4. Apicomplexa – motility is absent except male gametes;
sexual and asexual reproduction; complex life cycle – all
parasitic

Classification of
Microorganisms

Taxonomy
• 4 main kingdoms:
• Protista
• Fungi
• Plantae
• Animalia
• Algae

Major Taxonomic Groups of Bacteria
• Vol 1A: Domain Archaea
• primitive, adapted to extreme habitats and modes of
nutrition
• Vol 1B: Domain Bacteria
• Vol 2-5:
• Phylum Proteobacteria – Gram-negative cell walls
• Phylum Firmicutes – mainly Gram-positive with low G + C
content
• Phylum Actinobacteria – Gram-positive with high G + C
content

Classification of Microorganisms:
Microbes can be classified into four major groups:
1- Protozoa 2- Bacteria.
3- Fungi. 4- Viruses.
1- The 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.

a
B- Mastigophora: Mode of Motility: the Flagella.
Gastrointestinal flagellates: Giardia intestinalis
Urogenital flagellates: Trichomonas vaginalis
Tissue and blood flagellates: Trypanosoma, Leishmania .

Trypanosoma, and Leishmania .
a

C- Ciliophora: motile by cilia.
Example: Balantidium coli.

D- Sporozoa: intracellular infection.
Example: Plasmodium that cause Malaria.

2- The bacteria:
Bacteria are unicellular prokaryotic microorganisms that multiply by
binary fission.
Bacteria can be classified according to morphology, arrangement, and
staining reaction into the following groups:
1- Filamentous bacteria: Streptomyces: antibiotic producers.
2- True bacteria:
Cocci: Gram positive: Staphylococcus, Streptococcus.
Gram negative: Neisseria.
Bacilli: Gram positive: Bacillus, Clostridum, Corynebacterium.
Gram negative: Enterobacteriaceae, Brucella.
3- Spirochetes: Slender flexuous spiral bacteria.
Borrelia, Treponema, Leptospira.
4- Mycoplasma: The Smallest bacteria that lack of a rigid cell wall.
5- Rickettsiae and Chlamydiae: intracellular parasites.

3- The Fungi:
These are saprophytic or parasitic organisms possessing relatively rigid cell
walls.
Medical fungi can be divided into:
1- Mould: Branching filaments; hyphae, mycelium. Usually 2 to 10 μm in width.
Example: Epidermophyton, Trichophyton,
Microsporum, Aspergillus.
2- True Yeasts: these are ovoid or spherical cells that reproduce asexually by
budding and sexually with formation of spores.
Example : Cryptococcus spp.
3- Dimorphic fungi:
Produce a vegetative mycelium in artificial
media, but are yeast like in infected lesions.
Example: Histoplasma.
4- Yeast- like fungi: Example: Candida ( Pseudomycelium).

4- 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 20-300 m.
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

Structure of bacterial cells:
Size, Shape, and Arrangement of bacterial cells:
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. Spirochetes. (Singular: Spirochaete).
1. Cocci:
These are round or oval bacteria measuring about 0.5-1.0 micrometer in
diameter. When they multiplying, cocci may form pairs, chains, or
irregular groups.

a
Cocci in pairs are called diplococci, for example, meningococci
and gonococci.
Cocci in chains are called streptococci, for example Streptococcus pyogens.
Cocci in irregular groups are called Staphytococci, for example, Staphylococcus aureus.

2. Rods (bacilli):
These are stick-like bacteria with rounded, square, or swollen ends. They
measure 1-10 micrometer in length by 0.3-1.0 micrometer 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
example, Corynebacterium diphtheria.

3-Vibrios:
These are small slightly curved rods measuring 3-4 micrometer
in length by 0.5 micrometers in width.
Most vibrios are motile with a single flagellum at one end.
They show a rapid darting motility.
For example:
vibrio cholerae.

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

classification of microorganisms Microbiology

classification of microorganisms Microbiology

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classification of microorganisms Microbiology