Structure and classification of microbes
Structure and classification of microbes
Virus: Although they may seem to behave as living things,viruses are actually acellular, nonliving
particles. Viruses are not considered to be living organisms because they are incapable of carrying out all life
processes.
– Prokaryotes
have a relatively simple morphology and lack a true membrane-bound
nucleus
-----Bacteria
– Eukaryotes
are morphologically complex and have a true, membrane-bound nucleus
----- Fungi, Protozoa, algae
– Prokaryotes
• have a relatively simple morphology and lack a
true membrane-bound nucleus
-----Bacteria
– Eukaryotes
• are morphologically complex and have a true,
membrane-bound nucleus
----- Fungi, Protozoa, algae
Prokaryotic Cells
Nuclear region (nucleoid) is not
enveloped by a nuclear membrane.
Eukaryotic Cells
Nucleus is surrounded by a double membrane
layer.
Single chromosome present (circular)
More than one chromosome are present
(linear)
True nucleolus is absent.
Nucleolus is present.
An area inside the nucleus of a cell that is made up of RNA and proteins and is where ribosomes are made
Membrane bound organelles are absent.
Membrane bound organelles are
present.
Endoplasmic reticulum,
Golgi apparatus,
lysosomes,
Mitochondria
Prokaryotic Cells
Eukaryotic Cells
Cell size is 1-10μm
They are comparatively larger in size.
Cell size 10 - 100µm.
70 S ribosome (50+30)
80 S ribosome (60+40)
Multiplication of cell is by fission or
budding.
Cell division by mitosis or meiosis.
Cell Walls preset, which are chemically
complex.
Cell walls seen in only plant cells, which
are chemically simpler.
Cell type is usually unicellular.
Usually multicellular cells.
Example: Bacteria,
Example: Yeat, Protozoa, animal cells and
plant cells.
They are very minute in size
Size & Shape of bacteria
• The size of bacteria is measured in micrometer
(m) or micron ()
• 1 m=0.001mm = 10−6 m
• Most pathogenic bacteria measure from 0.1 to
10 .
Morphological Classification of Bacteria
Shape of Bacterial Cell
The three basic bacterial shapes are coccus
(spherical), bacillus (rod-shaped), and spiral
(twisted), however pleomorphic bacteria can
assume several shapes.
Cocci
• From kokkos meaning berry
• coccus for a single cell
Coccus
1. Diplococci- in pair
Streptococcus pneumoniae (pneumococci)
Neisseria gonorrhoeae (gonococci)
Neisseria meningitidis
(Meningococci )
Diplococcus
2. Streptococci- in chains
Streptococcus pyogenes
Streptococcus
3. Tetracocci- 4
Aerococcus, Pediococcus
Tetrad
4. Sarcine- 8,16,32..
Sarcina ventriculi
Sarcinae
5. Staphylococci- cluster
Staphylococcus aureus
Staphylococcus
• Diplococci—
Streptococcus pneumoniae
(pneumococci)
Neisseria gonorrhoeae
(gonococci)
Neisseria meningitidis
(Meningococci )
• Streptococci–
Streptococcus pyogenes
• Tetrads-Aerococcus, Pediococcus
• Sarcinae
Sarcina ventriculi
• Staphylococci
Staphylococcus aureus
Arrangement of Bacilli
• From baculus – meaning rod
Klebsiella pneumoniae
B.subtilis
corynebacterium diphtheriae
e. Coccobacilli
g. Vibrio
They are comma-shaped bacteria with less than one
complete turn or twist in the cell
Haemophilus influenzae
f. Trichomes:
Vibrio
cholerae
Vibrio
cholerae
saprospira grandis
The bacilli are arranged in chains with larger area of end-to-end contact between the cells.
Arrangement of Spiral Bacteria
• Spirilla
rigid spiral structure
Campylobacter jejuni,
Helicobacter pylori
• Spirochetes
flexible spiral structure
Leptospira interrogans,
Treponema pallidum
Others Shapes and Arrangements of Bacteria
• Filamentous bacteria – Actinomycetes
--Resemblance to radiating rays of sun
--Some of them form branching filaments resulting in a network
of filaments called ‘mycelium’.
Candidatus savagella
• Mycoplasmas
>---do not have cell wall & hence do not posses
fixed shape
Pleomorphic Bacteria
Mycoplasma pneumoniae, M. genitalium