Bacteriology
INTRODUCTION
The
Bacteria are a group of single-cell microorganisms with prokaryotic cellular
configuration.
bacteria
are the smallest organisms capable of independent existence.
The
genetic material (DNA) of prokaryotic cells exists unbound in the cytoplasm of
the bacterial cells with No nucleus, No organelles (mitochondria, chloroplast,
Golgi, etc.)
Bacteria
- l
The diameter of the
smallest body that can be resolved with naked eye is about 100um
- l The size of bacteria range from 0.1 to 10 μm (1 μm = 10−6 m)
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Average bacteria
0.5 - 2.0 um in diam.
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Surface Area ~12
um^2
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Volume is ~4 um
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Food enters through
SA, quickly reaches all parts of bacteria
- l Morphology of the bacterial cell
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Bacteria are
classified by direct examination with the light microscope through its
morphology and aggregation
Morphology of the bacterial cell
The basic forms are
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spheres (coccus)
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round-ended
cylinders (bacilli)
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vibrio (coma shaped
or curved )
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filamentous (long
filaments)
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spirochete (many
coils)
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Bacteria Have One of Three Cellular Shapes
 |
Rods (bacilli) |
 |
| Coccoid-Shaped |
 |
| Spirilla |
Cocci
Aggregations of Cocci
l pairs, or diplococci
(Neisseria)
l groups of four or eight known as tetrads (Micrococci)
l bead-like chains, or streptococci
(Streptococcus)
l grapelike clusters, or staphylococci
(Staphylococcu)
Arrangement of bacteria: Cocci
 |
| Coccus |
 | |
| Cocci in pair – Diplococcus |
 | |
| Tetrad – groups of four |
 | |
| Cocci in chain - Streptococci |
 | |
| Cocci in cluster - Staphylococci |
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Arrangement of bacteria: Bacilli
Other shapes of bacteria
Prokaryotic Cell
 | |
| Prokaryotic Cell |
Cytoplasm
l
80% Water {20%
Salts-Proteins)
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Ribosomes
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Inclusion bodies,
glycogen or starch
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DNA is circular,
Haploid
–
More efficient;
grows quicker
–
Mutations allow
adaptation to environment quicker
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Plasmids; extra
circular DNA
–
Antibiotic
Resistance
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No organelles
(Mitochondria, Golgi, etc.)
Structural components of Bacteria
A-Essential structural components
B-Non essential structural components
A-Essential structural components
l cell wall
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Cell membrane
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a nucleoid (DNA)
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Ribosomes
1-Cell wall
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found in all bacteria ,except mycoplasma .
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Peptidoglycans.
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Peptidoglycans
constitute almost 95% of the cell wall in some Gram positive bacteria and as
little as 5-10% of the cell wall in Gram negative bacteria
functions
of bacterial cell wall
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A. protect bacterial from osmotic pressure .
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B. give the bacteria it is shape .
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C. division started from the cell wall
2-The bacterial cytoplasmic membrane
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is a typical phospholipid bilayer and protein .
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Permeability barrier; transport of solutes; energy
generation; location of numerous enzyme systems
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3-The Nucleoid
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The nucleoid is a region of the cytoplasm which contains
the genome and a collection of related proteins.
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The bacterial genome resides on a single chromosome.
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Circular chromosome of supercoiled double-stranded DNA
negatively charged.
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Responsible of transfer of cellular information .
l
4-Bacterial Ribosomes
l
have a sedimentation coefficient of 70S and are composed of
30S and 50S subunits .
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for protein biosynthesis.
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B_Non essential structural components
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Capsule
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flagella .
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pili (or fimbriae)
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Plasmid
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Endospores
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mesosome
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Capsule
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is a well-defined structure of polysaccharide some are
simple (though unusual) polypeptides surrounding a bacterial cell and is
external to the cell wall.
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protects the
bacteria from phagocytosis and plays a role in bacterial adherence and
colonization .
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some times, it is
referred to as a slime layer.
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Flagella
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are protein called flagellin, appendages for locomotion.
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Medical importance
of flagella are :
-
movement of bacteria (motility)
-Spreading
of infection e. g. urinary tract infection
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Pili (fimbriae)
} Pili are proteinaceous
hair-like projections
} They are composed of molecules of a protein
called pilin
} There are two general classes, common pili and
sex pili .
} Common pili(fimbriae) cover the surface of the
cell cases adhesions of bacteria to the human cells and responsible for the
ability of bacteria to colonize surfaces and cells.
} the F or sex pilus,
apparently stabilizes mating bacteria(male and female) during the process of
conjugation (transfer genetic material ).
} The sex pilus is
diagnostic of a male bacterium and is involved in exchange of genetic material
between some Gram-negative bacteria.
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Mesosomes
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are convoluted invaginations of the plasma membrane.
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function in DNA replication and cell division as well as
in secretion.
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are termed septal mesosomes if they occur at the septum
(cross-wall) or lateral mesosomes if they are nonseptal
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Plasmids
are
small, circular, nonchromosomal, double-stranded DNA molecules.
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are capable of self-replication.
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are most frequently extrachromosomal, but may become
integrated into bacterial DNA.
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contain genes that confer protective properties, such as
antibiotic resistance, virulence factors, or their own transmissibility to
other bacteria.
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Endospores
} are formed as a
survival response to certain adverse nutritional conditions, such as depletion
of a certain resource.
} are metabolically
inactive bacterial cells that are highly resistant to desiccation, heat, and
various chemicals.
} germinate under
favorable nutritional conditions after an activation process that involves
damage to the spore coat.
} are helpful in
identifying some species of bacteria (e.g., Bacillus and Clostridium).
} are not reproductive
structures.
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Endospore
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