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Microbiology Lec
1
...
g
...
the amino acid protein sequence is the same as for some normal cellular proteins (Pr-like)
but they are folded differently
•A fter entry into human cells they modify the folding of normal protein (Pr-like) and turn them
in prions,

BACTERIAL STRUCTURE

eukaryote

prokaryote

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Characteristic

Procaryote

Eukaryote
Algae, Fungi, Plants,
Protozoans, Animals

Size

0,5-5μm

>5μm

Cell wall

Peptidoglycans, proteins,
lipids (except for
mycoplasmas)

Absent (present for fungi)

Cytoplasmic membrane

Does not contain sterols

Contain sterols

Nuclear structure

No nuclear membrane

Nuclear membrane

Genetic organization

Single circular DNA
molecule
Exons, no introns
No DNA- associated
histones
mRNA - mono and
polycistronic

Linear DNA, more than one
chromosome
Exons and introns
Histones associated with
DNA
mRNA- monocystronic

Cell division

Binary fission (asexual)

Mitosis or meiosis (sexual
and asexual)

Cytoplasmic structure
Mitochondria
Endoplasmic reticulum
Golgi bodies
Ribosomes

Absent
Absent
Absent
70S* (30S+ 50S)

Present
Present
Present
80S (40S+60S)

Respiration

Via cytoplasmic membrane

Via mitochondria

Distinguishing characteristics of procaryotes and eukaryotes

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Bacterial classification :
BACTERIA
•most pathogenic bacteria are capable of independent growth
• may be cultured on artificial media
•some bacteria lack the ability to produce important metabolites
•-must be provided exogenously (culture media , neighboring bacteria, infected cells)

•Commensal organisms colonize body surfaces
•without doing harm
•are referred to as normal microbial flora (e
...
Escherichia coli)

•Pathogens damage the human host
•by direct invasion and injury (e
...
Shigella species)
• by the production of harmful toxic products (e
...
Clostridium species)

•Opportunistic organisms
•in normal individuals are harmless,
•cause severe disease in imunocompromise patients /if they penetrate a territory from which
they are ussualy excluded( e
...
as a result of trauma or surgery

•Zoonotic organisms
• cause disease in vertebrates other than humans
•may be acquired through contact with infected animals or animal products
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Bacterial ultrastructure:

Essential components : (Cel wall \Cytoplasmic membrane\Cytoplasma \Nucleoid\ Ribosoms )
Optional components: (Capsule\ Flagella\ Pilli\ Endospors )

CELL ENVELOPE:
•Components- cell wall and underlyng cytoplasmic membrane

A
...
g
...

•it consists of a relatively thin peptidoglycan sheet between the plasma membrane and a
phospholipid-lipopolysaccharide outer membrane
• the periplasm- the space between the inner (plasma) and outer membranes (wherein the
peptidoglycan resides)
•the cell wall are not completely destroyed by lysozyme-resultant structure: spheroplast

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GRAM POSITIVE BACTERIA :have a simpler but thicker cell wall consisting of multiple layers of
peptidoglycan with teichoic acid polymers dispersed throughout
...
an addition
membrane , the outer membrane (OM) , lies above the peptidoglycan layer

B - CYTOPLASMIC MEMBRANE:
structurally similar to the cell membranes of eukaryotes do not contain sterols
•40 percent phospholipid, 60 percent protein
...


Functions of the procaryotic plasma membrane
1
...
Location of transport systems for specific solutes (nutrients and ions)
3
...
Synthesis of membrane lipids (including lipopolysaccharide in Gram-negative cells)
5
...
Assembly and secretion of extracytoplasmic proteins
7
...
Chemotaxis (both motility per se and sensing functions)
9
...


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PLASMID DNA:
•circular
•much smaller than bacterial chromosomes
•found in some bacteria
•capable of self replication
•encode variable numbers of genes , are nonessential, but may be important :
•to pathogenicity (through production of bacterial toxins)
•to survival under special condition (in the presence of an antibiotic or chemical)

•2 types :
>fertility factors (episomes)- can integrate their DNA into the bacterial chromosome
> drug resistance factors – do not integrate

TRANSPOSONS
•small piece of DNA that move between the DNA of bacteriophage
•are not capable of self replication
•code for antibiotic resistance, enzymes, methabolic enzymes, toxins

Ribosomes
•are complex globular structures composed of several RNA molecules and many associated
proteins
•they function as the active centers for protein synthetis
...


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External structures
...

-A true capsule - a discrete detectable layer of polysaccharides deposited outside the cell wall
outlined by India ink viewed by light microscopy- Streptococcus pneumoniae
-A less disc rete structure or matrix which embeds the cells is a called a slime layer or a biofilmBacteroides

FLAGELLA:
•are present on many bacteria and are responsible for the motility
•consists of three parts, filament, hook and basal body- composed of different proteins
•are composed exclusively of flagellin and are driven by the rotary action of a swivel –like basal
hook

PILII
>are protein fibers that cover the entire surface of bacteria
•common pili - play a role in bacterial adherence to mucosal surfaces (ussualy an essential step
in colonization and infection of a host)
•sex pili that are specifically involved in bacterial conjugation

ENDOSPORES- resistant forme- Bacillus, Clostridium
•Endospores exhibit no signs of life, being described as cryptobiotic
•are highly resistant to environmental stresses such as: high temperature, irradiation, strong
acids, disinfectants
•are probably the most durable cell produced in nature
•they germinate and become vegetative cells when the environmental stress is relieved
•endospore formation is a mechanism of survival rather than a mechanism of reproduction
...


Property

Vegetative cells

Endospores

Surface coats

Typical Gram-positive
murein cell wall polymer

Thick spore coat, cortex,
and peptidoglycan core wall

Microscopic appearance

Nonrefractile

Refractile

Calcium dipicolinic acid

Absent

Present in core

Cytoplasmic water activity

High

Very low

Enzymatic activity

Present

Absent

Macromolecular synthesis

Present

Absent

Heat resistance

Low

High

Resistance to chemicals and
acids

Low

High

Radiation resistance

Low

High

Sensitivity to lysozyme

Sensitive

Resistant

Sensitivity to dyes and
staining

Sensitive

Resistant

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Bacterial classification
Phenotypic classification
-microscopic morphology shape: round (cocci), rod-like (bacilli), comma, spiral (relaxed, thightly
coiled), pleomorphic (many-shaped), branching filamentous growth, arrangement (clusters, chains,
pairs) and Gram stain (positive, negative)
-macroscopic morphology of colonies (shape, elevation, opacity, color) smooth, rough, mucoid
-biotyping (biochemical markers – e
...
the presence of specific proteases, lipases)
-serotyping (identification of bacteria antigens)
-antibiogram patterns (patterns of susceptibility to antibiotics)
-phage typing (susceptibility to bacteriophages)

Analytic classification (genus, species, subspecies level
-cell protein analysis (by mass spectroscopy)
-cell wall fatty-acid analysis (e
...
mycolic acid-species of mycobacteria

Genotyping classification
-by analysis of their genetic material (guanidine + cytosine ration)
- nucleic acid sequence analysis

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