Escherichia coli (E. coli) is a bacterium that is commonly found in the gut of humans and warm-blooded animals.

1. Dr.Ga.BAKAVATHIAPPAN, M.Sc., M.Sc (Yoga)., M.Phil., B.Ed., PhD.,
Associate Professor, HOD of Zoology,
Saiva Bhanu Kshatriya College
Aruppukottai -626 101.
Virudhunagar District.
Tamilnadu
E. coli

2. • Escherichia coli
• also known as E. coli is a Gram-negative,
facultative anaerobic, rod-shaped, coliform
bacterium of the genus Escherichia that is
commonly found in the lower intestine of
warm-blooded organisms.
• Theodor Escherich, the German physician
who discovered Escherichia coli.
• Most E. coli strains are harmless, but some
serotypes (EPEC, ETEC etc) can cause
serious food poisoning in their hosts.
• The harmless strains are part of the normal
micro-biota of the gut, and can benefit their
hosts by producing vitamin K2.
• E. coli is expelled into the environment within
faecal matter. The bacterium grows
massively in fresh faecal matter under
aerobic conditions for 3 days, but its
numbers decline slowly afterwards.

10. Some of the differences between Fimbriae and Pili are as follows:
Characteristics
Fimbriae Pili
Definition Fimbriae are tiny bristle-like fibres
arising from the surface of
bacterial cells.
Pili are hair like microfibers that are
thick tubular structure made up of
pilin.
Length Thin and Shorter than pili, Less
rigid.
Thicker and Longer than fimbriae,
Rigid
Number No. of fimbriae are 200-400 per
cell.
No of pili are less 1-10 per cell.
Made up of Fimbrillin protein Pilin protein.
Found in Both gram positive and gram
negative bacteria.
Only gram negative bacteria.
Function Responsible for cell to surface
attachment. Specialized for
attachment i.e. enable the cell to
adhere the surfaces of other
bacteria.
Responsible for bacterial conjugation.
Two basic function of pili. They are
gene transfer and attachment.

12. Pili differ from
flagella in being shorter
and thinner, straight and
less ligid. But they are in
large number.
The sex pili make
contact between two
cells. Since they posses
hollow core, they act as
conjugation tube.
The tip of pilus
recognises the female
(F–) cell through which
the genetic material of
donor (F+) cell passes to
the recipient (female)
cell.

16. Plasmid
A plasmid is a small, circular piece of DNA that is different than the chromosomal DNA.
It replicates independently of chromosomal DNA. Plasmids are mainly found in bacteria
There are five main types of plasmids: fertility F-plasmids, resistance
plasmids, virulence plasmids, degradative plasmids, and Col plasmids.
Fertility plasmids, also known as F-plasmids,
contain transfer genes that allow genes to be transferred from one bacteria to
another through conjugation. Bacteria that have the F-plasmid are known as F
positive (F+), and bacteria without it are F negative (F–).
Resistance or R plasmids contain genes that help a bacterial cell defend
against environmental factors such as poisons or antibiotics. Some resistance
plasmids can transfer themselves through conjugation.
Virulence plasmids, which turn the bacterium into a pathogen. e.g. Ti
plasmid in Agrobacterium tumefaciens.
Degradative plasmids, which enable the digestion of unusual substances,
e.g. toluene and salicylic acid.
Col plasmids contain genes that make bacteriocins (also known as
colicins), which are proteins that kill other bacteria and thus defend the host
bacterium.

17. • Plasmids are used in genetic engineering to amplify,
or produce many copies of, certain genes.
• In molecular cloning, a plasmid is a type of vector.
• A vector is a DNA sequence that can transport
foreign genetic material from one cell to another cell,
where the genes can be further expressed and
replicated.
• Plasmids are useful in cloning short segments of
DNA.
• Also, plasmids can be used to replicate proteins, such
as the protein that codes for insulin, in large
amounts.

26. • Both gram positive and gram negative cell walls contain an
ingredient known as peptidoglycan (also known as murein).
• Peptidoglycan is a polysaccharide made of two glucose
derivatives, N-acetylglucosamine (NAG) and N-
acetylmuramic acid (NAM), alternated in long chains. The
chains are cross-linked to one another by a tetrapeptide that
extends off the NAM sugar unit, allowing a lattice-like
structure to form. The four amino acids that compose the
tetrapeptide are: L-alanine, D-glutamine, L-lysine or meso-
diaminopimelic acid (DPA), and D-alanine.

27. • The cell walls of gram negative bacteria are more complex
than that of gram positive bacteria, with more ingredients
overall. They do contain peptidoglycan as well, although
only a couple of layers, representing 5-10% of the total cell
wall. What is most notable about the gram negative cell
wall is the presence of a plasma membrane located outside
of the peptidoglycan layers, known as the outer membrane.
This makes up the bulk of the gram negative cell wall.
• It differs from the cell membrane by the presence of large
molecules known as lipopolysaccharide (LPS), which are
anchored into the outer membrane and project from the
cell into the environment. LPS is made up of three different
components: 1) the O-antigen or O-polysaccharide, which
represents the outermost part of the structure , 2) the core
polysaccharide, and 3) lipid A, which anchors the LPS into
the outer membrane. LPS is known to serve many different
functions for the cell.

28. • The cell walls of gram positive bacteria are composed
predominantly of peptidoglycan. In fact, peptidoglycan
can represent up to 90% of the cell wall, with layer
after layer forming around the cell membrane. The
NAM tetrapeptides are typically cross-linked with a
peptide interbridge and complete cross-linking is
common. All of this combines together to create an
incredibly strong cell wall.
• The additional component in a gram positive cell wall is
teichoic acid, a glycopolymer, which is embedded
within the peptidoglycan layers. Teichoic acid is
believed to play several important roles for the cell,
such as generation of the net negative charge of the
cell, which is essential for development of a proton
motive force.