ENDO AND EXOTOXIN

1. Pt. Ravishankar Shukla
University
S.o.s in Biotechnology
Topic :- Types of Toxins
Guided By :-
Dr. K K Shukla
Submitted By :- P. Sujata
Msc I sem

2.  Pathogens
 Pathogenicity and Virulence
 Infection
 Virulence
 Adherence
 Damage of host cell
 Bacterial toxins
 Types of toxins
 Exotoxins
o Cytolytic toxin
o AB toxin
o Superantigen toxin
 Endotoxins
 Natural Host Resistance

3.  A host is an organism that harbors a
pathogen, another organism that lives on or
in the host and causes disease.
 The outcome of a host–pathogen relationship
depends on pathogenicity, the ability of a
pathogen to inflict damage on the host.
 Pathogenicity differs considerably among
potential pathogens, as does the resistance
or susceptibility of the host to the pathogen.
 An opportunistic pathogen causes disease
only in the absence of normal host
resistance.

4. PATHOGENICITY AND VIRULENCE
 Pathogenicity varies markedly for individual
pathogens.
 The quantitative measure of pathogenicity is called
virulence, the relative ability of a pathogen to cause
disease.
 Virulence can be expressed quantitatively as the
cell number that elicits disease in a host within a
given time period.
 The host–pathogen interaction is a dynamic
relationship between the two organisms, influenced
by changing conditions in the pathogen, the host,
and the environment.

5. Infection
 Infection refers to any situation in which
a microorganism is established and
growing in a host, whether or not the
host is harmed.
 Disease is damage or injury to the host
that impairs host function.
 Infection is not synonymous with
disease because growth of a
microorganism on a host does not
always cause host damage.
 Thus, species of the normal microflora
have infected the host, but seldom cause

6. Virulence
 Virulence is a pathogen's or microbe's ability to infect
or damage a host.
 virulence refers to the degree of damage caused by a
microbe to its host.
 The various traits or factors that allow
microorganisms to cause disease.
 These include:
Adhesion organelles
Toxin production
Evasion of host immune response
Resistance to antibiotics
Ability to invade host tissues

7.  A pathogen must usually gain access to host tissues
and multiply to cause disease.
 In most cases, this requires that the organisms
penetrate the skin or mucous membranes, surfaces
that are normally microbial barriers.
 Most microbial infections begin at breaks or wounds
in the skin or on the mucous membranes of the
respiratory, digestive, or genitourinary tract.
 Bacteria or viruses able to initiate infection often
adhere to epithelial cells through specific interactions
between molecules on the pathogen and molecules
on the host cell In addition, pathogens often adhere
to each other, forming biofilms.

8.  Most pathogens selectively adhere to particular
types of cells localized in a particular region of the
body.
 For example, Neisseria gonorrhoeae, the
pathogen that causes the sexually transmitted
disease gonorrhea, adheres to mucosal epithelial
cells in the genitourinary tract, eye, rectum, and
throat.
 Streptococcus pyogenes utilizes two cell-wall-
associated molecules, the M protein and
lipoteichoic acid, to form microfibrils that facilitate
attachment to host cells M protein is also
responsible for resistance to phagocytosis by
neutrophils, cells important in antibacterial
resistance.

9.  Influenza virus occurs in nature as an avian
pathogen, targeting the lung mucosal cells.
 A polymer coat consisting of a dense, well-
defined polymer layer surrounding the cell is
called a capsule.
 Both slime layers and capsules are important
for adherence to other bacteria as well as to
host tissues.

10.  Fimbriae and pili are bacterial cell surface
protein structures that may function in the
attachment process.
 For instance, the pili of Neisseria gonorrhoeae
play a key role in attachment to the urogenital
epithelium, and fimbriated strains of
Escherichia coli are more frequent causes of
urinary tract infections than strains lacking
fimbriae.
 Flagella can also increase adherence to host
cells.

12. Microbial toxins are toxins produced by micro-
organisms, including bacteria and fungi.
Microbial toxins promote infection and
disease by directly damaging host tissues and
by disabling the immune system.

13. Types of toxins

14.  Exotoxins are toxic proteins released from the pathogen cell as it
grows.These toxins travel from a site of infection and cause
damage at distant sites.
 Exotoxins fall into three categories: the cytolytic toxins, the AB
toxins, and the superantigen toxins.
1.The cytolytic toxins work by degrading cytoplasmic membrane
integrity, causing lysis.
2.The AB toxins consist of two subunits, A and B.The B component
binds to a host cell surface receptor, facilitating the transfer of the
A subunit across the targeted cytoplasmic membrane, where it
damages the cell.
3.The superantigens work by stimulating large numbers of immune
cells, resulting in extensive inflammation and tissue damage.
 A subset of the exotoxins are the enterotoxins, exotoxins whose
activity affects the small intestine, generally causing secretion of
fluid into the intestinal lumen resulting in vomiting and diarrhea.

16. Cytolytic Toxins
 Cytolytic toxins are secreted, soluble, extracellular proteins
produced by a variety of pathogens.
 Cytolytic toxins damage the host cytoplasmic membrane, causing
cell lysis and death. Because the activity of these toxins is most
easily observed with assays involving the lysis of red blood cells
(erythrocytes), the toxins are often called hemolysins
 However, they also lyse cells other than erythrocytes.
 Some hemolysins attack the phospholipid of the host cytoplasmic
membrane. Because the phospholipid lecithin (phosphatidylcholine)
is often used as a substrate, these enzymes are called lecithinases
or phospholipases.
 An example is the α-toxin of Clostridium perfringens, a lecithinase
that dissolves membrane lipids, resulting in cell lysis Because the
cytoplasmic membranes of all organisms contain phospholipids,
phospholipases sometimes destroy bacterial as well as animal
cytoplasmic membranes.

17. Cytolytic Toxin :-Example
 Staphylococcal α-toxin kills nucleated cells
and lyses erythrocytes.
 Toxin subunits first bind to the phospholipid
bilayer.
 The subunits then oligomerize into nonlytic
heptamers, now associated with the
membrane.
 Following oligomerization, each heptamer
undergoes conformational changes to
produce a membrane-spanning pore,
releasing the cell contents and allowing influx
of extracellular material, disrupting cell
function and causing cell death.

19. AB TOXINS
 AB Toxins Several pathogens produce AB exotoxins that inhibit protein
synthesis. The diphtheria toxin produced by Corynebacterium diphtheriae is an
AB toxin and an important virulence factor.
 Rats and mice are relatively resistant to diphtheria toxin, but human, rabbit,
guinea pig, and bird cells are very susceptible, with only a single toxin molecule
required to kill each cell.
 Diphtheria toxin is secreted by C. diphtheriae as a single polypeptide. Fragment
B specifically binds to a host cell receptor present on many eukaryotic cells, the
heparin-binding epidermal growth factor .
 After binding, proteolytic cleavage between fragment A and B allows entry of
fragment A into the host cytoplasm. Here fragment A disrupts protein synthesis
by blocking transfer of an amino acid from a tRNA to the growing polypeptide
chain
 The toxin specifically inactivates elongation factor 2 (EF-2), a protein involved in
growth of the polypeptide chain, by catalyzing the attachment of adenosine
diphosphate (ADP) ribose from NAD1. Following ADP-ribosylation, the activity of
the modified EF-2 decreases dramatically and protein synthesis stops.
 Diphtheria toxin is encoded by the toxgene in a lysogenic bacteriophage called
phage β. Toxigenic, pathogenic strains of C. diphtheriaeare infected with phage
βand encode the toxin. Nontoxigenic, nonpathogenic strains of C. diphtheriaecan
be converted to pathogenic strains by infection with phage β, a process called
phage conversion.

22.  Tetanus and Botulinum Toxins Clostridium tetani and Clostridium
botulinum are endospore forming bacteria commonly found in
soil.
 These organisms occasionally cause disease in animals through
potent AB exotoxins that are neurotoxins—they affect nervous
tissue.
 All pathogenic effects are due to neurotoxicity. C. botulinum
sometimes grows directly in the body, causing infant or wound
botulism, and also grows and produces toxin in improperly
preserved foods .
 Death from botulism is usually from respiratory failure due to
flaccid muscle paralysis.
 C. tetani grows in the body in deep wounds that become anoxic,
such as punctures.
 Although C. tetani does not invade the body from the initial site
of infection, the toxin can spread via the neural cells and cause
spastic paralysis, the hallmark of tetanus, often leading to death
.

23.  Botulinum toxins, the most potent biological toxins known, are
seven related AB toxins.
 One milligram of botulinum toxin is enough to kill more than 1
million guinea pigs.
 The major toxin is a protein that forms complexes with nontoxic
botulinum proteins to yield a bioactive protein complex.
 The complex then binds to presynaptic membranes on the
termini of the stimulatory motor neurons at the neuromuscular
junction, blocking the release of acetylcholine.
 Normal transmission of a nerve impulse to a muscle cell requires
acetylcholine interaction with a muscle receptor; botulinum
toxin prevents the poisoned muscle from receiving the excitatory
acetylcholine signal .
 This prevents muscle contraction and leads to flaccid paralysis
and death by suffocation, the outcome of botulism.

25. Tetanus toxin
 Tetanus toxin is also an AB protein neurotoxin.
 On contact with the central nervous system, this toxin is transported
through the motor neurons to the spinal cord, where it binds specifically to
ganglioside lipids at the termini of the inhibitory interneurons.
 The inhibitory interneurons normally work by releasing an inhibitory
neurotransmitter, typically the amino acid glycine, which binds to receptors
on the motor neurons.
 Glycine from the inhibitory interneurons then stops the release of
acetylcholine by the motor neurons and inhibits muscle contraction, allowing
relaxation of the muscle fibers.
 However, if tetanus toxin blocks glycine release, the motor neurons cannot
be inhibited, resulting in tetanus, continual release of acetylcholine, and
uncontrolled contraction of the poisoned muscles
 The outcome is a spastic, twitching paralysis, and affected muscles are
constantly contracted. If the muscles of the mouth are involved, the
prolonged contractions restrict the mouth’s movement, resulting in a
condition called lockjaw(trismus).
 If respiratory muscles are involved, prolonged contraction may result in
death due to asphyxiation.

27. Cholera Toxin- Enterotoxin
 Cholera toxin, an enterotoxin produced by V. cholerae, causes cholera .
 Cholera is characterized by massive fluid loss from the intestines, resulting in severe diarrhea, life
threatening dehydration, and electrolyte depletion .
 The disease starts by ingestion of V. cholerae in contaminated food or water. The organism
travels to the intestine, where it colonizes and secretes the cholera AB toxin.
 In the gut, the B subunit binds specifically to GM1 ganglioside, a complex glycolipid found in the
cytoplasmic membrane of intestinal epithelial cells.
 The B subunit targets the toxin specifically to the intestinal epithelium but has no role in alteration
of membrane permeability; the toxic action is a function of the A chain, which crosses the
cytoplasmic membrane and activates adenylate cyclase, the enzyme that converts ATP to cyclic
adenosine monophosphate (cAMP).
 The cAMP molecule is a cyclic nucleotide that mediates many different regulatory systems in cells,
including ion balance. The increased cAMP levels induced by the cholera enterotoxin induce
secretion of chloride and bicarbonate ions from the epithelial cells into the intestinal lumen.
 This change in ion concentrations leads to the secretion of large amounts of water into the
intestinal lumen. In acute cholera, the rate of water loss into the small intestine is greater than the
possible reabsorption of water by the large intestine, resulting in a large net fluid loss.
 Cholera treatment is by oral fluid replacement with solutions containing electrolytes and other
solutes to offset the dehydration coupled ion imbalance.
 Expression of cholera enterotoxin genes ctxA and ctxB is controlled by toxR. The toxR gene
product is a transmembrane protein that controls cholera A and B chain production as well as
other virulence factors, such as the outer membrane proteins and pili required for successful
attachment and colonization of V.cholerae in the small intestine.

29. superantigens
 Exotoxins called superantigens act by stimulating
as many as 30% of host T cells to over express
and release massive amounts of cytokines from
other host immune cells in the absence of a
specific antigen .
 The excessive concentration of cytokines causes
multiple host organs to fail, giving the pathogen
time to disseminate.
 By triggering this “cytokine storm,” superantigens
cause life-threatening disease; fever, fluid loss,
and low blood pressure result in shock and death.

31.  The lipopolysaccharide (LPS) in the outer membrane
of Gramnegative bacteria is toxic to humans.
 LPS is called an endotoxin because it is bound to
the bacterium and is released when the
microorganism lyses, although some may also be
released during cell division.
 The toxic component of LPS is the lipid portion,
called lipid A.
 Lipid A is not a single macromolecular structure;
rather, it is a complex array of lipid residues.
 Lipid A is heat stable and toxic in nano gram amounts
but only weakly immunogenic.
 Typical Gram negative cell walls include additional
layers besides peptidoglycan .

32.  The lipid A of various Gram-negative bacteria produces similar
systemic effects regardless of the microbe from which it is derived.
 These include fever (i.e., endotoxin is pyrogenic), shock, blood
coagulation, weakness, diarrhea, inflammation, intestinal
hemorrhage, and fibrinolysis (enzymatic breakdown of fibrin, the
major protein component of blood clots)
 The main biological effect of lipid A is an indirect one, mediated by
host molecules and systems, rather than by lipid A itself. For
example, endotoxins initially activate a protein called the Hageman
factor (blood clotting factor XII), which in turn results in unregulated
blood clotting within capillaries (disseminated intravascular
coagulation) and multi organ failure.
 Endotoxins also indirectly induce a fever in the host by causing
macrophages to release endogenous pyrogens that reset the
hypothalamic thermostat. One important endogenous pyrogen is the
cytokine interleukin-1 (IL-1). Other cytokines released by
macrophages such as the tumor necrosis factor, also produce fever.
 The net effect is often called septic shock and can also be induced
by certain pathogenic fungi and Gram-positive bacteria.

35. NATURAL HOST RESISTANCE
Physical and Chemical Barriers
 The structural integrity of tissue surfaces poses a barrier to penetration by
microorganisms. In the skin and mucosal tissues, potential pathogens must first
adhere to tissue surfaces and then grow at these sites before traveling
elsewhere in the body.
 Resistance to colonization and invasion is due to the production of host defense
substances and to various anatomical mechanisms.
 The skin is an effective barrier to the penetration of microorganisms. Sebaceous
glands in the skin secrete fatty acids and lactic acid, lowering the acidity of the
skin to pH 5 and inhibiting colonization of many pathogenic bacteria (blood and
internal organs are about pH 7.4).
 Microorganisms inhaled through the nose or mouth are removed by ciliated
epithelial cells on the mucosal surfaces of the nasopharynx and trachea.
 Potential pathogens ingested in food or water must survive the strong acidity in
the stomach (pH 2) and then must compete with the abundant resident
microflora present in the small and large intestines.
 Finally, the lumen of the kidney, the eye, the respiratory system, and the cervical
mucosa are constantly bathed with secretions such as tears and mucus
containing lysozyme, an enzyme that can digest the cell wall and kill bacteria

36. Reference
 Brock -Biology of Microorganisms 13th Edition
 Prescott’s - Microbiology 10th Edition

37. Thank you