aeromonas speecies

1. Pathogenecity and
virulence factor of
aeromonas spp.

2. Introduction:-
Bacteria of the motile Aeromonas group occur widely in fresh and estuarine waters.They cause a
septicaemic infection in fishes and can be associated with gastrointestinal symptoms
Many motile aeromonads are psychrotrophic and such strains are capable of producing
enterotoxin and haemolysin at refrigeration temperatures It has been suggested that ingestion
of preformed toxin in food could induce gastrointestinal illness.
The pathogenic factors associated with Aeromonas are multifactorial and involve structural
components, siderophores, quorum-sensing mechanisms, secretion systems, extracellular
enzymes, and exotoxins.
motile aeromonads have the potential to contribute to their pathogenicity include the production
of endotoxins, extracellular enterotoxins, haemolysins, cytotoxins and proteases; the ability to
adhere to cells; and the possession of certain surface proteins.

3. Pathogenicity???
Pathogenicity refers to the ability of an
organism to cause disease (ie, harm the
host). This ability represents a genetic
component of the pathogen and the overt
damage done to the host is a property of
the host-pathogen interactions.

4. Mechanism of pathogenicity

6. Virulence factors and their modes of action
Aeromonas species produce a range of extracellular proteins including
proteases, nucleases, enterotoxins,haemolysins, and cytotoxins

8. 1)ENTEROTOXINS:-
These are extracellular products which may act on intestinal epithelium
Cytotonic enterotoxins
Cytotonic entertoxins stimulate cyclic adenosine 3',5'-monophosphate (cyclic amp)-mediated
sequences of events in cells. Cytotonic enterotoxin causes rounding of these cells and stimulates
steroidogenesis . A heat-stable, rapidly acting permeability factor was produced by most strains of
A. Hydrophila and A. Sobria. Cytotoxic enterotoxins
Cytotoxic enterotoxins
Cell damage or death, and produce dysentery-like symptoms.. In about 20% of infections with
enterotoxigenic strains of aeromonas there are dysenteric symptoms.
Fluid accumulation due to the action of enterotoxin is considered significant if there is an
intestinal weight : body weight ratio greater than 0.8.

9. 2)Haemolysins:-
Haemolysins are cytolytic extracellular proteins which act by forming holes in cell
membranes by inserting into the lipid bilayer, thus destroying the membrane
permeability barrier.
Among the biological activities associated with purified aerolysin are elicitation
of vascular permeability at the site of injury, oedema, and necrotic and lethal
activities
the ability of haemolysin-producing bacteria to release inflammatory mediators
from various cells. The release of these inflammatory mediators may be
responsible for the increased vascular permeability and oedema formation
associated with haemolysin, and aerolysin.

10. Proteases , Haemagglutinins &
endotoxin:-
3)Proteases may contribute to pathogenicity by causing direct tissue damage or enhanced invasiveness.They
may also have an indirect effect in A. hydrophila by bringing about the proteolytic activation of the aerolysin (B-
haemolysin) precursor.
4)Haemagglutinins are the surface features on bacterial cells which permit their attachment to receptor groups
on erythrocytes, Erythrocytes from different species may be used in this technique, and information on the
nature and specificity of the receptors on the eukaryotic cell surface can be obtained by testing various sugars
for their ability to inhibit haemagglutination
5)Endotoxins are the lipopolysaccharide component of the outer membrane of the cell, which, in many Gram-
negative pathogens, is toxic to man and animals. Endotoxin may play an important role in infections by
opportunistic pathogens like aeromonas spp,Endotoxin is much more heat-stable than protein toxins, and
consists of polysaccharide side chains, core polysaccharide, and lipid A, which is the component which confers
toxicity to the complex.

11. Commomn features of pathogenicity:-
40 Aeromonas strains from fishes showed that most of them were haemolytic.
Most of the strains studied produced haemolysin, protease, lecithinase, lipase and DNase.
Combinations of the inhibition patterns, thermostabilities and serological characteristics of the
proteases of motile Aeromonas species and of A. salmonicida were compared. Two distinct types
of extracellular proteases were found:
1. thermostable metallo-protease (TSMP), sensitive to EDTA and stable on heating at 56°C for 30
min, and
2. thermolabile serine protease (TLSP), sensitive to PMSF and to heating at 56°C for 30 min
Of 47 strains tested, 27 produced both proteases, 19 produced only TSMP, and one produced
only TLSP (which is the major protease in A. salmonicida)

12. The role of attachment in pathogenesis:-
The ability to attach to host cells allows for the maximum effect of any toxins that an organism
may produce, and is a prerequisite for successful invasion. Where bacteria produce enterotoxins
which cause excessive secretion of water and electrolytes from the mucosa of the small bowel,
colonization factor antigens (CFAs) which permit specific adhesion of pathogens to target cells,
are equally important virulence factors.
Ability of bacteria to agglutinate erythrocytes is a simple method of detecting whether bacteria
can attach to cells of potential host species. Found evidence for a variety of attachment
mechanisms in Aeromonas strains.

13. Type iii secretion system:-
strains possess a type III secretion system (T3SS), which enables many pathogenic gram-negative
81 bacteria to secrete and inject pathogenicity proteins (effectors) into the cytosol of eukaryotic
cells via 82 needle-like structures called needle complexes or inject isomes. T3SS was first
identified in pathogenic 83 strains of Yersinia spp. (Michiels et al. 1990). In Aeromonas T3SS has
been identified in A. 84 salmonicida, A. caviae, A. veronii bv. Sobria and A. hydrophila . Since this
mechanism correlates with bacterial pathogenicity, its presence is used as a general 86 indicator
of bacterial virulence.

16. Pathogenecity of A. hydrophila:-
A. hydrophila strains with enhanced virulence for fish showed serum resistance, autoaggregation, and
serotypic properties suggesting that their surface structure, especially the lipopolysaccharides (LPS)
differed from that of other strains. These strains had distinct morphological and antigenic properties ,
ECPs of two A. hydrophila strains: one virulent, and one weakly virulent for fish. The less virulent strain
showed 20-fold greater production of haemolysin and eight-fold greater production of enterotoxin than
the virulent strain, while both produced equal amounts of a dermonecrotic factor. Purified haemolysin was
found to be non-toxic for fish. virulence to fish in vivo indicated that 8-haemolysin, though toxic, does not
play a role in the pathogenicity of A. hydrophila infection.
A. hydrophila produces and exports haemolysin in an inactive form which it is processed extracellularly by
protease to the active form. Another role is to facilitate the access of other enzymes to their targets. Thus
mutations in protease activity may affect the activity of haemolysin and other toxins and may indirectly
affect virulence determinations.

17. Surface layer:-
The surface array matrix i.e, surface structure of A. hydrophila influence the interaction between
bacterial cell and its environment.
Adhesins
Pathogen shows chemotaxis towards gut (mucus) and the pathogen has the ability to attch
selected host cell like erythrocytes, and tissue proteins like collagen, fibronectin, glycoprotein
and serum proteins by action of adhesins. (43kDa) shown to have high homology to two OMPs
appear to be extremely selective, recognising D-mannose & L-fructose side chain on polymers
located on the surface of eukaryotic cell.this seems to be important in invasion of epithelial cells
invitro.
Extracellular products(ecp)
Enzymes – hemolysin, protease, 64kDa serine protease, metallo protease , acetylcholinesterase
(15.5 kDapp) Isolates with aerolysins(aerA), cytotoxic enterotoxins (alt) and serine protease
genes were most frequently virulent with LD50.

18. Aerolysin:-
Aerolysin is a soluble, hydrophilic protein which is exported from A. hydrophila as an inactive protoxin
which is subsequently reactivated by the removal of 25 amino acids
This small domain apparently prevents aggregation of the aerolysin molecules. There are at least
three stages in the disruption of erythrocytes by aerolysin.
1. Binding-both the protoxin and aerolysin can bind to receptors on the cell surface. The receptor for
aerolysin in the rat RBC membrane is glycophorin, a glycoprotein which spans the RBC membrane and
has an internal hydrophobic end which reacts with membrane lipids, and an external nhydrophilic end
exposed to the external environment. It has attached oligosaccharides at the outer surface of the
membrane.
2. Aggregation of toxin-after binding the active form can aggregate rapidly to form discrete holes 2
nm in diameter.
3. The state which results in cell disruption. This stage is still somewhat unclear. The aggregation may
be necessary to ‘generate a conformation or expose a domain’ which will allow penetration of the
lipid bilayer

19. Pathogenicity of a. jandeii:-
Possible ecp activity which was equated with production of caseinase, collagenase, elastase,
protease, lipase and haemolysins.
Pathogenicity of A. sorbia
Role of caseinase, haemolysins and cytotoxins, enterotoxins, haemaggultinins, etc

20. Pathogeneicity of A. salamonicida:-
Possesion of an extra cellular (A) layer, a type III secretion system and production of ECP.
A layer
A layer is thought to be product of single chromosomal gene invivo. With a virulence array
protein gene A (vap A) . A layer have an insulin binding capacity may confer protection against
phagocytosis thus destruction by macrophages.
It also constitute a macromolecular refractive protein barrier essential for virulence.
Hydrophobic A layer provides an affinity to bind fatty acid esters of polyethylene glycol.
A layer constitute first line defence defence for A.salmonicida .

21. Outer membrane proteins:-
76 unique proteins identified including dominant S layer Vap proteins , 10 porins ,
phosphoglycerate kinase, enolase and receptors involved in nutrient acquisition.
Capsule formation which help in adherence to the host.
Haemeaggultinins
Adhesins

22. Extracellular products:-
ADP ribosyltransferase toxin(AexT) acetylcholinoestearase, several protease like two
metalloprotease i,e 37kDa leucine aminopeptidase and 30kDa metalloprotease 3.
70kDa serine protease, 56kDa haemolysins and 100kDa unidentified proteins in the ECP.
Metallo caseinase (AsaP1 ) linled with lethal toxicity of A. salmonicida.
LPS free phospholipase help in injection

23. Scavenging for iron
It successfully scavenge for iron in iron limited condition there is an evidence of production of
IROMP
A layer were capable of sequestering iron. As it has a iron uptake mechanism from host cell,
being a binding site of porphyrins.

25. Thank you..