Download Bacterial disease

Bacterial disease
Pathogen and the
host
Pathogens

Pathogenic bacteria are capable of
causing disease
Infectious disease – change of structure
or function of a host caused by
microbes
 This change is manifested with a set of
symtoms (pain, fever, redness,
swelling)

Infection

The establisment and multiplication of
bacteria on the site in the host

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Systemic - bacteria are spread throughout
the body
Sepsis - the presence of bacteria or their
products in the blood or tissues
Septicemia -the multiplication of bacteria in
the blood
Toxemia- the presence of a bacterial toxin in
the blood
Infection II
Asymptomatic carriage – patogens
are present without the production
of any symptoms
 Clononization – the establishment
and multiplication of bacteria on a
site (mucuse membranes) of thehost

Virulence factors of
pathogens

The features of bacteria that alow
them to:
invade and remain with the host,
 acquire nutrients,
 avoid or demage the host immune
system
 spread between hosts

Pathogenicity
Thrue pathogens (B.anthracis) are
capable of infecting healthy hosts
 Oportunistic pathogens
(Pseudomonas aeruginosa) are
capable of infecting hosts which are
damaged (immunocompromised by
another infection)

Normal flora or commensals

Presence in the body is normally
beneficial to the host

Resident microflora on a site in the host
gastrointestinal tract
genito-urinary tract (vagina)
respiratory tract
skin
The nature of bacterial
disease
Bacillus athracis was proven to be a
causative agent for anthrax (1870
Robert Koch)
 The etiologies (causes) of many
diseases in animal were shown to be
a result of bacterial infection

The nature of bacterial
disease
The symptoms of the disease depen
on the site of infection, toxic
products of pathogens and the
abbility of the host to combat the
immune system
 Disease may be acute or chronic or
asymptomatic

The nature of bacterial
disease
Bacteria are capable of cuaisng:
 1) just one kind of diseases as swine
dysentery (Brachispira
hyodysenteriae)
 2) range of different diseases in
many host species (Staphylococcus
aureus)

Koch´postulates
How to identify the causative agent
and establish how it causes disease
 The relationship between a
bacterium and a observed disease
has been established if the
candidate bacterium fulfils all criteria
laid down by Robert Koch

Koch´postulates

1.The bacteria should be foound in
all cases and at all sites of the
disease

2. The bacteria should be isolated
from the infected host and
mantained in pure culture
Koch´postulates

3)The pure culture microbe should
cause symptoms of the disease on
on inoculation into a susceptible
individual (animal model)

4)The bacteria shoul be reisolated
from the intentionaly infected host
Entry and colonization of
animal hosts
Overview

Bacterium must reach the site at
wich it can survive, accumulate
nutrents to allow it to replicate
Transmission between hosts
Air/aerosols
 Food/water borne
 Direct contact

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Sexual transmission
Vectore –borne (Borrelia sp.)
 Microbes may remain on surfaces or
penetrate throught into the tissues

Colonization of surfaces
Adhesion – adhesion molecules on
the surface of the host cells bind to
the microbial adhesins (proteins,
polysachrides ..)
 Motility and mucinases break down
mucous

Invasion of host cells

Invasins induce non-phagocytic cells
to také up bacteria
Intracellular parasites
 Possibility to penetrate throught
epitelial layers and to spread within
the host

Acquisition of nutrients

For example iron –chelating
proteins (siderofors) alow the
bacteria to compete with the host
for iron (in lactoferin)
Salmonella Typhimurim
 Listeria monocytogenes

Spread of bacteria

Extracellular enzymes and toxins
which destroy host tissue alow the
dissemination of the pathogen in
the host

hyaluronidase (S. aureus)
Avoidance of host defense
mechanisms

Phagocytes
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listeriolysin O (L. monocytogenes) breaks
down the phagosome membranes allowin
the bacteria to escape into the cytoplasm
Antibodies
Protein A (S.aureus)
Sialic acid in capsules not recognised as
foregin