This document discusses microbial pathogenesis and infection. It begins by defining key concepts like infection, infective process, and infection disease. It then describes the normal relationships between microorganisms and the human body, including symbiosis, commensalism, mutualism, and parasitism. The document goes on to classify microbial parasitism and characterize the spread of infection through reservoirs, transmission routes, and vectors. It also examines the infectious process, virulence factors that promote microbial growth, and the roles of exotoxins and endotoxins produced by pathogens.

1. DOCTRINE ABOUT INFECTION

2. • Studies the properties of microorganisms
that provide their viability in the
macroorganism and their ability to produce a
pathogenic effect on it.
• It also studies the defense and adaptation
reaction of the macrooganism to this effect.

3. In fact, the presence of some microorganisms can even benefit the host. Therefore,
before we discuss the role of microorganisms in causing disease, let’s examine the
relationship of microorganisms to the healthy human body.
Relationships between the Normal Microbiota and the Host
Neutralism, when the partners do not produce any effect on one another.
The relationship between the normal microbiota and the host is called symbiosis, a
relationship between two organisms in which at least one organism is dependent on the
other:
a) Commensalism- one of the organisms benefits, and the other is unaffected
b) Mutualism – is a type of symbiosis that benefits both organisms
c) Parasitism – relationship between two species, in which one benefits at the
expense of the other, sometimes without killing it.
! Although categorizing symbiotic relationships by type is convenient, keep in mind that
the relationship can change under certain conditions

4. CLASSIFICATION AND CHARACTERIZATION OF
MICROBIAL PARASITISM
Obligate parasites are unable to exist outside the host’s body, as they had lost
all their need in food only in an intracellular kind of existence (Rickettsia,
Chlamydia, viruses etc.).
- Obligate intracellular parasites penetrate into a cell and multiply.
-Obligate extracellular parasites attach to cell surface and spread along
intercellular areas.
Facultative parasites are able to exist for some time in the environment, i.e.
outside the host’s body.
- Facultative intracellular parasites can live and multiply both inside a cell
and in on intracellular area (pathogens of tuberculosis, gonorrhea,
meningococcal infection etc.)
- Saprophytes are microorganism, which utilize dead organics substrates. On
getting into a human body some of them may lead a parasitic mode of live, i.e.
become pseudoparasites. But this phenomenon is sporadic

5. • Infection is a totality of the processes arising in an interaction between
the micro – and macroorganism. Infection is the invasion or colonization
of the body by pathogenic microorganisms
• Infective (infections) process is a totality of pathological, physiological,
reparatory and other responses of the macrooganism to the intrusion of
a pathogenic microorganism.
• Infection disease is a totality of clinical and laboratory symptoms that
arise as a result of responses to the intrusion of a microorganism.
Disease occurs when an infection results in any change from a state of
health
• Symptoms, or changes in body function, such as pain and malaise. These subjective
changes aren’t apparent to an observer. The patient can also exhibit signs, which are
objective changes the physician can observe and measure. Frequently evaluated signs
include lesions (changes produced in tissues by disease), swelling, fever, and paralysis. A
specific group of symptoms or signs may always accompany a particular disease; such a
group is called a syndrome.

6. KOCH’S POSTULATES
THEY ARE SUMMARIZED AS FOLLOWS:
1.The same pathogen must be
present in every case of the
disease.
2.The pathogen must be
isolated from the diseased host
and grown in pure culture.
3.The pathogen from the pure
culture must cause the disease
when it’s inoculated into a
healthy, susceptible laboratory
animal.
4.The pathogen must be
isolated from the inoculated
animal and must be shown to
be the original organism.

7. The prevalence of a disease is the number of people in apopulation who develop a disease at a
specified time, regardless of when it first appeared
• If a particular disease occurs only occasionally, it is called a sporadic disease (typhoid fever).
• A disease constantly present in a population is called an endemic disease (common cold).
• If many people in a given area acquire a certain disease in a relatively short period, it is called an
epidemic disease (influenza)
• An epidemic disease that occurs worldwide is called a pandemic disease (Covid 19)
Another useful way of defining the scope of a disease is in terms of its severity or duration.
• An acute disease is one that develops rapidly but lasts only a short time; a good example is
influenza.
• A chronic disease develops more slowly. The body’s reactions may be less severe, but the disease is
likely to continue or recur for long periods. Infectious mononucleosis, tuberculosis, andhepatitis B fall
into this category.
• A subacute disease - disease that is intermediate between acute and chronic is described as a; an
example is subacute sclerosing panencephalitis, a rare brain disease characterized by diminished
intellectual function and loss of nervous function.
• A latent disease is one in which the causative agent remains inactive for a time but then becomes
active to produce symptoms of the disease; an example is shingles, one of the diseases caused by
varicella virus.

8. Infections can also be classified according to the extent to which the host’s body is
affected.
• A local infection is one in which the invading microorganisms are limited to a relatively
small area of the body. Some examples of local infections are boils and abscesses.
• In a systemic (generalized) infection, microorganisms or their products are spread
throughout the body by the blood or lymph. Measles is an example of a systemic infection.
• Very often, agents of a local infection enter a blood or lymphatic vessel and spread to
other specific parts of the body, where they are confined to specific areas of the body. This
condition is called a focal infection. Focal infections can arise from infections in areas
such as the teeth, tonsils, or sinuses.
• Sepsis is a toxic inflammatory condition arising from the spread of microbes, especially
bacteria or their toxins, from a focus of infection.
• Septicemia, also called blood poisoning, is a systemic infection arising from the
multiplication of pathogens in the blood. Septicemia is a common example of sepsis.
• The presence of bacteria in the blood is known as bacteremia.
• Toxemia refers to the presence of toxins in the blood (as occurs in tetanus)
• Viremia refers to the presence of viruses in blood

9. A definite sequence of events usually occurs during infection and disease. For an infectious disease to occur, there
must be a reservoir of infection as a source of pathogens. Next, the pathogen must be transmitted to a susceptible
host by direct contact, by indirect contact, or by vectors. Transmission is followed by invasion, in which the
microorganism enters the host and multiplies. Following invasion, the microorganism injures the host through a
process called pathogenesis.
Development of Disease
Incubation Period is the interval between the initial infection and the first appearance of any signs or symptoms.
Prodromal Period is a relatively short period that follows the period of incubation in some diseases. The prodromal
period is characterized by early, mild symptoms of disease, such as general aches and malaise.
Period of Illness - during the period of illness, the disease is most severe. The person exhibits overt signs and
symptoms of disease, such as fever, chills, muscle pain (myalgia), sensitivity to light (photophobia),
sore throat (pharyngitis). If the disease is not successfully overcome (or successfully treated), the patient dies during
this period.
Period of Decline - during the period of decline, the signs and symptoms subside. The fever decreases, and the
feeling of malaise diminishes. During this phase, which may take from less than 24 hours to several days, the patient
is vulnerable to secondary infections.
Period of Convalescence - during the period of convalescence, the person regains strength and the body returns to
its prediseased state.

10. THE SPREAD OF INFECTION
Reservoirs of Infection
Human Reservoirs - people with signs and symptoms nof a disease may transmit the
disease; in addition, some people can harbor pathogens and transmit them to others without
exhibiting any signs of illness. These people, called carriers, are important living reservoirs
of infection – Anthroponoses
Animal Reservoirs - both wild and domestic animals are living reservoirs of microorganisms
that can cause human diseases. Diseases that occur primarily in wild and domestic animals
and can be transmitted to humans are called zoonoses or zooanthroponoses
Nonliving Reservoirs - the two major nonliving reservoirs of infectious disease are soil
and water – Sapronoses

11. TRANSMISSION OF DISEASE
Routes of transmission
Contact transmission is the spread of a disease agent by direct contact, indirect contact,
or droplet transmission.
-Direct contact transmission, also known as person-to-person transmission, is the direct
transmission of an agent by physical contact between its source and a susceptible host
-Indirect contact transmission occurs when the agent of disease is transmitted from its
reservoir to a susceptible host by means of a nonliving object.
-Droplet transmission is a third type of contact transmission in which microbes are spread
in droplet nuclei (mucus droplets) that travel only short distances.
Vehicle transmission is the transmission of disease agents by a medium, such as water,
food, or air (waterborne transmission, foodborne transmission, airborne transmission)
Vectors - arthropods (tick) are the most important group of disease vectors— animals that
carry pathogens from one host to another.
Intrauterine or placental
Vertical - when the fetus passes through the infected birth canal of the mother.

14. THE ROLE OF MICROBES IN THE INFECTIOUS
PROCESS
Pathogenicity is the potential ability of microbes to cause an infectious process.This is a specific,
genetically determined trait.
According to the degree of pathogenicity, all microbes are divided into 3 groups:
1 - non-pathogenic or saprophytes,
2 - conditionally pathogenic or potentially pathogenic,
3 – pathogenic.
Virulence is the individual property of a given strain of microbe to cause the development of an
infectious process.This is a measure of pathogenicity, its quantitative and qualitative characteristics,
the phenotypic manifestation of the genotype of pathogenic microbes.
There are:
1 - highly virulent,
2 - moderately virulent,
3 - slightly virulent,
4 - avirulent.

15. DETERMINATION OF VIRULENCE
• DLm (dose lethal minima) is a minimal
lethal dose for microorganisms or their
toxins, which may cause death of a test
animal within a definite time period. It is a
relative value, depending on an animal
species.
• LD50 (doses lethal 50%) is an amount of
microorganisms or their toxins causing
death of 50% of the infected test animals.
• LD100 (dose certainly lethal) is an
absolute lethal dose, i.e. an amount of
microorganisms or toxins, causing death
of 100% of the infected test animals.
• Infections dose (ID) is a minimal amount
of pathogenic microorganisms that cause
an infectious disease in a definite number
of test animals

16. VIRULENT BACTERIAL (PATHOGENS) HAVE MECHANISMS THAT
PROMOTE THEIR GROWTH IN THE HOST AT THE EXPENSE OF THE
HOST AND TISSUE FUNCTIONS.
The virulence factors (factors of pathogenicity) are divided in:
1. factors of adhesion and colonization are factors of microorganism attachment on
sensible cell and ability to inhabit the foci of initial invasion.
2. factors of invasion or invasiveness are of penetration and distribution in
macroorganism;
3. factors of aggression or aggressiveness are factors of confrontation to the defense
mechanisms of the macroorganism;
4. factors of toxigenecity or toxin formation denote ability to generate exotoxins and
endotoxins.

17. FACTORS OF ADHESION AND COLONIZATION:
-fimbria (of the 1st order);
- proteins of an outer membrane
(adhesive proteins);
- lipopolysaccharides, lipoteichoic
acids of cell wall;
- other structures, which may be on
the surface of microbe or be part of
capsules and a cell wall;
- factors of chemotaxis and mobility.

18. FACTORS OF INVASION OR "SPREADING FACTORS"
- is a term for designation for a
family of bacterial enzymes which
disrupt the host cells of tissue and
intracellular spaces (exoenzymes
of microorganisms)
• Hyaluronidase
• Neuraminidase (sialidase)
• Fibrinolysin
• DNA-ase
• Collagenase
• Lecithinase (phospholipase)
• Proteases
• Hydrolysates

19. FACTORS OF AGGRESSION
- Are enhance resistance of
microorganisms to defense ability of
the macroorganism
• capsule;
• plasmocoagulase;
• Catalase and superoxidismutase
(oxidase);
• Aminopeptidase;
• Proteases;
- Protein A (in staphylococci),
protein M (in streptococci), V-W-
antigens (in plague pathogen);
• other factors : peptidoglycan,
techoic acids and other
components of a cell wall

20. FACTORS OF TOXIGENECITY OR TOXIN-FORMATION
• Toxin are either metabolic
products of a microbial cell –
exotoxins (grampositive,
gramnegative bacteria), or
integral components of a cell
wall (!!! Gramnegative
bacteria), that are released as a
result of its destruction –
endotoxins, that bring in
disorder into the life of the
macroorganism

22. EXOTOXINS
• are secretory proteins substances with
fermentative activity, which are produced by a
microbial cell. Exotoxins may produce gram-
positive and gram-negative microorganisms.
Exotoxins are thermolabile, they are highly
specific in action. They are responsible for
the clinical manifestations of an infection
process, can act at distance, far from the
focus of infection. Their effect is highly toxic
(9 kg of botulotoxin can kill the whole
mankind). They exhibit high immunogenicity;
in response to their injection specific
antibodies originate to neutralize to their
effect (when treated with formalin exotoxins
get detoxicated and are transformed into
antitoxins or toxoid, which are devoid of toxic
properties, but maintain an ability to induce
antitoxic antibodies).

23. CLASSIFICATION OF EXOTOXINS
• By molecular arrangement:
• complex, which are composed of two
fragments A and B. B-fragment interact
with the receptors of sensible cell,
adheres on its surface and forms a
transmembraneous canal, through which
A-fragment, the toxin proper, penetrates
into sensible cell and exhibits its toxic
properties.
• plain (simple) – are “incised” exotoxins.
They synthesize in a bacterial cell as
protoxins and, when are cut into A and B
fragment by protease they get
transformed into active - forms.

24. • By an extent of binding with a bacterial
cell:
A-group – are those, which are secreted
into an external (environment);
B-group – are partly secreted into the
environment and partially bound with a
bacterial cell;
C-group – those that are bound with a
bacterial cell and released only after its
death/
• By the nature of targets:
neurotoxin – which damage nerve cells;
hemolysins, which destroy erythrocytes;
enterotoxins, which affect the cells of the
gastrie epithelium;
dermstotoxins – affecting the skin cells;
leucocydines – affecting leucocytes,
neutrophils and phagocytes.

28. - pyrogenic effect (elevation of body
temperature), because endotoxin
induces realize of interleukin-1 from
macrophages, which effects the center
of thermoregulation;
- a toxic effect on the vessels, as
endotoxin enhances permeability of a
vascular wall. This result in a hypotonic
effect in severe cases a collaptoid state.
- stimulating effect on the blood-
coagulation system, as it activates
Hageman’s factors (factor XII of the
blood-coagulation system). This
condition is associated with
microthrombs and impaired
microcirculation (is severe cases the
syndrome of disseminated intravascular
coagulation (DIC-syndrome)
- cardio – and hepatoxic effect blocks
the respiratory function of mitochondria
in the heart and liver;
- membranolabilizing effect – influence
mast cell and basophils. This leads to
histamine and serotonin release and,
as a result, to allergic reaction;
- effect upon the immune system. In large
doses, at the peak of an infection
process it suppresses the functions of
the immune system. In small doses,
during convalescence, it stimulates
these functions. It also activates the
complement system into an alternative
way and stimulates interferon
production.
ENDOTOXINS

30. Thanks for your attention!