M
MICROBIOLOGY & PARASITOLOGY
C3
PREFINALS BACTERIA AND DISEASE
Disease
- result of an undesirable relationship between
the host and the pathogen, marked interruption
in the normal functioning of a body part or parts
Infection
- invasion of the body by pathogenic
microorganisms. The term is not synonymous
with disease
Symbiosis
- prolonged and close interaction between
organisms of different species.
Mutualism
- form of symbiosis in which both organisms
benefit from the relationship
Commensalism
- form of symbiosis in which one organism
benefits from another organism without causing
harm to it.
Parasitism
- form of symbiosis where one organism benefits
from another organism and the same time
causes harm to the other
Pathogenicity
- ability of an organism to produce disease. An Postulates
organism that can produce disease in humans is 1. The suspected organism must be absent in
said to be pathogenic healthy individuals but present in those with
Virulence the disease.
- describes the degree of pathogenicity of an 2. The suspected organism must be isolated
organism or the degree to which an organism from the infected host and grown in pure
can produce disease culture.
Contamination 3. The organisms grown from pure culture must
- presence of unwanted materials where they produce the same disease as that of the
should not be or at concentrations above the infected source when inoculated to a
normal susceptible animal.
- may not necessarily lead to harm 4. The same organism must be isolated from
Pollution pure culture from the experimentally-infected
- presence of contaminants that can cause host.
adverse biological effects to humans and
communities. NOTE
- All pollutants are contaminants but not all Once all the above conditions are fulfilled, it can
contaminants are pollutants. now be concluded that the organism isolated is
Bacteremia indeed the cause of the disease under study
- presence of bacteria in the blood.
Septicemia Limitations of Koch’s Postulates
- presence of actively multiplying bacteria in the there are certain organisms that cannot be
blood, usually from a source of infection. artificial culture media.
- The condition is called sepsis o Viruses are obligate intracellular
Pyemia parasites that need to be living cells.
- presence of pus-producing bacteria in the o Mycobacterium leprae, the causative
bloodstream agent of leprosy needs to be grown o
Viremia foot pads of mice and armadillo
- presence of viruses in the blood not all people who acquire an infection
Toxemia develop overt disease.
- presence of toxins in the blood o Most of the time, infections are sub-
clinical.
KOCH’S POSTULATES o the reaction of humans to specific
- Robert Koch greatest and most well-known pathogens may differ given a specific
contribution was proving that certain microorganism.
microorganisms caused specific diseases. o human beings have different genetic
- Together with some of his colleagues, he compositions that may modulate their
developed a scientific experimental procedure responses to the same organism.
to prove this relationship. o One individual might develop minor
- This experimental procedure was published in
illness from a particular pathogen but
1884 and came to be known as Koch's
the same pathogen may produce fatal
postulates.
infection in another host
there are certain organisms that are
species- specific.
Hannah Adan 1
, M
MICROBIOLOGY & PARASITOLOGY
C3
PREFINALS BACTERIA AND DISEASE
o There are organisms that produce o Water serves as a reservoir for
disease only in animals in the same Entamoeba histolytica, a protozoan
manner that there are infectious agents parasite that cause amoebiasis.
that produce disease only in humans. o Aquatic vegetation such as watercress
o organisms that produce disease only in and "kangkong" harbor Fasciola
humans cannot be tested using hepatica larvae which causes damage to
laboratory animals and vice versa. the liver.
Portal of exit
- where the infectious agent is commonly located
FACTORS INFLUENCING THE OCCURRENCE OF or localized.
INFECTION - For example, the blood fluke Schistosoma
Chain of Infection haematobium which preferentially infects the
- The development of an infectious disease is a urinary bladder exits the host via urine.
consequence of the interaction among three - Infectious agents causing respiratory tract
components-the etiologic agent, the host, and infection will leave the host via droplets or
the environment. aerosols from the respiratory secretions.
Reservoir Sexually transmitted infectious agents exit via
- Reservoirs serve as the continual source of vaginal or urethral the causative agent of
disease-producing microorganisms. malaria
- the site where an infectious agent normally - There are also organisms that exit the host
resides and multiplies. through blood-sucking arthropods such as
- provides the organisms with conditions that Plasmodium tract.
enable them to survive and multiply and provide Mode of transmission
opportunity for transmission to a susceptible Direct Contact
host. 1. Person – person Contact
Animal Reservoirs - involves transmission through skin-to-
- zoonotic infections. skin contact, kissing, or sexual
o Certain infectious diseases can be transmission.
transmitted from an animal to humans. - Warts can be transmitted through direct
- In most instances, humans serve only as an contact with the lesion on the skin of
incidental host and dead-end host and thus the infected persons.
disease will not be transmitted to another - Infectious mononucleosis caused by
human. Epstein Barr Virus is transmitted through
Human Reservoir saliva, hence the name "Kissing Disease."
- may be directly transmitted from one individual Syphilis, gonorrhea, and other sexually
to another. transmitted infections are spread through
- human reservoir may not necessarily manifest vaginal and urethral secretions of
with the disease. infected persons
- Carriers. 2. Droplet Spread
o those who developed the disease, got - patients with respiratory tract infection such as
well but still harbor the organism the common colds or influenza can transmit the
thereby transmitting them to others. causative agents during coughing and sneezing.
o are individuals who are not aware that - Droplets are differentiated from aerosols by its
they a transmitting the infectious agent larger size (> 5 microns in size).
which makes them public health hazards - It is considered as direct contact because the
o asymptomatic or healthy carriers droplets are sprayed over a few feet before they
o Those who are infected but do not fall to the ground.
manifest symptoms are known as. - Close proximity with the source is necessary for
o incubatory carriers droplets to be transmitted
o Carriers who transmit the causative Indirect Contact
agent during the incubation period of 1. Airborne transmission
the illness. through dust or aerosols.
o Chronic carriers Aerosols are droplets with nuclei less
o are those who harbor the organism for than 5 microns in size.
Due to their small size, they may remain
months or longer after the patient
suspended in air for a longer time and
developed the initial infection.
may cover farther distance than droplets.
o convalescent carriers
There are also organisms that can be
o Individuals who developed the disease,
carried with dust. For example, the
recovered but remain capable of fungus Cryptococcus neoformans can be
transmitting the causative agent transmitted through aerosolized pigeon
Environmental Reservoir or fowl droppings and inhaled by a
- Water, soil, and plants can harbor infectious susceptible host.
organisms. Measles, a common childhood illness, can
o soil be transmitted through aerosols
o fungus Histoplasma capsulatum is 2. Vehicle transmission
associated with soil. refers to transmission of organisms
o water through media such as food, water, milk,
Hannah Adan 2
MICROBIOLOGY & PARASITOLOGY
C3
PREFINALS BACTERIA AND DISEASE
Disease
- result of an undesirable relationship between
the host and the pathogen, marked interruption
in the normal functioning of a body part or parts
Infection
- invasion of the body by pathogenic
microorganisms. The term is not synonymous
with disease
Symbiosis
- prolonged and close interaction between
organisms of different species.
Mutualism
- form of symbiosis in which both organisms
benefit from the relationship
Commensalism
- form of symbiosis in which one organism
benefits from another organism without causing
harm to it.
Parasitism
- form of symbiosis where one organism benefits
from another organism and the same time
causes harm to the other
Pathogenicity
- ability of an organism to produce disease. An Postulates
organism that can produce disease in humans is 1. The suspected organism must be absent in
said to be pathogenic healthy individuals but present in those with
Virulence the disease.
- describes the degree of pathogenicity of an 2. The suspected organism must be isolated
organism or the degree to which an organism from the infected host and grown in pure
can produce disease culture.
Contamination 3. The organisms grown from pure culture must
- presence of unwanted materials where they produce the same disease as that of the
should not be or at concentrations above the infected source when inoculated to a
normal susceptible animal.
- may not necessarily lead to harm 4. The same organism must be isolated from
Pollution pure culture from the experimentally-infected
- presence of contaminants that can cause host.
adverse biological effects to humans and
communities. NOTE
- All pollutants are contaminants but not all Once all the above conditions are fulfilled, it can
contaminants are pollutants. now be concluded that the organism isolated is
Bacteremia indeed the cause of the disease under study
- presence of bacteria in the blood.
Septicemia Limitations of Koch’s Postulates
- presence of actively multiplying bacteria in the there are certain organisms that cannot be
blood, usually from a source of infection. artificial culture media.
- The condition is called sepsis o Viruses are obligate intracellular
Pyemia parasites that need to be living cells.
- presence of pus-producing bacteria in the o Mycobacterium leprae, the causative
bloodstream agent of leprosy needs to be grown o
Viremia foot pads of mice and armadillo
- presence of viruses in the blood not all people who acquire an infection
Toxemia develop overt disease.
- presence of toxins in the blood o Most of the time, infections are sub-
clinical.
KOCH’S POSTULATES o the reaction of humans to specific
- Robert Koch greatest and most well-known pathogens may differ given a specific
contribution was proving that certain microorganism.
microorganisms caused specific diseases. o human beings have different genetic
- Together with some of his colleagues, he compositions that may modulate their
developed a scientific experimental procedure responses to the same organism.
to prove this relationship. o One individual might develop minor
- This experimental procedure was published in
illness from a particular pathogen but
1884 and came to be known as Koch's
the same pathogen may produce fatal
postulates.
infection in another host
there are certain organisms that are
species- specific.
Hannah Adan 1
, M
MICROBIOLOGY & PARASITOLOGY
C3
PREFINALS BACTERIA AND DISEASE
o There are organisms that produce o Water serves as a reservoir for
disease only in animals in the same Entamoeba histolytica, a protozoan
manner that there are infectious agents parasite that cause amoebiasis.
that produce disease only in humans. o Aquatic vegetation such as watercress
o organisms that produce disease only in and "kangkong" harbor Fasciola
humans cannot be tested using hepatica larvae which causes damage to
laboratory animals and vice versa. the liver.
Portal of exit
- where the infectious agent is commonly located
FACTORS INFLUENCING THE OCCURRENCE OF or localized.
INFECTION - For example, the blood fluke Schistosoma
Chain of Infection haematobium which preferentially infects the
- The development of an infectious disease is a urinary bladder exits the host via urine.
consequence of the interaction among three - Infectious agents causing respiratory tract
components-the etiologic agent, the host, and infection will leave the host via droplets or
the environment. aerosols from the respiratory secretions.
Reservoir Sexually transmitted infectious agents exit via
- Reservoirs serve as the continual source of vaginal or urethral the causative agent of
disease-producing microorganisms. malaria
- the site where an infectious agent normally - There are also organisms that exit the host
resides and multiplies. through blood-sucking arthropods such as
- provides the organisms with conditions that Plasmodium tract.
enable them to survive and multiply and provide Mode of transmission
opportunity for transmission to a susceptible Direct Contact
host. 1. Person – person Contact
Animal Reservoirs - involves transmission through skin-to-
- zoonotic infections. skin contact, kissing, or sexual
o Certain infectious diseases can be transmission.
transmitted from an animal to humans. - Warts can be transmitted through direct
- In most instances, humans serve only as an contact with the lesion on the skin of
incidental host and dead-end host and thus the infected persons.
disease will not be transmitted to another - Infectious mononucleosis caused by
human. Epstein Barr Virus is transmitted through
Human Reservoir saliva, hence the name "Kissing Disease."
- may be directly transmitted from one individual Syphilis, gonorrhea, and other sexually
to another. transmitted infections are spread through
- human reservoir may not necessarily manifest vaginal and urethral secretions of
with the disease. infected persons
- Carriers. 2. Droplet Spread
o those who developed the disease, got - patients with respiratory tract infection such as
well but still harbor the organism the common colds or influenza can transmit the
thereby transmitting them to others. causative agents during coughing and sneezing.
o are individuals who are not aware that - Droplets are differentiated from aerosols by its
they a transmitting the infectious agent larger size (> 5 microns in size).
which makes them public health hazards - It is considered as direct contact because the
o asymptomatic or healthy carriers droplets are sprayed over a few feet before they
o Those who are infected but do not fall to the ground.
manifest symptoms are known as. - Close proximity with the source is necessary for
o incubatory carriers droplets to be transmitted
o Carriers who transmit the causative Indirect Contact
agent during the incubation period of 1. Airborne transmission
the illness. through dust or aerosols.
o Chronic carriers Aerosols are droplets with nuclei less
o are those who harbor the organism for than 5 microns in size.
Due to their small size, they may remain
months or longer after the patient
suspended in air for a longer time and
developed the initial infection.
may cover farther distance than droplets.
o convalescent carriers
There are also organisms that can be
o Individuals who developed the disease,
carried with dust. For example, the
recovered but remain capable of fungus Cryptococcus neoformans can be
transmitting the causative agent transmitted through aerosolized pigeon
Environmental Reservoir or fowl droppings and inhaled by a
- Water, soil, and plants can harbor infectious susceptible host.
organisms. Measles, a common childhood illness, can
o soil be transmitted through aerosols
o fungus Histoplasma capsulatum is 2. Vehicle transmission
associated with soil. refers to transmission of organisms
o water through media such as food, water, milk,
Hannah Adan 2
