Diseases and Infection
Identified as a disorder that affects an individual’s mental or physical well-being by the
World Health Organisation (WHO), a disease functions to impair or alter the normal
function of the human body. It can be classified into two categories; infectious, as it can
be transmitted from one individual to another and non-infectious, where it cannot be
spread through person to person contact (www.childfund.org.au).
Established as a sub-microscopic organism, a pathogen operates to infect a host,
subsequently causing illness and negatively affecting the anatomy of living beings, for
instance humans. The most commonly recognised microbes consist of
a. Bacteria
b. Fungus
c. Parasite
d. Protozoa
e. Virus
Bacteria
These unicellular prokaryotic microorganisms can be observed in every habitat on the
Earths surface, some even found in the interior or exterior of plants and animals. The
correspondence between organisms and bacteria can be beneficial and is said to be
symbiotic, in particular probiotics that aid the digestive system by keeping the gut
healthy. Conversely bacteria can also be pathogenic, discharging detrimental toxins that
cause disease in its host. The bacteria’s function is aided by its structure.
Surrounding the outer-layer of a bacterium is the capsule. Composed from
polysaccharides, this outer layer from drying out and becoming desiccated. It acts as a
virulence factor as the slippery layer hinders the process of phagocytosis, augmenting
the microbe’s capacity to cause illness.
Comprised from sugar and amino acids referred to as peptidoglycan, the cell wall
conserves the shape and structure of the bacteria.
Bacteria are considered to be prokaryotes; therefore, they don’t have any membrane-
bound organelles or a nucleus. Alternatively, they have an irregularly shaped region
where Deoxyribonucleic Acid (DNA) is retained. It also holds Ribonucleic Acid (RNA),
enzymes and proteins that are utilised for metabolic processes.
This particular microorganism us susceptible to genetic advantages, for instance,
antibiotic resistance due to circular-double-stranded DNA molecules in its structure
known as plasmids. Furthermore, it encompasses genes that facilitates the bacterium’s
survival. For example, if the host organism is being attacked, it will secrete toxins to kill
the offending organism.
The bacterial flagellum permits the movement of the prokaryotic organism.
1|Page
,Bacteria can come in multiple shapes, varying from spheres to rods, ranging from 0.2-2
micrometres in diameter and 1-8 micrometres in length. The three general shapes are:
a. Bacillus: Rod shaped, gram-positive bacteria.
b. Coccus: Spherical/Round shaped bacteria. Can be gram positive or
negative.
c. Spirillum: Cork-screw shaped, gram negative bacteria.
As previously stated, depending on their outer layer, bacteria can be:
i. Gram Positive – Consisting of a thick peptidoglycan layer, with no outer
lipid membrane. It will stain to become a crystal violet colour.
ii. Gram Negative – Consisting of a thin peptidoglycan layer and an outer
lipid membrane. It will stain to produce red colouring.
Figure 3 - An Illustration depicting Replication of Bacteria
Through a method of asexual reproduction that entails the division of a single entity into
two daughter cells, bacteria are able to multiply via a mechanism known as Binary
Fission. This transpires sequentially as:
i. The circular DNA and plasmids replicate.
ii. The cell grows in size and becomes bigger.
The circular DNA stands move to the opposite “poles” (ends) of the
cell.
iii. The cytoplasm begins to divide and new cell walls begin to form.
Cross walls begin to form around the replicated DNA.
iv. The cytoplasm divides and two daughter cells are formulated.
Each daughter cell has a copy of circular DNA, but a variable number of
plasmids.
Another form of asexual reproduction that enables bacteria to reproduce is through
spores, however this process is quite dormant and uncommon. Known as the
Temperature Danger Zone (TZD), bacteria will develop faster between 41°F (5°C) and
135°F (57°C) and perform best when the pH is neutral and the acid is low. Bacteria that
recreate via spores are usually in unfavourable conditions. The spores are inhaled
through the respiratory system, enter the lungs, and gain full access to the host causing
disease.
2|Page
, Figure 4- An Illustration depicting Bacterial Budding
Occurring in both multicellular and unicellular, bacteria can also multiply through
budding. A small bud will start to form in the exterior of the microbe, become a daughter
cell and separate from the parental cell. Chronologically:
i. A protuberance/swelling emerges from the bacterial cell.
ii. DNA and cytoplasm in the bacterium divides, the bud will receive the
copies.
iii. The bud enlarges in size, evolving into a new cell, a daughter cell. The
daughter cell will separate from its parent cell.
iv. The budding will result in a chain of bacterial cells.
Bacterial Disease
Listeriosis is a foodborne disease attained when an individual intakes a substance that is
contaminated with a gram-positive bacterium known as Listeria Monocytogenes. The
highest instances of this condition where found when the diagnosed digested
cooked/cured meat, poultry, sea food products and pre-prepared sandwiches and salads.
Essentially almost all ready-to-eat products.
When the Listeria monocytogenes is ingested, the bacteria replicated in the liver,
traveling through the body via the bloodstream invading many places, such as the brain,
intestines and spinal cord.
Listeria monocytogenes has a multifactorial virulence system. For instance, its ability to
grow at temperatures as low as 0oC permits the multiplication/replication at typical
refrigeration temperatures, greatly increasing its ability to invade human food.
Additionally, it has a thiol-activated hemolysin, listeriolysin O, that has been identified in
paying a crucial role in the organisms’ ability to multiply and spread from cell to cell.
This bacterial infection can be compartmentalised into two groups (www.who.int):
i. Non-Invasive Listeriosis (Febrile Listerial Gastroententis)
Considered to be a mild form, it affects relatively healthy individuals. The
period between exposure to an infection and the appearance of the first
symptoms is short, only a few days.
Symptoms are inclusive to muscle pain, diarrhoea, headaches and fever.
ii. Invasive Listeriosis
Considered to be a more oppressive, this form affects high-risk individuals in
the general population., such as infants, the elderly, pregnant woman, people
undertaking treatment for aids, or organs transplants.
Symptoms are inclusive of muscle pain, meningitis, septicaemia, and fever.
3|Page
Identified as a disorder that affects an individual’s mental or physical well-being by the
World Health Organisation (WHO), a disease functions to impair or alter the normal
function of the human body. It can be classified into two categories; infectious, as it can
be transmitted from one individual to another and non-infectious, where it cannot be
spread through person to person contact (www.childfund.org.au).
Established as a sub-microscopic organism, a pathogen operates to infect a host,
subsequently causing illness and negatively affecting the anatomy of living beings, for
instance humans. The most commonly recognised microbes consist of
a. Bacteria
b. Fungus
c. Parasite
d. Protozoa
e. Virus
Bacteria
These unicellular prokaryotic microorganisms can be observed in every habitat on the
Earths surface, some even found in the interior or exterior of plants and animals. The
correspondence between organisms and bacteria can be beneficial and is said to be
symbiotic, in particular probiotics that aid the digestive system by keeping the gut
healthy. Conversely bacteria can also be pathogenic, discharging detrimental toxins that
cause disease in its host. The bacteria’s function is aided by its structure.
Surrounding the outer-layer of a bacterium is the capsule. Composed from
polysaccharides, this outer layer from drying out and becoming desiccated. It acts as a
virulence factor as the slippery layer hinders the process of phagocytosis, augmenting
the microbe’s capacity to cause illness.
Comprised from sugar and amino acids referred to as peptidoglycan, the cell wall
conserves the shape and structure of the bacteria.
Bacteria are considered to be prokaryotes; therefore, they don’t have any membrane-
bound organelles or a nucleus. Alternatively, they have an irregularly shaped region
where Deoxyribonucleic Acid (DNA) is retained. It also holds Ribonucleic Acid (RNA),
enzymes and proteins that are utilised for metabolic processes.
This particular microorganism us susceptible to genetic advantages, for instance,
antibiotic resistance due to circular-double-stranded DNA molecules in its structure
known as plasmids. Furthermore, it encompasses genes that facilitates the bacterium’s
survival. For example, if the host organism is being attacked, it will secrete toxins to kill
the offending organism.
The bacterial flagellum permits the movement of the prokaryotic organism.
1|Page
,Bacteria can come in multiple shapes, varying from spheres to rods, ranging from 0.2-2
micrometres in diameter and 1-8 micrometres in length. The three general shapes are:
a. Bacillus: Rod shaped, gram-positive bacteria.
b. Coccus: Spherical/Round shaped bacteria. Can be gram positive or
negative.
c. Spirillum: Cork-screw shaped, gram negative bacteria.
As previously stated, depending on their outer layer, bacteria can be:
i. Gram Positive – Consisting of a thick peptidoglycan layer, with no outer
lipid membrane. It will stain to become a crystal violet colour.
ii. Gram Negative – Consisting of a thin peptidoglycan layer and an outer
lipid membrane. It will stain to produce red colouring.
Figure 3 - An Illustration depicting Replication of Bacteria
Through a method of asexual reproduction that entails the division of a single entity into
two daughter cells, bacteria are able to multiply via a mechanism known as Binary
Fission. This transpires sequentially as:
i. The circular DNA and plasmids replicate.
ii. The cell grows in size and becomes bigger.
The circular DNA stands move to the opposite “poles” (ends) of the
cell.
iii. The cytoplasm begins to divide and new cell walls begin to form.
Cross walls begin to form around the replicated DNA.
iv. The cytoplasm divides and two daughter cells are formulated.
Each daughter cell has a copy of circular DNA, but a variable number of
plasmids.
Another form of asexual reproduction that enables bacteria to reproduce is through
spores, however this process is quite dormant and uncommon. Known as the
Temperature Danger Zone (TZD), bacteria will develop faster between 41°F (5°C) and
135°F (57°C) and perform best when the pH is neutral and the acid is low. Bacteria that
recreate via spores are usually in unfavourable conditions. The spores are inhaled
through the respiratory system, enter the lungs, and gain full access to the host causing
disease.
2|Page
, Figure 4- An Illustration depicting Bacterial Budding
Occurring in both multicellular and unicellular, bacteria can also multiply through
budding. A small bud will start to form in the exterior of the microbe, become a daughter
cell and separate from the parental cell. Chronologically:
i. A protuberance/swelling emerges from the bacterial cell.
ii. DNA and cytoplasm in the bacterium divides, the bud will receive the
copies.
iii. The bud enlarges in size, evolving into a new cell, a daughter cell. The
daughter cell will separate from its parent cell.
iv. The budding will result in a chain of bacterial cells.
Bacterial Disease
Listeriosis is a foodborne disease attained when an individual intakes a substance that is
contaminated with a gram-positive bacterium known as Listeria Monocytogenes. The
highest instances of this condition where found when the diagnosed digested
cooked/cured meat, poultry, sea food products and pre-prepared sandwiches and salads.
Essentially almost all ready-to-eat products.
When the Listeria monocytogenes is ingested, the bacteria replicated in the liver,
traveling through the body via the bloodstream invading many places, such as the brain,
intestines and spinal cord.
Listeria monocytogenes has a multifactorial virulence system. For instance, its ability to
grow at temperatures as low as 0oC permits the multiplication/replication at typical
refrigeration temperatures, greatly increasing its ability to invade human food.
Additionally, it has a thiol-activated hemolysin, listeriolysin O, that has been identified in
paying a crucial role in the organisms’ ability to multiply and spread from cell to cell.
This bacterial infection can be compartmentalised into two groups (www.who.int):
i. Non-Invasive Listeriosis (Febrile Listerial Gastroententis)
Considered to be a mild form, it affects relatively healthy individuals. The
period between exposure to an infection and the appearance of the first
symptoms is short, only a few days.
Symptoms are inclusive to muscle pain, diarrhoea, headaches and fever.
ii. Invasive Listeriosis
Considered to be a more oppressive, this form affects high-risk individuals in
the general population., such as infants, the elderly, pregnant woman, people
undertaking treatment for aids, or organs transplants.
Symptoms are inclusive of muscle pain, meningitis, septicaemia, and fever.
3|Page
