EET 311

PUBLIC HEALTH MICROBIOLOGY

Introduction:
Public Health microbiology is a specialty which spans the fields of human, animal, food, water
and environmental microbiology, with a focus on human health and disease. It requires
laboratory scientists, epidemiologists, and clinicians to generate, integrate, analyze and
communicate epidemic intelligence. Public Health microbiology supports the monitoring of
known and emerging threats and facilitates the evaluation of effective interventions.
Pathogens
A pathogen is any organism that causes disease. Viruses, bacteria, fungi, and parasites are all
examples of pathogens.

Your body is naturally full of microbes. However, these microbes only cause a problem if your
immune system is weakened or if they manage to enter a normally sterile part of your body.

Pathogens are different and can cause disease upon entering the body.

All a pathogen needs to thrive and survive is a host. Once the pathogen sets itself up in a host’s
body, it manages to avoid the body’s immune responses and uses the body’s resources to
replicate before exiting and spreading to a new host.

Pathogens can be transmitted a few ways depending on the type. They can be spread through
skin contact, bodily fluids, airborne particles, contact with feces, and touching a surface touched
by an infected person.

Pathogen types

There are different types of pathogens, but we’re going to focus on the four most common types:
viruses, bacteria, fungi, and parasites.

Viruses
Viruses are made up of a piece of genetic code, such as DNA or RNA, and protected by a
coating of protein. Once you’re infected, viruses invade host cells within your body. They then
use the components of the host cell to replicate, producing more viruses.

After the replication cycle is complete, these new viruses are released from the host cell. This
usually damages or destroys the infected cells.

Some viruses can remain dormant for a time before multiplying again. When this happens, a
person appears to have recovered from the viral infection, but gets sick again.

Antibiotics do not kill viruses and therefore are ineffective as a treatment for viral infections.
Antiviral medications can sometimes be used, depending on the virus.

Bacteria

Bacteria are microorganisms made of a single cell. They are very diverse, have a variety of
shapes and features, and have the ability to live in just about any environment, including in and
on your body. Not all bacteria cause infections. Those that can are called pathogenic bacteria.

Your body can be more prone to bacterial infections when your immune system is compromised
by a virus. The disease state caused by a virus enables normally harmless bacteria to become
pathogenic.

Antibiotics are used to treat bacterial infections. Some strains of bacteria have become resistant
to antibiotics, making them difficult to treat. This can happen naturally, but also happens because
of the overuse of antibiotics, according to the World Health Organization (WHO)Trusted Source.

Fungi

There are millions of different fungal species on Earth. Just 300Trusted Source or so are known
to cause sickness. Fungi can be found just about everywhere in the environment, including
indoors, outdoors, and on human skin. They cause infection when they overgrow.
Fungi cells contain a nucleus and other components protected by a membrane and a thick cell
wall. Their structure can make them harder to kill.

Some new strains of fungal infections are proving to be especially dangerous, such as Candida
aurus, and have prompted more research into fungal infections.

Parasites

Parasites are organisms that behave like tiny animals, living in or on a host and feeding from or
at the expense of the host. Though parasitic infections are more common in tropical and
subtropical regions, they can occur anywhere.

Three main types of parasites can cause disease in humans. These include:

 protozoa, which are single-celled organisms that can live and multiply in your body

 helminths, which are larger, multi-celled organisms that can live inside or outside your
body and are commonly known as worms

 ectoparasites, which are multi-celled organisms that live on or feed off your skin,
including some insects, such as ticks and mosquitos

They can be spread several ways, including through contaminated soil, water, food, and blood, as
well as through sexual contact and via insect bites.

AIR-BORNE INFECTIONS

Airborne disease can spread when people with certain infections cough, sneeze, or talk, spewing
nasal and throat secretions into the air. Some viruses or bacteria take flight and hang in the air or
land on other people or surfaces.
When you breathe in airborne pathogenic organisms, they take up residence inside you. You can
also pick up germs when you touch a surface that harbors them, and then touch your own eyes,
nose, or mouth.

Because these diseases travel in the air, they’re hard to control. Keep reading to learn more about
the common types of airborne diseases and what you can do to protect yourself from catching
them.

Common air-borne diseases

Corona-virus/ Covid-19

A rapidly spreading coronavirus, SARS-CoV-2, and the disease it causes, COVID-19, has been
responsible for millions of infections and hundreds of thousands of deaths globally in 2020.
Information on coronavirus and COVID-19 is constantly being updated as a result.

While the coronavirus that causes COVID-19 is not generally considered to be airborne, there
may be some situationsTrusted Source in which the virus can act like an airborne disease. These
include certain clinical settings in which people are receiving intensive medical treatment. In
usual situations, SARS-CoV-2 is spread through respiratory droplets after a person coughs or
sneezes, but these droplets are larger than what is considered airborne.

The most common symptoms of COVID-19 include fever, cough, fatigue, and shortness of
breath. If you experience these symptoms, see a doctor immediately.

The common cold

MillionsTrusted Source of cases of the common cold occur each year in the United States. Most
adults get two or three colds a year. Children tend to get them more frequently.

The common cold is the top reason for absences at school and work. There are many viruses that
can cause a cold, but it’s usually a rhinovirus.
Influenza

Most of us have some experience with the flu. It spreads so easily because it’s contagious about a
day before you notice the first symptoms. It remains contagious for another 5 to 7 days. If you
have a weakened immune system for any reason, you can spread it to others longer than that.

There are many strains of the flu, and they are constantly changing. That makes it difficult for
your body to develop immunities.

Chicken pox

Chickenpox is caused by the varicella-zoster virus. If you have chickenpox, you can spread it for
a day or two before you get the telltale rash. It takes up to 21 days after exposure for the disease
to develop.

Most people get chickenpox only once, and then the virus goes dormant. Should the virus
reactivate later in life, you get a painful skin condition called shingles.

If you haven’t had chickenpox, you can contract it from someone with shingles.

MUMPS

Mumps is another very contagious viral disease. You can spread it before symptoms appear and
for up to 5 days after. Mumps used to be quite common in the United States, but rates
have declined by 99 percentTrusted Source due to vaccination.

From January 1 to January 25, 2020, 70 cases in the United States were reported to the CDC.
Outbreaks tend to occur in densely populated environments.

Measles
Measles is a very contagious disease, particularly in crowded conditions.

The virus that causes measles can remain active in the air or on surfaces for up to 2 hours.
You’re able to transmit it to others up to 4 days before and 4 days after the measles rash appears.

Most people get the measles only once.

Measles is a leading cause of death among children worldwide and was responsible for 140,000
deathsTrusted Source in 2018. It’s estimated that the measles vaccine prevented around 23
million deaths from 2000 to 2018.

The disease is less common in the United States and occurs mostly in people who haven’t been
vaccinated. There were 1,282 casesTrusted Source reported in 2019. As of March 2, 2020, there
have been 12 confirmed cases in 2020.

Whooping cough (pertussis)

This respiratory illness causes swelling of the airways that results in a persistent hacking cough.
It’s at the height of contagiousness for about 2 weeks after the coughing starts.

Worldwide, there are about 24.1 millionTrusted Source cases of whooping cough every year,
resulting in 160,700 deaths.

In 2018Trusted Source, there were 15,609 reported cases in the United States.

Tuberculosis (TB)

TB, also known as consumption, is an airborne disease. This is a bacterial infection that doesn’t
spread easily. You generally have to be in close contact with a person who has it for a long time.
You can contract TB without becoming ill or transmitting it to others.

About 1.4 billion people worldwide have TB. Most aren’t sick. About 10 million people
worldwide have active TB.

People with a weakened immune system have the greatest risk of developing the disease.
Symptoms can appear within days of exposure. For some, it takes months or years to activate.

When the disease is active, bacteria rapidly multiply and attack the lungs. It can spread through
your bloodstream and lymph nodes to other organs, bones, or skin.

Diphtheria

a serious infection of the nose and throat that’s easily preventable by vaccine

a sheet of thick, grey matter covers the back of the throat, making breathing difficult

Once a major cause of sickness and death in children, diphtheria is now rare in the United States.
Due to widespread vaccination, fewer than five cases have been reported in the past decade.

Worldwide, there were about 7,100 casesTrusted Source of diphtheria in 2016, but it may be
underreported.

The disease injures your respiratory system and can damage your heart, kidneys, and nerves

Control of air-borne diseases

Although it’s impossible to completely avoid airborne pathogens, there are some things you can
do to lower your chances of getting sick:
  Avoid close contact with people who have active symptoms of disease.

 Stay home when you’re sick. Don’t let vulnerable people come in close contact with you.

 If you must be around others, wear a face mask to prevent spreading or breathing in
germs.

 Cover your mouth when you cough or sneeze. Use a tissue or your elbow to cut down on
the possibility of transmitting germs on your hands.

 Wash your hands thoroughly (at least 20 seconds) and often, especially after sneezing or
coughing.

 Avoid touching your face or other people with unwashed hands.

Vaccines can reduce your chances of getting some airborne diseases. Vaccines also lower the
risk for others in the community. Airborne diseases that have vaccines include:

 chickenpox

 diphtheria

 influenza: vaccine updated every year to include strains most likely to spread in the
coming season

 measles: usually combined with vaccine for mumps and rubella, and is known as the
MMR vaccine

 mumps: MMR vaccine

 TB: not generally recommended in the United States

 whooping cough

In developing countries, mass immunization campaigns are helping to lower the transmission
rates of some of these airborne diseases.
 ROLE OF MICROBES IN MATERIAL DEGRADATION
Microbial degradation/biodegradation is defined as the biologically catalyzed reduction in
complexity of chemical compounds. Indeed, Microbial degradation is the process by which
organic substances are broken down into smaller compounds by living microbial organisms.
When biodegradation is complete, the process is called "mineralization". However, in most
cases the term biodegradation is generally used to describe almost any biologically mediated
change in a substrate.

1. FOOD
Food spoilage is a common concern for both consumers and the food industry. Have you ever
wondered why your favorite fruits go bad or why that leftover pasta in the fridge suddenly
develops an unpleasant odor? The answer often lies in the world of microbiology.

In this post, we delve into the role of microbiology in food spoilage, exploring its causes, effects,
and effective prevention methods.

Understanding Food Spoilage

What is Food Spoilage?
Food spoilage refers to the deterioration in the quality and safety of food products, making them
unsafe to consume. It is here, microorganisms play a pivotal role in facilitating the process.

Common Microorganisms Involved

There are several types of microorganisms which contribute to food spoilage, including bacteria,
yeast, and molds. They thrive in various environmental conditions and can rapidly multiply in
food.

How Microorganisms Cause Food Spoilage

Microbial Metabolism: Microorganisms metabolize food components, breaking them down into
simpler compounds. During this process, they produce byproducts that can alter the taste,
texture, and smell of the food.

Enzymatic Reactions: Microbes also produce enzymes that accelerate chemical reactions in
food. These enzymes can lead to the breakdown of proteins, fats, and carbohydrates, resulting in
undesirable changes in food quality.
Effects of Microbial Activity on Food
Microbial activity can cause food to become mushy, slimy, or grainy. For instance, the presence
of certain bacteria can soften vegetables and fruits. Microbes release compounds that generate
off-flavors and odors in food. These can range from sour or rancid notes to ammonia-like smells.

2. TEXTILES AND CORDAGE

Microbes play a significant role in the degradation of textiles and cordage, often contributing to
their breakdown through various mechanisms:
Biological Degradation: Microorganisms such as bacteria, fungi, and algae can colonize textile
and cordage materials, breaking down the fibers through enzymatic action. These organisms
secrete enzymes that degrade the organic components of textiles, including cellulose, lignin, and
proteins, leading to the weakening of the material structure.
Moisture and Temperature: Microbial degradation is often accelerated in environments with
high moisture and temperatures. Textiles and cordage used in outdoor settings or in humid
conditions are more prone to microbial attack. Moisture provides a medium for microbial
growth, while elevated temperatures can enhance microbial activity and enzyme production,
speeding up degradation.
Biofouling: In marine environments, textiles and cordage are susceptible to biofouling, where
microorganisms attach and form biofilms on the material surface. These biofilms can trap debris
and moisture, creating an ideal environment for further microbial growth and degradation.
Chemical Changes: Microbial activity can also lead to chemical changes in textiles and cordage,
such as acidification or alkalinization of the surrounding environment. These chemical changes
can further contribute to the degradation of materials by altering their pH levels and promoting
the breakdown of fibers.
3. RUBBER
Rubber is an essential part of our daily lives with thousands of rubber-based products being made
and used. Natural rubber undergoes chemical processes and structural modifications, while
synthetic rubber, mainly synthetized from petroleum by-products are difficult to degrade safely
and sustainably. The most prominent group of biological rubber degraders are Actinobacteria.
Rubber degrading Actinobacteria contain rubber degrading genes or rubber oxygenase known as
latex clearing protein (lcp).
All rubber-degrading isolates were identified as members of the actinomycetes, a large group of
mycelium-forming Gram-positive bacteria.
4. Petroleum products
Oil or petroleum degradation is an effective environmental bioremediation technique in which
micro-organisms digest petrochemical pollutants.
oil degradation, the idea is that hydrocarbon molecules will be broken down into smaller
constituents. These constituents will then either be removed or absorbed into the natural
environment in a safe – or at least safer – fashion.

Bioremediation Certain portions of oil are biodegradable and as such, proper application of
certain fertilizers can speed up this process as much as tenfold. Certain plants
and their associated microorganisms have also shown promise in speeding up
the breakdown of oil. However, even an amplified biodegradation process (Fig.
6) takes weeks, or even years, and, as such; it is commonly used in conjunction
with other cleanup activities.

SOME MICROORGANISMS THAT DEGRADE PETROLEUM PRODUCTS

The number of different types of bacterium and microorganism suitable for deployment in
removing oil spills and related waste may be greater than many had realised. There are at least 79
types of bacteria that can be used to digest and remove petroleum hydrocarbons, and the number
may be substantially greater than this.
Bioremediation bacteria examples include:
 Pseudomonas aeruginosa
 Mycobacterium cosmeticum
 Aeribacillus pallidus
 Achromobacter xylosoxidans
 Bacillus licheniformis
 Bacillus mojavensis
 Pseudomonas sp.
 Alcanivora xsp.
 Oleispira antarctica
 Gordonia sihwensis
 Bacillus sp.
 Tavassoli
 Citrobacter sp.
 Enterobacter sp.
 Staphylococcus sp.
 Lysinibacillus sp.
MICROORGANISM DEGRADATION IN THE CONTEXT OF HYDROCARBONS
In most cases, the bacteria are seeking a source of carbon to use as a fuel for growth and
reproduction. Hydrocarbon molecules, such as those found in oil, are rich in carbon, but these
carbon atoms are bonded together, either in chains or in aromatic benzene rings.
The types of bacteria listed above are able to break the molecular bonds and release the carbon.
This carbon is then digested directly by the bacterium while other atoms and molecules are
released. In most cases, these released atoms and molecules – generally hydrogen and
surplus carbon atoms from within the degraded hydrocarbon – are easier for the local ecosystem
to deal with and do not pose the same sort of threat as that of the full hydrocarbon molecule.
Alternatively, microorganism bioremediation can be deployed alongside another environmental
remediation technique to maximize its efficacy.
DIRECT AND INDIRECT BIODEGRADATION
The degradation of oil and hydrocarbons can occur in two different ways. On the one hand, there
is direct action, where the microorganism targets the carbon within the molecule and uses this as
a direct source of fuel. In other words, the microorganism is directly breaking the molecule down
to release the carbon it contains.
On the other hand, there is indirect action. This is where degradation occurs due to a byproduct
of the microorganism’s chemical and biological reaction. When the microorganism metabolizes a
fuel source, it may release additional chemicals as a result. These chemicals may also break
down the hydrocarbon or interact with the molecule in another way.
Direct action tends to be the most effective in breaking down the hydrocarbon. The byproduct
may only provide limited degradation capability and so may not be of much use by itself.
However, this byproduct only appears following the metabolization process, which means direct
and indirect forms of biodegradation generally work side by side. The most effective forms of
bacteria in the oil degradation process are those that directly target the carbon stored in the
molecule and produce a metabolic byproduct that enhances the degradation capabilities.

PRINCIPLES IN PREVENTION OF MICROBIOLOGICAL DETERIORTION:

Control of micro-organisms means reduction in the number and/or activity of micro-organisms.

The main objectives behind the microbial control include :
1. Prevention of occurrence and transmission of diseases and infection.
2. Prevention of cotamination or growth of undesirable organisms, especially during
microbiological studies, fermentation processes, analytical methods or processes involving use of
microorganisms.
3. Prevention and control of deterioration of materials or spoilage foods of by micro-organisms.
Principles of microbial control :
Control of micro-organisms can be achieved by meeting with any of the following criteria.
1. Killing of micro-organisms.
2. Removal of micro-organisms.
3. Inhibition of the growth and activities of micro-organisms.
The agents capable of killing the micro-organisms or Inhibiting their growth and activity are
called antimicrobial agents.

FOOD PRESERVATION METHODS

Freezing
Freezing conditions inhibit bacteria growth. So, storing food properly in the freezer can make it
last for a long time. Years, in fact. That said, frozen emergency pizza from 2020 should probably
be thrown out now.

To optimise your freezer to preserve food, ensure it’s set at the right temperature. Freezers
should be set between -18°C and -22°C. Fresh, unpacked or pre-cooked foods should be stored in
freezer bags or airtight containers before being put in the freezer.

Don’t freeze food after its use-by or best-before date. If its use-by has passed and you haven’t
frozen it yet, bin it. And if you’ve missed the best-before date, eat it sooner rather than later.

Frozen food must be defrosted before it can be eaten. Packaged food will come with some
guidance on how long it needs to thoroughly defrost. Once defrosted, you can’t refreeze it
because bacteria can grow while the food item is thawing.

Salting
Salting is excellent for drawing water out of certain foods. This, like sugaring, stops bacteria
from growing. Wet curing is when salt is mixed with water and sometimes sugar. Food is added
to this mixture and placed in cans. Dry curing is where salt is put directly onto foods like meat.
This draws out water.

Canning

This method of food preservation removes oxygen from foods. The food stored in an airtight,
acidic, high salt or sugar environment prevents bacteria from growing.

Canned food must be handled hygienically and be of good quality. Jars should be specifically
designed for canning. This is to ensure that they will be airtight.

You need to be careful with this particular food preservation method, though. This is because the
C. botulinum bacteria thrive in environments absent of oxygen. Suppose the canning process you
use hasn’t been successfully tried and tested. In that case, this bacterium can start to grow and
produce toxins. These toxins can lead to botulism poisoning, a rare but life-threatening condition.

Air drying, smoking