Microbiology
assignment 2b
Fiona
Noonan 21/08/09
Define
bacteria, fungi, algae, protozoan, helminths and viruses
Bacteria-
These are single celled organisms which are essential to all life and live
either independently or as a parasite. Bacteria have three basic shapes which
include bacillus, coccus and spiral. Bacteria multiply through cell division
and in most cases can be killed by antibiotics. (Medicine Net 2009, Swan TAFE 2009)
Fungi-
Fungi is a general term which is used to describe a group of eukaryotic
protists which are characterized by the absence of chlorophyll and by the
presence of a rigid cell wall. Fungi can exist as single celled yeasts or as
larger multicellular moulds and are classified according to the type of sexual
spore they form. Most fungi are decomposers and are commonly found to cause
disease in immune suppressed individuals. Fungi can spread either through
direct contact, or it can be airborne.
(Biology online 2007 Swan TAFE 2009),
Algae- Algae
can be multi or unicellular, however it is only the unicellular species which
can cause disease. All algae reproduce asexually and are abundant in fresh,
salt water, soil and attached to some plants. Algae are photosynthetic and have
an important role in the balance of nature. In terms of disease, algae are food
borne or water borne.
(Swan
TAFE 2009),
Protozoans- These
are unicellular eukaryotes which live independently or as parasites and can
move by the use of pseudopods, cilia and flagella. Protozoa are mostly found in
soil or water and many can make up the normal flora of larger animals. Protozoa
reproduce asexually and have many shapes. The pathogenic spread of protozoa
includes vectors, food borne or direct contact. (John Heritage 2006, Swan TAFE 2009)
Helminths –
These are not strictly micro-organisms as many are multicellular eukaryotes.
Helminths can be classified into three classes – nematodes, cestodes and
trematodes. Helminths often have complex life cycles, with at least one part
living in its main host where it can achieve sexual maturity and reproduce. Its
host can be animals, or humans and can be food borne, vector borne or can
spread through direct contact.
(John Heritage 2006, Swan TAFE 2009)
Viruses –
Viruses are the simplest of microbiological entities and are comprised only of
a nucleic acid core (DNA or RNA), wrapped in a protein coat. Viruses are extremely
small and the use of an electron microscope is needed to view them. Viruses are
acellular and need a host cell to enter in order to reproduce by means of
taking over the cells reproductive material. Because viruses live in a host
cell they are immune to the use of anti-biotics and can be spread in many ways
including direct contact or air borne.
(Swan
TAFE 2009, John Heritage 2006)
List
some important diseases associated with each of these micro-organisms
Bacteria
– Bacterial
infection is among the most common types of disease in humans. The disease
caused by bacteria are so vast they can range from food poisoning to some types
of cancer. Even though some bacteria kill a high percentage of the people
infected, bacterial infections do not kill all of there victims.
Vibrio
cholerae is the bacteria responsible got the cause of cholera,
which has caused many epidemics and even pandemics. Transmission to humans is
by contaminated water or food.
Legionella
pneumoniae is the bacteria which causes Legionnaire’s disease which
is a life threatening respiratory disease. It survives in moist places like air
conditioners or hot-water pipes and is air borne. (Dr. T. M. Wassenaar 2009)
Fungi –
Fungi cause a wide variety of diseases in humans, some much more serious than
others.
Cryptococcus
neoformans is a disease of the lungs and spinal cord which is
serious in people with AIDS, or other immune suppressed individuals. This bacteria
is mostly spread by dust in the air.
Candida albicans is another human pathogen caused
by Fungi. This organism causes disease of the oral cavity (thrush), as well as
yeast diseases in the vagina. Normal flora usually keeps the growth of Candida
albicans
under control. (Cliffs Notes 2009)
Algae -
There are only a few species of algae which are known pathogens in humans, as
most pathogenic varieties only affect other plants or aquatic animals.
Protothecosis is a disease
caused by a species if of green algae called Prototheca wickerhami. It is a rare infection that usually only
affects humans and other mammals living in tropical climates. The source of
infection is often unknown but can be related to a penetrating injury in come
cases. This species of algae lacks chlorophyll.
Certain marine
dinoflagellates of the genera Gonyaulax and Gymnodinium produce poisonous
substances which are very harmful to fish or other animals who may consume it,
even humans. They are responsible for the red tide, and cause death to aquatic
animals or to people who consume contaminated shellfish. The toxins produces by
such algae are extracellular, or can be set loose by bacterial decomposition.
Some species of blue-green
algae of the genera Anabaena and Microcystis also produce toxins that poison
sea water which are harmful to birds and mammals which drink the poisoned
water. (Edward Villablanca 2009,Dr S. Roy 2009)
Protozoan –
Several species of protozoans infect humans and inhabit the body as commensals
or parasites. The parasitic protozoans of major medical importance include
species of amoebae, flagellates and sporozoans.
Entamoeba
histolytica is protozoan which inhabits the large
intestine. It is mostly harmless, but can result in the disease amebiasis,
where is has penetrated the mucous membrane of the intestine and multiplied.
Once it has multiplied it can get into the bloodstream and establish secondary
sites of infection. People usually acquire this disease from drinking water or
food contaminated with human feces.
Giardia
lamblia is the worlds most common cause of water-borne diarrhea.
Giadiasis outbreaks are common in enclosed communities (schools, hospitals,
prisons). Giardia attaches to the surface of the large intestine, where in
numbers, can affect nutrient absorption causing excessive gas production,
cramps and diarrhea. (K.S.Saladin 2008)
Helminths
– There
can be over 100 different types of parasitic worms living in human bodies.
Helminths invade a persons body mostly through food or water and are
responsible for many health problems because they secrete toxins and can steal
vital nutrients from the food we eat.
Enterobius vermicularis causes threadworm infection and is thought to be
the most common worm parasite in children.
Taenia
saginata are the most common cause of human tapeworm. Most
tapeworm infections go unnoticed, however, if left unchecked the eggs can enter
the blood stream and enter muscle tissue and organs causing cysts. (John
Heritage 2006)
Viruses
– viruses
can often lead to very serious or even deadly diseases and have a multitude of
symptoms. Viruses are in our environment all the time and enter our bodies
through openings such as mouth, nose or breaks in the skin where they can find
a host cell to infect.
human papilloma virus(HPV) is a group of over 100 related viruses that
causes warts or papillomas which are mostly non-canercous tumors which grown on
body surfaces. The papilloma viruses are attracted to and are
able to live only in squamous epithelial cells in the body. Some strains of
genital HPV have been linked with cancer in both men and women. (American
Cancer Society 2009)
Herpes simplex virus
1 and 2( HHV-1 and HHV-2)
are two species of the herpes virus family which cause infections in humans. Herpes
simplex may cause life-long infections and produce watery blisters most
commonly on the mouth or genitals.
(NHS choices2009)
Discuss
factors that determine infection including virulence and pathogenicity
There are many factors which
contribute to what an individual’s response will be to a given antigen.
Pathogenicity is
the ability of a microbe to cause disease. Some microbes always cause disease,
while others only cause disease under the right circumstances. Some microbes
which live in the human gut for example only become pathogenic once they enter
the blood stream, however in normal circumstances they do not cause disease. On
the other hand, the human flu viruses almost always cause disease.
Virulence is
another factor which determines infection and refers to the degree of how
pathogenic an organism is. A virulent organism is one that usually produces a
severe disease which can lead to death. For example HIV would be considered
virulent because the disease it causes is severe and leads to death, in
contrast with the common cold; though almost always pathogenic are not for the
most part deadly.
Resistance
and susceptibility is a massive factor in determining infection.
Resistance is the ability of a host to ward off disease through non-specific
and specific defenses, susceptibility is the lack of resistance to a disease.
Our immune system protects us
from most foreign macromolecules or invading organisms. Non specific resistance
is our defense to any pathogen regardless of species and includes such things
as skin, mucous and inflammation. Specific resistance can be referred to as
acquired immunity as it develops in the body as a result of the formation of
antibodies in response to antigens. Humans gain immunity against diseases
through exposure to the specific antigen.
Without these forms of
resistances humans would not have any defense against disease and would always
be sick. In AIDS patients there immune system (resistance) is affected making
them much more susceptible to invading pathogens. (Swan TAFE 2009)
Draw
a table or chart showing the chain of infection for three different pathogens
|
Infectious
Agent |
Staphylococcus
aureus (Golden staph) |
Measles Virus (Measles) |
Mycobacterium
tuberculosis (Tuberculosis) |
|
Reservoir |
Skin and Nose of colonized individuals.
Skin of some animals (dogs, cats, cows, poultry & pigs) |
Humans who are infected
with the disease |
Infected Humans |
|
Portal
of Exit |
Direct contact or environmental
surfaces |
Coughing, sneezing, direct
contact, urine |
Coughing, sneezing, spit, direct
contact |
|
Mode
of transmission |
Direct contact (hands,
infection site and contaminated surfaces.) |
Airborne, direct contact or
environmental surfaces, droplets |
Airborne, direct contact or
environmental surfaces |
|
Portal
of Entry |
Broken skin or body
orifices |
Inhaled – lungs, or comes
into contact with mucous membrane on the host |
Inhaled – lungs or comes
into contact with mucous membrane on the host |
|
Susceptible
Host |
Anyone more likely if in
crowded living conditions, lack of cleanliness, frequent skin contact, lack
of healthcare or overuse of anti-biotics. |
Anyone, malnourished
children or people with reduced immunity, people who are not vaccinated. |
People who are not vaccinated,
people with reduced immunity, communities where it is common. |
Tacoma Health Department 2006,
World Health Organization 2009, K. Todar 2009
Describe
body defenses in response to infection
The response to infection in
the human body is great. We have many ways to protect, and fight against
pathogens. These can be broken down into non-specific and specific body
defenses.
Non specific defenses are
defenses which we a born with and defend against any pathogen regardless of
species. Non specific defenses can be further broken down into first and second
line defenses.
Non specific first line
defenses include skin, mucous membranes, body secretions and normal flora. Skin is one of the largest organs of
the body and when intact provides the first line of defense against diseases.
The cells of the skin are closely packed together in layers and on there
surface, the dead cells contain keratin protein. This provides a barrier which
most pathogens cannot penetrate unless broken.
Some of our body surfaces do
not have skin, for example our respiratory tract. Instead, these surfaces which
come into contact with the outside world have a mucous membrane which, like skin, inhibits the penetration of many
microbes. Mucous membranes as the name suggests also secrete mucous which not
only prevents the tracts from drying out, but also trap microbes which may be
on the surface.
Both skin and mucous
membranes are physical barriers. Other barriers can be referred to as mechanical barriers. Mechanical
barriers include the lacrimal apparatus which manufactures and drains away
tears, saliva which dilutes and washes away microbes into the stomach, cilia
which traps microbes and the epiglottis which is tissue that covers the airways
during swallowing.
To prevent disease, our
bodies also have chemical barriers
which are body secretions that inhibit the growth of, or kill pathogens. Sebum
while not only prevents hair from drying out, also forms a protective film over
the skin. Due to its composition of fatty acids, sebum inhibits the growth of
some species of bacteria and fungi. Perspiration is produced by sweat glands which
flushes out microbes from the skin and also breaks down the cell walls of some
bacteria. In our stomachs gastric juice is produced which is of extremely high
acidity. The acidity kills most bacteria who enter our digestive system. Due to
its pH, vaginal secretions also work in a similar way to the stomach in
killing, or inhibiting overgrowth of microbes. In our blood there are
tranferrins which reduce the amount of available iron, inhibiting the growth of
microbes.
Chemical barriers also
include interferons and the compliment
system. Interferons are proteins produced by cells infected by viruses and
by T cells. Interferons cannot stop viruses from entering the cell but they can
stop it from reproducing and hence the virus cannot attack new cells. The
compliment system is a group of more than 20 plasma proteins that circulate in
the blood in a dormant state until they are activated. They are needed in the
distruction of cellular antigens by breaking down their cell membranes and the
labeling of noncellular antigens. Some stimulate the release of histamine in
inflammation and others attract WBCs to the site.
Normal
flora this is another non specific first line of defense
helping to keep harmful microbes at bay. Normal flora are helpful microbes that
prevents the overgrowth of pathogens by competing with them for nutrients and
producing harmful substances which alter the environment such as the
availability of oxygen, and pH.
Non specific second line
defenses include inflammation and
phagocytosis. The main cause of inflammation is to try to contain the
damage, keep the pathogen from spreading, eliminate the cause and permit repair
to the damaged tissues. When cells are damaged histamine, kinins and
prostagladins increase the permeability of blood vessels causing inflammation. Blot
clots form around an abscess to prevent dispersion of the infection. This
process is beneficial as it destroys the pathogen if possible or removes it and
the by products from the body. Phagocytosis is the engulfing of a microbe by
cells known as phagocytes preventing it from causing it infection elsewhere in
the body.
A common response to
bacterial or viral infection is fever,
where the body exceeds normal temperatures. Bacterial endotoxins and
interleukin stimulate the hypothalamus and cause it to release prostogladins
which reset the hypothalamic thermostat of the body. Fever also increases the
bodies natural reactions to help restore damaged cells and tissues.
Once a pathogen has already
entered our body, specific immunity
can be needed to destroy it. Specific immunity is the ability of the body to
attack specific foreign organisms or substances. Antigens are anything that
trigger a specific immune response and are usually proteins or large
polysaccharides that make up part of the invading microbe. Such things as
pollen and egg whites are non-microbial antigens.
Immune responses involve the
production of proteins called antibodies
and lyphocytes. The majority of lyphocytes are T cells and B cells. In an
embryo the T cells are produced in the bone marrow and mature in the thymus. After
they have matured in the thymus the T cells move to the spleen, lymph nodes and
lymph nodules where they are found after birth. B cells are produced in
embryonic bone marrow and migrate directly to the spleen, lymph nodes and
nodules. They do not need to mature in the thymus.
When activated some B cells will divide and become plasma
cells that produce antibodies. Antibodies are formed against specific areas on
the antigen’s surface called antigenic determinants and have at least two
identical antigen binding sites. Once an antibody has bonded with an antigen,
it renders it harmless. When a cell is infected by an antigen, it presents an
abnormal antigen on its surface that T
cells can identify. Once a T cell identifies an infected cell it kills it
in order to prevent the infection of nearby cells.
(V.C. Scanlon, T. Sanders
2007, Swan TAFE 2009)
References
American
Cancer Society 2009, Human Papilloma Virus (HPV), Cancer, and HPV Vaccines –
Frequently Asked Questions, American Cancer Society
http://www.cancer.org/docroot/CRI/content/CRI_2_6x_FAQ_HPV_Vaccines.asp
Date
retrieved: 21/08/09
Biology
online 2007, Fungus, http://www.biology-online.org/dictionary/Fungus
Date
retrieved: 21/08/09
Cliffs
Notes 2009, Fungal Disease, Wiley Publishing
http://www.cliffsnotes.com/WileyCDA/CliffsReviewTopic/Fungal-Disease.topicArticleId-8741,articleId-8667.html
, Date retrieved: 21/08/09
Dr
S. Roy 2009, Protothecosis,
Histopathology-india.net
http://www.histopathology-india.net/Proto.htm
Date
retrieved: 21/08/09
Dr.
T. M. Wassenaar 2009, Pathogenic bacteria, The Virtual Museum of
Bacteria
http://www.bacteriamuseum.org/cms/Pathogenic-Bacteria/pathogenic-bacteria.html
Date
retrieved: 21/08/09
Edward
Villablanca 2009, Algae as Pathogens: the Bad Side of Algae,Associated
Content
http://www.associatedcontent.com/article/1339477/algae_as_pathogens_the_bad_side_of.html?cat=58,
Date retrieved: 21/08/09
John
Heritage 2006, Medical Microbiology – A Brief Introduction,
http://www.bmb.leeds.ac.uk/mbiology/ug/ugteach/icu8/introduction/protozoa.html
Date
retrieved: 21/08/09
K.S.Saladin
2008, Protozoan Diseases, Advameg Inc
http://www.biologyreference.com/Po-Re/Protozoan-Diseases.html
Date
retrieved: 21/08/09
K.
Todar 2009, Mycobacterium tuberculosis, Textbook of Bacteriology
http://www.textbookofbacteriology.net/tuberculosis.html
Date
retrieved: 21/08/09
Medicine
Net 2009, Bacteria,
http://www.medterms.com/script/main/art.asp?articlekey=13954
Date
retrieved: 21/08/09
NHS
choices2009, Herpes simplex virus, NHS choices
http://www.nhs.uk/Conditions/Herpes-simplex-virus/Pages/Introduction.aspx?r=1&rtitle=Herpes+simplex+virus+-+Introduction
Date
retrieved: 21/08/09
Swan TAFE (2009), Microbiology
Lecture Notes ,Swan TAFE Printing Service, WA
Tacoma
Health Department 2006
How
to Break the Chain of Infection in out Outpatient Clinic/Medical Office
Tacoma
Health Department, http://www.tpchd.org/files/library/66afed3797c40cba.pdf
Date
retrieved: 21/08/09
V.C.
Scanlon, T. Sanders 2007, Essentials of Anatomy and Physiology, F.A.
Davis Company
World
Health Organization 2009, Measles, WHO
http://www.who.int/topics/measles/en/
Date
retrieved: 21/08/09
