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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


Mycobacterium tuberculosis (Tuberculosis)


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)








American Cancer Society 2009, Human Papilloma Virus (HPV), Cancer, and HPV Vaccines – Frequently Asked Questions, American Cancer Society

Date retrieved: 21/08/09


Biology online 2007, Fungus,

Date retrieved: 21/08/09


Cliffs Notes 2009, Fungal Disease, Wiley Publishing,articleId-8667.html , Date retrieved: 21/08/09


Dr S. Roy  2009, Protothecosis,

Date retrieved: 21/08/09


Dr. T. M. Wassenaar 2009, Pathogenic bacteria, The Virtual Museum of Bacteria

Date retrieved: 21/08/09


Edward Villablanca 2009, Algae as Pathogens: the Bad Side of Algae,Associated Content, Date retrieved: 21/08/09


John Heritage 2006, Medical Microbiology – A Brief Introduction, University of Leeds Faculty of Biological Sciences UK

Date retrieved: 21/08/09


K.S.Saladin 2008, Protozoan Diseases, Advameg Inc

Date retrieved: 21/08/09


K. Todar 2009, Mycobacterium tuberculosis, Textbook of Bacteriology

Date retrieved: 21/08/09


Medicine Net 2009, Bacteria,

Date retrieved: 21/08/09


NHS choices2009, Herpes simplex virus, NHS choices

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,

Date retrieved: 21/08/09


V.C. Scanlon, T. Sanders 2007, Essentials of Anatomy and Physiology, F.A. Davis Company USA


World Health Organization 2009, Measles, WHO

Date retrieved: 21/08/09