Harmful Microorganisms

Microorganisms are useful as well as harmful also, 

1. Some microorganisms are pathogens which cause diseases to human animals and plants.

2. Bacteria and fungi  cause food spoilage and make them unfit for eating.

3 Bacteria cause diseases like cholera, typhoid, and diarrhea through water and food. Viruses can causes smallpox, cold, hepatitis polio and soon. Fungi and protozoa also cause diseases

5. Some microorganisms show antibiotic resistance to certain diseases.

6. Some microorganisms spoil food, clothing and leather.

Disease causing Microorganisms in Humans

Pathogens enter our body through the air we breathe, the water we drink or the food we eat. They can also get transmitted by direct contact with an infected person or carried through an animal. Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases. Examples of such diseases include cholera, common cold, chicken pox and tuberculosis. When a person suffering from common cold sneezes, fine droplets of moisture carrying thousands of viruses are spread in the air. The virus may enter the body of a healthy person while breathing. 

There are some insects and animals which act as carriers of disease causing microbes. Housefly is one such carrier. The flies sit on the garbage and animal excreta. Pathogens stick to their bodies. When these flies sit on uncovered food they may transfer the pathogens. Whoever eats the contaminated food is likely to get sick. So, it is advisable to always keep food covered. Avoid consuming uncovered items of food.

Another example of a carrier is the female Anopheles mosquito, which carries Plasmodium, the parasite of malaria. Female Aedes mosquito acts as carrier of dengue virus. All mosquitoes breed in water. By keeping the surroundings clean and dry we can prevent mosquitoes from breeding. To prevent the spread of communicable diseases keep a distance from infected persons and use a handkerchief on the nose and mouth while sneezing. 

Some of the common diseases affecting humans, their mode of transmission and few general methods of prevention are shown in Table

 

Human Disease	Causative Microorganism	Mode of Transmission	Preventive Measures
Tuberculosis   Measles Chicken Pox Polio	Bacteria- Mycobacterium tuberculosis Virus Virus  Virus	Air   Air Air/Contact  Air/Water	Keep the patient in complete isolation. Keep the personal belongings of the patient away from those of the others. Vaccination to be given at suitable age.
Cholera   Typhoid	Bacteria- Vibrio cholerae Bacteria- Salmonella typhi	Water/Food Water	Maintain personal hygiene and good sanitary habits. Consume properly cooked food and boiled drinking water. Vaccination.
Hepatitis A  Polio	Virus  Virus	Water Water	Drink boiled drinking water. Vaccination.
Malaria	Protozoa- Plasmodium	Mosquito	Use mosquito net and repellents. Spray insecticides and control breeding of mosquitoes by not allowing water to collect in the surroundings.

 

Disease causing Microorganisms in Animals

Several microorganisms cause diseases in plants and animals. For example, anthrax is a dangerous human and cattle disease caused by Bacillus anthracis. Foot and mouth disease of cattle is caused by a virus. Diseases in plants like wheat, rice, potato, sugarcane, orange, apple and others reduce their yield. They can be controlled by the use of certain chemicals which kill the microbes. 

Disease causing Microorganisms in Plants

Microorganisms cause disease in plants also. Citrus canker is caused by bacteria called Xanthomonas citri and spreads through air. Rust of Wheat is caused by Fungi called Puccinia triticina and spreads through air or Seeds. The Yellow Vein Mosaic of Okra (lady’s finger) is caused by Virus and spreads through Insects- Bhendi yellow vein mosaic virus cause this disease.

Food Poisoning

Make the food poisonous causing serious illness and even death. So, it is very important that we preserve food to prevent it from being spoilt.

Food Spoilage Microorganisms spoil our food. The bread left unused under moist conditions is attacked by fungus (Bread mould-Rhizopus). Spoiled food emits bad smell and has a bad taste and colour change.

Food poisoning could be due to the consumption of food spoilt by some microorganisms. Microorganisms that grow on our food sometimes produce toxic substances.

Microbes Cause Decomposition

Microbes are the agents of  decomposition of clothing and sheltering materials. They degrade foods and grains stored in granaries, supermarket or refrigerator, as well as natural structural materials and textiles used for our shelters and clothing.  Fungi and bacteria are the major microbial agents of decomposition in aerobic environments. Bacteria take over in environments that lack oxygen.

Microbial Corrosion

Microbial corrosion, also called microbiologically influenced corrosion (MIC), microbially induced corrosion (MIC) or biocorrosion, is "corrosion affected by the presence or activity of microorganisms in biofilms on the surface of the corroding material."  Some sulfate-reducing bacteria (anaerobic bacteria), like Desulfovibrio cause corrosion by producing hydrogen sulfide, Thiobacillus/Acidithiobacillus  produce sulfuric acid, Ferrobacillus directly oxidizes iron to iron oxides and iron hydroxides. Other bacteria produce various acids, or ammonia.