The word 'contamination' stands for mixing of unwanted constituent/s into the system; this unwanted entity also does not belong to that system and referred as 'contaminant'. Bacteria are potential contaminants of various systems like air, water, soil, food and fuels and responsible for undesirable to hazardous effects on these systems. Contaminant bacteria are also not the part of normal flora of air, water and soil.
Air: Since childhood, we are aware of airborne diseases like diphtheria, whooping cough, pneumonia, tuberculosis, leprosy and hay fever. The main bacterial agents of airborne diseases are streptococci, staphylococci, pneumococci, Legionella, Haemophilus, Klebsiella, Bordetella, Corynebacterium, Bacillus anthracis, tubercule and lepare bacilli. Pathogenic bacteria are introduced into the air by various terrestrial activities like dusting, sneezing, coughing and cleaning. The air of slaughter houses, sewage treatment plants, air conditioners, indoor theaters, railway stations, airports, offices, and ball room or conference halls is always contaminated by pathogenic bacteria. At such places there is guaranteed risk of transmission of bacterial infections. Bacteria thrive in air as droplet nuclei or aerosols. Droplet nuclei and aerosols are the dust particles infested with bacteria; eventually they are carried by winds from place to place and spread bacterial infection.
Water: Water is readily get contaminated via number of sources like domestic and industrial wastes, faecal matter, rain water carrying air bacteria, agricultural soils consisting manure residues, rubbish from different places and polluted river water. Marine water is also contaminated from industrial wastes and polluted rivers. Polluted or contaminated water is unpotable and contain human pathogenic bacteria. Salmonella, Vibrio, Shigella and coliform group of bacteria are causative agents of lethal diseases like typhoid, cholera, dysentery and gastroenteritis respectively in humans. Presence of coliforms is also used as indicator of water contamination.
Soil: Normal flora of soil gets contaminated by animal and human feces, sewage water and rain water which contain high population of pathogenic bacteria like coliforms, Clostridium, Salmonella and Vibrio. Soil also contains opportunistic plant pathogenic bacteria like Pseudomonas, Agrobacterium and Xanthomonas. Pathogens like clostridia persist in soil for long periods as sporulated bacteria. Soil contaminant bacteria are desiccation resistant and actively compete for soil nutrients with native bacterial population. Soil pathogenic bacteria are causative agents of water and food borne diseases of humans.
Food: Food is contaminated by pathogenic bacteria usually not following the hygienic practices during its preparation. Bacteria are introduced into food material via dirty hands, clothing, soil infested with fecal matter or use of contaminated water in the preparation. Ingestion of contaminated food causes food poisoning, which is indication of food contamination by bacterial pathogenic species of Clostridium, Micrococcus, Listeria, Lactococcus, Lactobacillus, Enterobacter, Shigella, Vibrio, Salmonella, Bacillus, Proteus, Campylobacter, Streptococcus and Staphylococcus. Bacteria are principle contaminants of foods like bakery, poultry, meat, fruits, vegetables, dairy products, juices and confectionaries.
Fuels: Since bacteria are capable of growing on any organic matter, they have not spared the fuels like diesel as carbon and energy source. Bacterial growth in diesel is presumed as serious contamination. Bacteria are introduced into diesel while filling of storage tanks and via air moisture. Contaminated diesel affects engine performance and occasional breakdown. Sulfate and iron reducing bacteria are major contaminants of diesel fuel.
Contamination of air is prevented by controlling personal habits. Mouth and nose should be covered when sneezing or coughing. It is the best precautionary measure to avoid formation of infected aerosols and disease transmission. Air conditioners and coolers should be cleaned and serviced, otherwise they provide fertile atmosphere for germination of bacteria. Water contaminating bacteria are removed by coagulation and filtration. They are killed by disinfection (chlorination), ozonation or UV irradiation. Waste water or treated waste, animal waste runoff should be disposed of properly. Sewage treatment plants or livestock should not be situated near water bodies. Water suppliers should be well covered and checked occasionally for presence of contaminants like coliforms. Once contaminated, it is never possible to completely decontaminate the soil. Therefore, like water precautions are taken to prevent soil from adulteration by feces or rainwater runoff. Proper hygienic conditions are maintained while processing or cooking the food. Food is spoiled by bacteria during long time storage even at freezing temperatures; therefore raw food (like meat) should be cleaned and refrigerated for only defined period for subsequent storage. To decontaminate diesel, bactericidal chemical have been used but the posed serious environmental and economical concerns. Filtration of diesel to remove water and bacterial growth has been ecofriendly method of choice.
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