8. Useful and Harmful Microbes

Explanation: when yeast gets enough food, as in a sugar solution, a small outgrowth called a bud appears on the parent cell. The nucleus divides and one part enters the bud. The bud grows and separates as a new yeast cell, or stays attached and forms a chain. Only one parent is involved, so this is asexual reproduction.

Explanation: fungi growing on food items such as pickles, murabba, jam, sauce and chutney use the nutrients in them and release poisonous chemicals into the food. These poisons made by fungi (myco = fungus) are called mycotoxins. Food with fungal growth becomes poisonous and must not be eaten.

Explanation: rhizobium bacteria live in the root nodules of leguminous plants such as beans, peas, groundnut and soyabean. They fix atmospheric nitrogen and supply nitrogenous compounds (nitrates, nitrites and amino acids) to the plant. Nitrogen is essential for making proteins, so beans and pulses are rich in proteins. In return, the bacteria get carbohydrates from the plant; this is symbiosis.

Chicken pox is caused by a virus. Pneumonia, diphtheria and cholera are caused by bacteria.

Clostridia are harmful microbes that spoil food and cause food poisoning, tetanus and gas gangrene. Lactobacilli, rhizobia and yeast are useful microbes.

Rubella (German measles) is a viral disease of humans. Root rot, rust and mosaic are diseases of plants.

• Cooked dal is rich in carbohydrates and proteins, and it is moist.
• Microbes such as bacteria and yeast from the air fall into it. In the warm temperature of summer they grow and multiply very quickly.
• While obtaining nutrition, they ferment the carbohydrates in the dal and produce gases such as carbon dioxide.
• The bubbles of gas collect on the surface as foam, and the dal turns sour and gives a bad smell. The dal is spoiled and should not be eaten.

• Clothes stored for a long time, especially in the damp rainy season, can be spoiled by fungi (mould) and by insects such as moths and silverfish.
• Naphthalene balls slowly sublime, that is, change directly into vapour, which fills the cupboard or box.
• This vapour is harmful to insects and prevents the growth of fungi.
• So naphthalene balls protect stored clothes from fungal growth, bad smell and insect damage.

Common fungal diseases of humans are ringworm, athlete’s foot, dandruff and fungal infections of the nails and skin.

Modes of infection:

• Direct contact with an infected person.
• Using the belongings of an infected person, such as clothes, towels, combs, caps and footwear.
• Fungal spores present in the air, soil and damp places settling on the skin.
• Moist, sweaty skin and wet clothes, which help the spores to germinate.
• Contact with infected pet animals.

Preventive measures:

• Maintain personal hygiene; bathe daily and keep the skin clean and dry, especially between the toes and in skin folds.
• Do not share towels, combs, clothes or footwear.
• Avoid contact with infected persons and their belongings.
• Wear clean, dry cotton clothes; wash clothes well and dry them in sunlight.
• Keep the house dry and well ventilated; do not allow dampness.
• Get the infection treated by a doctor early and complete the treatment.

Under India’s national immunisation programme, infants are given these vaccines:

• BCG — against tuberculosis (at birth).
• OPV / IPV — against polio (at birth and in the following months).
• Hepatitis B — against hepatitis B (at birth).
• Pentavalent vaccine (DPT + Hep B + Hib) — against diphtheria, pertussis (whooping cough), tetanus, hepatitis B and Haemophilus influenzae type b.
• Rotavirus vaccine — against severe diarrhoea.
• PCV — against pneumonia.
• MR / measles vaccine — against measles and rubella (around 9 months), followed by booster doses.

Why: an infant’s immunity is not fully developed, and these diseases can be very serious or even fatal in young children. A vaccine trains the body to make antibodies against a particular disease before the child is exposed to it, so the child becomes immune. Vaccinating all children also stops these diseases from spreading in society; this is how smallpox was eradicated and polio has been controlled.

1. The microbe (bacterium or virus) that causes the disease is identified and isolated.
2. It is grown in large numbers under controlled conditions in the laboratory — bacteria in nutrient media, and viruses in living cells such as cell cultures or chick embryos.
3. The microbes are then either killed (by heat or chemicals), weakened (attenuated) so that they cannot cause the disease, or only a part of the microbe or its inactivated toxin (toxoid) is used.
4. This material is purified, and stabilisers and preservatives are added.
5. The vaccine is tested thoroughly for safety and effectiveness, then packed and stored at the right low temperature.

When the vaccine is given, the body treats it as the real microbe and produces antibodies against it; this protects the person if the real disease-causing microbe enters later.

Antibiotics are carbon compounds obtained from some bacteria and fungi that destroy harmful micro-organisms, mainly bacteria, or stop their growth. They act in different ways:

• Some, like penicillin, damage the cell wall of the bacteria, so the bacteria burst and die.
• Some stop the bacteria from making the proteins they need.
• Some stop the bacteria from growing and multiplying.

When the number of disease-causing bacteria falls, the body’s own immune system easily destroys the rest, and the person recovers. Antibiotics do not act against viruses, so they are not useful for the common cold or influenza.

Not always. Some antibiotics, such as amoxicillin and tetracycline, are used for both humans and animals, but many are different, and even the same antibiotic is given in a different dose and form.

• Animals suffer from different diseases, caused by different bacteria, so the antibiotic effective against them may be different.
• The dose depends on body weight and species; a cow, a dog and a human need very different doses.
• Some medicines that are safe for humans are harmful to certain animals, and the reverse.
• Some antibiotics are kept only for humans, so that overuse in animals does not make bacteria resistant to them.

So antibiotics for humans and animals are prescribed separately, by a doctor and by a veterinary doctor.

• Vaccines are made from the pathogens themselves, so pure, correctly identified strains must be kept to produce the vaccine again and again, and to test its quality.
• Pathogens can change over time; stored samples help scientists compare new strains and update vaccines, as is done for influenza.
• They are also needed for research on the disease and its treatment.
• If they are not stored safely, they may escape and infect laboratory workers and the public, causing an epidemic. They could also be misused.

Hence they are stored under strict safety rules in specially built laboratories.

Antibiotics that are effective against a wide variety of bacteria are called broad-spectrum antibiotics. They are used when the symptoms of a disease are seen but the exact pathogen cannot be identified. Examples: ampicillin, amoxicillin, tetracycline.

The process in which micro-organisms such as bacteria and yeast break down carbohydrates (sugars), in the absence of oxygen, into simpler substances like alcohol, carbon dioxide or lactic acid, to obtain energy, is called fermentation. Examples: lactobacilli convert the lactose of milk into lactic acid to form yoghurt; yeast converts sugar into alcohol and carbon dioxide, which makes bread dough rise.

Carbon compounds obtained from some bacteria and fungi, which destroy harmful micro-organisms or prevent their growth, are called antibiotics. Example: penicillin, obtained from the fungus Penicillium.

Points you can use for the discussion:

• A generic medicine contains the same active ingredient, in the same strength and form, as a brand-name medicine, and works in the same way. It is sold under the name of the chemical (for example, paracetamol) rather than a brand name.
• Generic medicines are much cheaper, because the company does not spend on research, advertising and branding for them.
• In India, generic medicines are sold at low prices through Pradhan Mantri Bhartiya Janaushadhi Kendras.
• They must meet the same quality standards set by the drug-control authorities.
• Generic medicines should also be taken only on a doctor’s prescription; a patient can ask the doctor to prescribe by the generic name.