Which one of the following statements about microbes is not correct ?
- (a)They are used in sewage treatment plants.
- (b)They are used in industrial fermenters for the production of beverages.
- (c)No antibiotic has been obtained from any microbe.
- (d)They are used to get many bioactive molecules for the treatment of diseases.
Correct — C, No antibiotic has been obtained from any microbe. This statement is false, and spectacularly so — nearly every antibiotic in clinical use began life as a microbial product. Penicillin came from the mould Penicillium notatum, noticed by Alexander Fleming in 1928 when it killed the staphylococci growing on a contaminated plate, and turned into a usable drug by Howard Florey and Ernst Chain. Streptomycin came from the soil bacterium Streptomyces griseus, and the genus Streptomyces alone has given the world a large share of its antibiotics, including tetracycline, chloramphenicol and erythromycin. Antibiotics are, by their original definition, substances one microbe makes to inhibit another.
- (a)They are used in sewage treatment plants. — True, so it cannot be the answer. Secondary treatment in a sewage works is entirely microbial — aerobic flocs of bacteria and fungi digest the organic matter in the aeration tank, and anaerobic digestion of the settled sludge produces biogas.
- (b)They are used in industrial fermenters for the production of beverages. — Also true. Saccharomyces cerevisiae, brewer's and baker's yeast, ferments sugars to ethanol and carbon dioxide, and industrial fermenters of thousands of litres are standard equipment in the brewing and distilling industries.
- (d)They are used to get many bioactive molecules for the treatment of diseases. — True as well. Beyond antibiotics, microbes supply the cholesterol-lowering statins from Monascus and Penicillium species, the immunosuppressant cyclosporin from the fungus Tolypocladium, and the clot-dissolving streptokinase from Streptococcus.
Microbial biotechnology rests on the fact that microbes carry out chemistry we find useful and can be grown cheaply in bulk. The same organisms clean our waste water, ferment our food and drink, and manufacture medicines. In a fermenter the microbe is given the conditions it likes and the product is harvested from the broth; the vessel may hold a few litres in a laboratory or many thousands in a factory.
In a 'which is not correct' item, an absolute word is usually the giveaway. Statement (c) says 'no antibiotic has been obtained from any microbe', and a single counter-example destroys it. Penicillin is that counter-example and every student knows it, which is what makes this the easiest of the four to judge. Keep two related facts straight. Antibiotics act on bacteria and not on viruses, because viruses have none of the metabolic machinery the drugs attack. And the misuse of antibiotics selects for resistant strains, which is why courses must be completed and why their routine use in livestock is now discouraged.
- Penicillin was discovered by Alexander Fleming in 1928 from the mould Penicillium notatum, and developed for use by Florey and Chain.
- Streptomycin was obtained from the soil bacterium Streptomyces griseus, a genus that has yielded many antibiotics.
- Secondary sewage treatment relies on microbial digestion, and anaerobic sludge digestion yields biogas.
- Saccharomyces cerevisiae ferments sugars to ethanol and carbon dioxide in brewing and baking.
- Statins, cyclosporin and streptokinase are further medicines of microbial origin.
- Missing that an absolute statement such as 'no antibiotic from any microbe' needs only one counter-example.
- Believing antibiotics cure viral infections such as the common cold or influenza.
- Thinking of microbes only as agents of disease; most industrial uses are beneficial.
NDA writes three textbook-true statements and one sweeping negative, so scan first for the option that claims something never happens.
Consider the following statements: 1. Every individual in the population is equally susceptible host for Swine Flu. 2. Antibiotics have no role in the primary treatment of Swine Flu. 3. To prevent the future spread of Swine Flu in the epidemic area, the swine (pigs) must all be culled. Which of the statements given above is/are correct ?
- (a) 1 and 2 only
- (b) 2 only
- (c) 2 and 3 only
- (d) 1, 2 and 3
Answer(a) 1 and 2 only — everyone is susceptible and antibiotics do not treat a viral influenza; mass culling of pigs was not called for.
Marks the boundary of the medicines microbes have given us — antibiotics act on bacteria, so against a viral illness the whole class is useless, however many of them microbes have supplied.
Which one of the following statements is correct about effects of antibiotics on viruses?
- (a) Viruses are "non-living" entities but it can interact with antibiotics
- (b) Taking antibiotics cures viral infections
- (c) Viruses do not possess metabolic pathways on which antibiotics can function, whereas bacteria have such pathways
- (d) Viruses are resistant to antibiotics
Answer(c) Viruses do not possess metabolic pathways on which antibiotics can function, whereas bacteria have such pathways
Fixes the limit of the microbial medicines this question celebrates — an antibiotic works by attacking a living cell's chemistry, so a virus with no chemistry of its own is untouched.
- practice — not a real PYQ
Penicillin, the first widely used antibiotic, was obtained from
- (a)a mould of the genus Penicillium
- (b)a bacterium of the genus Lactobacillus
- (c)a virus
- (d)a green alga
Answer(a) a mould of the genus Penicillium — Fleming noticed in 1928 that it stopped staphylococci from growing.
- practice — not a real PYQ
Antibiotics are ineffective against viral infections because viruses
- (a)lack the metabolic machinery that antibiotics attack
- (b)are larger than bacteria
- (c)live only outside the human body
- (d)are killed by the body's heat instead
Answer(a) lack the metabolic machinery that antibiotics attack — with no cell wall, ribosomes or metabolism of their own, there is nothing for the drug to act on.