Microorganisms

This chapter asks why microorganisms were not discovered before the microscope, what useful microorganisms do in medicine, agriculture and industry, and why ‘prevention is better than cure’ p. 2. COVID-19, first detected in Wuhan, China, has been categorised as a pandemic by the World Health Organisation (WHO) p. 3.

1.1 World of Microorganisms

Microorganisms are minute organisms that cannot be seen with the naked eye, only with the help of a microscope p. 4. Normal flora are microorganisms found in humans and animals which do not cause illness, such as Staphylococcus sp. and Corynebacterium sp. in the urethra p. 4. Staphylococcus sp. and Corynebacterium sp. live on the skin, and Escherichia coli, Lactobacillus sp. and Streptococcus sp. live in the small intestine p. 5. Normal flora competes with pathogens for nutrients, synthesises vitamin B12 and vitamin K, and stimulates the production of antibodies p. 5. Microorganisms are classified into five groups: fungi, algae, protozoa, bacteria and viruses p. 5.

Fungi can be macroscopic, such as mushrooms, or microscopic, such as yeast and mucor, which measure 10 µm to 100 µm p. 6. Yeast is unicellular and shaped like small spheres, while mucor is made up of a spherical sporangium and filamentous hyphae p. 6. Some fungi are saprophytes that feed on dead and decaying organisms, and some are parasites such as Trichophyton rubrum p. 7. Yeast reproduces asexually by budding, and mucor reproduces asexually by spore formation or sexually by conjugation p. 7. Fungi grow well in dark and moist places with decaying matter, faeces, animal skin and food p. 7.

Algae can be macroscopic, such as sea algae, or microscopic, such as Chlamydomonas sp. and Spirogyra sp., and they have chloroplasts that contain chlorophyll p. 8. Chlorophyll enables algae to carry out photosynthesis, and algae live in fresh water, salt water, moist soil and tree barks exposed to sunlight p. 9. Chlamydomonas sp. reproduces asexually by binary fission and sexually by conjugation, while Spirogyra sp. reproduces sexually by conjugation p. 9.

Most protozoa are unicellular, measure 5 µm to 250 µm and can be seen under the low powers of a light microscope p. 10. Paramecium sp. is slipper-shaped with cilia, while Amoeba sp. has no fixed shape and uses pseudopodia to move and engulf food by phagocytosis p. 10. Euglena sp. carries out photosynthesis and Plasmodium sp. is parasitic p. 10. Paramecium sp. and Amoeba sp. reproduce asexually by binary fission, and Paramecium sp. also reproduces sexually by conjugation p. 11.

Bacteria are unicellular, measure 0.2 µm to 10 µm, and can be seen under the high powers of a light microscope p. 12. They are named by shape: spherical (coccus), spiral (spirillum), rod (bacillus) and comma (vibrio) p. 12. The bacterial cell wall is made of amino acids and polysaccharides, not cellulose, and some bacteria have capsules, pili or a flagellum p. 12. Bacteria reproduce asexually by binary fission and sexually by conjugation, in which a plasmid transfers genetic material p. 13. Bacillus anthracis forms endospores with a strong protective coat to withstand extreme surroundings p. 13.

Viruses are the smallest microorganisms, less than 0.5 µm, and can only be seen under an electron microscope p. 14. They are made of nucleic acid (DNA or RNA) protected by a protein layer called the capsid, and their shapes include spherical, helix, polyhedral and complex p. 14. Viruses have no living characteristics outside their host and only reproduce by infecting host cells, as a bacteriophage does in a bacterium p. 15.

In Experiment 1.1, sterile nutrient agar is streaked with unwashed fingers, fingers washed with water only, and fingers washed with soap and water p. 17. The dishes are kept inverted in a dark cupboard at room temperature for three days before the colonies are counted p. 18. Damp conditions promote the growth of microorganisms, fungi and bacteria grow better in the dark, and ultraviolet light can kill them p. 19. The optimum temperature is 35 °C to 40 °C, low temperatures in a refrigerator retard growth, pH 7 is optimum for most microorganisms, and sufficient nutrients increase the growth rate p. 19. In Experiment 1.2, each group tests one factor on Bacillus sp., using a wire loop sterilised in a Bunsen burner flame until it glows p. 20. For temperature, dishes are kept at room temperature, in a refrigerator at 5 °C and in an incubator at 70 °C p. 24.

1.2 Useful Microorganisms

In medicine, insulin is made using recombinant DNA of E. coli, penicillin comes from Penicillium chrysogenum, and vaccines are made from rotavirus, Salmonella sp. and poliovirus p. 28. In agriculture, Nitrobacter sp. and Nitrosomonas sp. are nitrifying bacteria and Bifidobacteria sp. aids animal digestion p. 28. In industry, Lactobacillus bulgaricus is used in beverages, yeast in food, and Bifidobacteria sp. and Lactobacillus subtilis in leather goods p. 28. Green biotechnology makes it possible to use microorganisms to treat sewage and to produce eco enzymes from agricultural waste fermentation p. 29.

Eco enzyme is a natural product obtained from the fermentation of agricultural waste such as fruit or vegetable waste p. 30. Its enzymes decompose fat and grease into smaller molecules that do not clog drainage, while surfactants in chemical cleaners emulsify grease into foam that clogs drainage p. 30. Eco enzyme needs no scrubbing, costs less, produces less waste and is environmentally friendly p. 30. Lactobacillus sp. bacterial serum treats wastewater and sludge in drainage systems, and it also removes odour, makes compost, produces enzyme and improves the fishing industry p. 31.

1.3 Prevention and Treatment of Diseases Caused by Microorganisms

Harmful microorganisms that cause diseases are called pathogens p. 33. Aseptic technique is a healthcare procedure to prevent infections caused by pathogens or remove existing ones, in line with the phrase ‘prevention is better than cure’ p. 33. Aseptic techniques include sterilisation, boiling, and the use of antiseptics, disinfectants and radiation p. 33. Sterilisation kills or eliminates microorganisms using heat, chemical substances, radiation, high pressure or filters p. 34. A temperature above 130 °C in an autoclave kills microorganisms and their spores, and a micron filter removes particles of 0.1 µm to 10 µm from liquids p. 34. Boiling water at 100 °C kills microorganisms on milk bottles, injection needles and dental equipment p. 34.

Antiseptics are applied on skin or wounds to prevent infections, for example acriflavine, povidone and 70% isopropyl alcohol, while proflavine only blocks the growth of microorganisms p. 35. Disinfectants such as bleach, hydrogen peroxide and liquid chlorine are used on non-living things such as bed sheets, toilets and swimming pools, not on skin p. 35. Ionising radiation such as ultraviolet rays, X-rays and gamma rays kills microorganisms, and ultraviolet rays are used in operating theatres p. 36. Antibiotics treat infections caused by bacteria but are not effective on viral infections; antibiotic resistance happens when an antibiotic loses its ability to kill bacteria p. 36. Excessive use, inaccurate use and not taking antibiotics for the prescribed duration cause antibiotic resistance, which makes us vulnerable to more diseases p. 36.

In Experiment 1.3, filter paper discs with penicillin of different concentrations are placed on agar with Bacillus sp., and the area of the clear region around each disc is measured p. 38. Sir Alexander Fleming studied the action of the Penicillium sp. fungus on bacterial growth and was the first person to discover antibiotics p. 39. Pneumonia, caused by the bacterium Streptococcus pneumoniae, is treated with an antibiotic such as penicillin p. 40. Athlete’s foot, caused by the fungus Trichophyton rubrum, is treated with an antifungal such as clotrimazole, and shingles, caused by the Varicella-zoster virus, is treated with an antiviral such as acyclovir p. 40.