Bacteria are single-celled organisms, called prokaryotes because they have no nucleus, as opposed to eukaryotic cells which do have a nucleus. They were probably amongst the first living things to evolve on Earth and can now be found in almost every possible planetary niche from hot springs to radioactive waste. Some bacteria can photosynthesise, others can fix nitrogen from the atmosphere into the soil as nitrate and some live in environments toxic to other forms of life. There are about ten times as many bacteria living on and in a human (mostly in the gut) than there are human cells making up the body. From Wikpedia…
There are typically 40 million bacterial cells in a gram of soil and a million bacterial cells in a millilitre of fresh water. There are approximately 5×1030 bacteria on Earth, forming a biomass which exceeds that of all plants and animals.
Bacteria are vital to the recycling of elements like carbon in the environment and life on Earth would be impossible without them. However, they also cause some problems. A short selection of diseases caused by bacteria would include…
- Salmonella
- Salmonella bacteria are very common and certain types cause poisoning if present in large enough numbers on food. A different strain of salmonella bacterium causes typhoid fever which has a much more severe range of symptoms than food poisoning.
- Small mass outbreaks leading to few deaths
- Typhoid may affect millions in the developing world
- Salmonella bacteria are very common and certain types cause poisoning if present in large enough numbers on food. A different strain of salmonella bacterium causes typhoid fever which has a much more severe range of symptoms than food poisoning.
- Cholera
- From drinking water contaminated with Vibrio cholerae bacteria. Symptoms include vomiting, diarrhea and muscle cramps.
- 3-5 million victims each year, nearly all in the developing world, leading to 100,000 deaths
- From drinking water contaminated with Vibrio cholerae bacteria. Symptoms include vomiting, diarrhea and muscle cramps.
- Pertussis
- (Whooping cough) is a highly contagious bacterial disease that has cold-like symptoms that develop into a wracking cough that lasts for several weeks. There has been a vaccination available since the 1940s so it is again very rare in the developed world. It can be caught by vaccinated people but the symptoms will be much less severe. The effects of vaccination eventually wear off so people are recommended to have boosters later in life.
- 16 million victims per year/61,000 deaths
- (Whooping cough) is a highly contagious bacterial disease that has cold-like symptoms that develop into a wracking cough that lasts for several weeks. There has been a vaccination available since the 1940s so it is again very rare in the developed world. It can be caught by vaccinated people but the symptoms will be much less severe. The effects of vaccination eventually wear off so people are recommended to have boosters later in life.
- Tuberculosis
- (used to be called Consumption) A lung disease transmitted by the air via coughs and sneezes. Most infected people have no symptoms and it is thought that about ⅓ of the world’s population is infected. More effective treatment means that cases are falling but the numbers are quite big to begin with.
- About 9 million new cases each year leading to 1 to 1.5 million deaths
- (used to be called Consumption) A lung disease transmitted by the air via coughs and sneezes. Most infected people have no symptoms and it is thought that about ⅓ of the world’s population is infected. More effective treatment means that cases are falling but the numbers are quite big to begin with.
- Leprosy
- Despite its reputation, leprosy is not very contagious. It is quite rare, with most cases being found in India. It affects the skin, nerves, eyes and respiratory system. Treatment is provided for free by the World Health Organisation.
- New cases are now very rare – about 200,000 per year.
- Despite its reputation, leprosy is not very contagious. It is quite rare, with most cases being found in India. It affects the skin, nerves, eyes and respiratory system. Treatment is provided for free by the World Health Organisation.
Our chief defence against bacteria is good hygiene but many infections can be treated with antibiotics. Antibiotics are medicines that kill bacteria. The first one was penicillin, discovered by Alexander Fleming in 1928. Along with vaccination, the development of antibiotics led to a revolution in medicine with many diseases being nearly wiped out in the developed world. You may have heard in the news that some bacteria are becoming resistant to antibiotics, which is a fantastic example of evolution in action over a relatively short space of time.
The BBC has an excellent Q&A with Britain’s Chief Medical Officer Professor Sally Davies. In response to one of the questions, she says that in the UK the main reason that bacteria become resistant is the misuse of antibiotics prescribed to humans as opposed to agricultural use of antibiotics which is being blamed in many of the newspapers. Because so many antibiotics are used, bacteria have plenty of opportunity to be exposed to low doses of the drugs. Most will be killed but a few may have a gene that helps them to survive. These individuals will multiply and the gene will spread through the population – this is natural selection in action.
The search is on for the next effective antibiotic as the ones we currently use have decreased in efficacy.
Questions…
- Where would you find most genes in a eukaryotic cell?
- Suggest three organelles you would expect to find in a typical animal cell.
- What are the raw materials for photosynthesis?
- Plants absorb nitrate from the soil. What group of molecules do they make with it?
- What are the three main sites of digestion in a human?
Further reading…
Where There’s Muck There’s Brass
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