<em>Salmonella enteritidis</em> b/w <em>Salmonella enteritidis</em>

Salmonella enteritidis

Salmonella enteritidis causes the illness known as food poisoning. Infection occurs when food, such as raw chicken, contaminated with the bacteria is eaten. The bacteria multiply inside the person's intestine, making toxins. Symptoms including vomiting, nausea, abdominal pain and diarrhoea. These usually start 8-48 hours after eating contaminated food.


Size comparison of different microbes

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Size comparison of different microbes

The diagram highlights the sizes of different microbes and compares them to other living things.

Microbes - bacteria, archaea, fungi, algae, protozoa and viruses - have been around for at least 3,500 million years and were the only life forms on Earth for most of that time. As the Earth cooled, liquid water formed and the first microbial life appeared. The conditions on Earth in the beginning were very hostile so the first microbes probably resembled the archaea, as they were able to live in the extreme environments such as the high temperature found on the cooling planet.

Around 2,800 million years ago, cyanobacteria, the largest and most diverse group of photosynthetic bacteria, probably appeared. This was an important development as these were the first organisms able to carry out aerobic photosynthesis. It is thought that cyanobacteria were responsible for raising the level of oxygen in the Earth’s atmosphere from less than 1 % to the 21 % of today. The presence of oxygen in the atmosphere allowed the evolution of new aerobic (oxygen using) species of microbes, which began to colonize every habitat on the planet.

Different species of cyanobacteria formed complex microbial communities with other types of microbes as they evolved, and these communities have left an extensive fossil record. They are fossilized in structures called stromatolites, dome-shaped mounds formed by the merger of mineral sediments into microbial mats.

Mammals and flowering plants are relative newcomers and only appeared around 100 million years ago.

Microbes affect every aspect of life on earth. They have an amazing variety of shapes and sizes and can exist in a wide range of habitats from hot springs to the icy wastes of Antarctica and inside the bodies of animals and plants.

Geobacter metallireducens

Find out more about this metal-eating microbe.

Bacillus thuringiensis

Discover how this bacterium can be used as a pesticide.