In some systems, the prokaryotic Monera make up one of the five main groups of living things, including the bacteria, the cyanobacteria and the Archaea.
Bacteria are usually small cells that live and reproduce independently or in small colonies, and which have no separate membrane-bound organelles or nucleus.
Bacteria can usually only be seen with a microscope, although at least one bacterium, Thiomargarita namibiensis, is large enough to be seen with the naked eye.
Bacteria can be distinguished by staining properties, which show up when stains are used that are either taken up by chemicals in the cell wall, or not.
In 1884, Christian Joachim Gram invented his Gram stain which could be used for the classification of bacteria, because it only stained one type of cell wall.
One common stain used on bacteria is the Gram stain, used to divide bacteria in Gram positive (which take on a violet colour) and Gram negative bacteria.
The cell wall of a Gram negative bacterium is high in lipid content and low in peptidoglycans, the portion that the Gram stain normally attaches to.
Some bacteria form biofilms, layers of bacteria and complex molecules, often with other species involved, which behave like tissues in higher animals.
Bacteria form plaques of biofilm, complex interdependent communities of bacteria that interact and form layers similar to tissues in higher animals.
Some bacteria may be cultured in a Petri dish on a culture medium, but there are many more, perhaps as much as 96%, which cannot be cultured.
Most of the bacteria that cannot be cultured in a pure culture are those involved in biofilms, and which require other bacteria to be present before they grow.
Bubonic plague is a bacterial disease. The rats carry bacteria, fleas get them when they bite rats, and transfer them to humans when they bite the humans.
In 1843, Oliver Wendell Holmes observed the contagiousness of septicaemia, and suggested that medical staff should wash their hands to prevent its spread.
Ignaz Semmelweis could not explain why his innovative method designed to prevent childbed fever worked, though there could be no doubt that it did in fact work.
Semmelweis required those working under him to wash their hands in strong chemicals (chlorinated lime) before touching patients, and the fever rates plummeted.
Semmelweis died of the same fever he had done so much to fight, just a few years before the tide turned when Pasteur and Lister showed that his ideas worked.
In 1854, John Snow showed that whatever caused cholera, it could be found in the unboiled water from one well in London's Soho, coming close to a germ theory.
Hermann von Helmholtz anticipated Louis Pasteur by indicating that both fermentation and rotting were biological effects, but he did not follow this up.
In 1863, Pasteur showed that a micro-organism causes the souring of wine into vinegar, and as a response, invented pasteurization to kill the micro-organisms.
Bacteria can be killed in an autoclave if they are exposed for long enough to the combination of heat and steam, mainly because key proteins are denatured.
The bacteria that attack humans can generally be cultured, because the culture media that are used for this imitate the human body in many ways.
In 1882, Robert Koch described his method for isolating bacteria in pure culture by plating them on solid media, first gelatin, then agar later.
In 1876, Robert Koch cultured anthrax bacilli and showed that anthrax is caused by a specific organism, and in the same year, also stated Koch's postulates.
Robert Koch developed a set of four postulates, essential conditions that had to be met before an organism could be named as the cause of a particular disease.
Koch's first postulate: The organism should always be found present in an animal with the disease, and should never be found in one not suffering the disease.
Koch's second postulate: The organism must be cultured in a pure culture, containing only that one organism, away from the animal body, so it can be isolated.
Koch's third postulate: When such a culture of the purified organism is inoculated into a susceptible organism, characteristic disease symptoms should appear.
Koch's fourth postulate: The organisms reisolated and cultured from the experimental animals should be seen to be the same organism that was cultured earlier.
Even in old age, Florence Nightingale dismissed the 'germ-fetish'. She was one of the most reputable opponents of antisepsis, even as she promoted cleanliness.
In 1909, Charles Jules Henri Nicolle showed in a series of monkey trials in Tunis that the bacillus of typhus fever was transmitted by the body louse.
In 1910, Paul Ehrlich and Sachahiro Hata introduced the so-called magic bullet salvarsan to selectively kill the organism responsible for syphilis.