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Bacteria and archaea are almost always microscopic, while a number of eukaryotes are also microscopic, including most protists, some fungi, as well as some micro-animals and plants. Viruses are generally regarded as not living and therefore not considered to be microorganisms, although a subfield of microbiology is virology , the study of viruses.
Microbiology (from Ancient Greek μῑκρος (mīkros) 'small' βίος (bíos) 'life' and -λογία () 'study of') is the scientific study of microorganisms, those being of unicellular (single-celled), multicellular (consisting of complex cells), or acellular (lacking cells).
Humans can be infected with many types of pathogens, including prions, viruses, bacteria, and fungi, causing symptoms like sneezing, coughing, fever, vomiting, and potentially lethal organ failure. While some symptoms are caused by the pathogenic infection, others are caused by the immune system's efforts to kill the pathogen, such as ...
Bacterial throat pain is often characterized by more pain on one side of the throat. An ear infection is more likely to be diagnosed as bacterial if the pain occurs in only one ear. [12] A cut that produces pus and milky-colored liquid is most likely infected. [14] Cause: Pathogenic viruses: Pathogenic bacteria
Infections may be caused by bacteria, viruses, fungi, and parasites.The pathogen that causes the disease may be exogenous (acquired from an external source; environmental, animal or other people, e.g. Influenza) or endogenous (from normal flora e.g. Candidiasis).
The English word fungus is directly adopted from the Latin fungus (mushroom), used in the writings of Horace and Pliny. [10] This in turn is derived from the Greek word sphongos (σφόγγος 'sponge'), which refers to the macroscopic structures and morphology of mushrooms and molds; [11] the root is also used in other languages, such as the German Schwamm ('sponge') and Schimmel ('mold').
Bacteria resist phage infection through restriction modification systems that degrade foreign DNA [138] and a system that uses CRISPR sequences to retain fragments of the genomes of phage that the bacteria have come into contact with in the past, which allows them to block virus replication through a form of RNA interference.
Viruses display a wide diversity of sizes and shapes, called 'morphologies'. In general, viruses are much smaller than bacteria and more than a thousand bacteriophage viruses would fit inside an Escherichia coli bacterium's cell. [39]: 98 Many viruses that have been studied are spherical and have a diameter between 20 and 300 nanometres.