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A microorganism or microbe is an organism that is so small that it is invisible to the naked eye. The term is synonymous by usage to single- celled organism, even though some unicellular protists are visible to the naked eye, and some colonial species are microscopic. Microorganisms may be found almost anywhere in the taxonomic structure. Bacteria and archaea are always or almost always microscopic, as are most protists. Even some fungi, a primarily macroscopic taxon, are microorganisms. Disease-causing salmonellae have recently been re-classified into a single species, Salmonella enterica, which has numerous strains or serovars. Salmonella typhi is a well know serovar that causes typhoid fever. Other salmonellae are frequent causes of foodborne illness, and can especially be caught from poultry. In the mid to late 20th century, Salmonella enterica serovar Enteritidis was a common contaminant of eggs. This is much less common now with the advent of hygiene measures in egg production and the vaccination of laying hens to prevent samonella colonisation. Many different salmonella serovars also cause severe diseases in animals other than human beings. Click on following items to see more information: Agrobacterium, Antibiotics, Antibiotics, Antimicrobials, Bacillus, Bacillus subtilis, Microorganisms, Microbiological, Bacteriological, Microorganism, Bioremediation, Candida albicans, Cell suspensions, Clostridia, Culture medium, Escherichia coli, Escherichia coli, Escherichia coli, Escherichia coli, Escherichia coli, Enterobacteriacea, Fermentations, Yeasts, Gram negative, Haemophilus, Lactobacillus, Microorganism, Microbiological, Microorganism, Neisseria, Penicillin, Proteus, Pseudomonas, S. cerevisiae, S. cerevisiae, Salmonella typhimurium, Sepsis, Staphylococcus aureus, Staphylococcus, Streptococci, Thermophile, Xanthomonas Some pathogens (such as Yersinia pestis, which caused the Black Plague, and the aforementioned Variola virus) have been found responsible for massive amounts of casualties and have had numerous effects on afflicted groups. Of particular note in modern times is HIV/AIDS, which is known to have infected several million humans globally, threatening entire populations in certain parts of the world, as well as the recently emerged Severe Acute Respiratory Syndrome, or SARS. In 1930, 2 major categories of H. influenzae were defined: the unencapsulated strains and the encapsulated strains. The pathogenesis of H. influenzae infections is not completely understood, although the presence of the encapsulated type b (HiB) is known to be the major factor in virulence. Their capsule allows them to resist phagocytosis and complement-mediated lysis in the non-immune host. Unencapsulated strains are less invasive, but they are able to induce an inflammatory response that causes disease. Vaccination with Hib conjugate vaccines is effective in preventing infection, and several vaccines are now available for routine use.
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