Sometimes bacteria multiply so rapidly they crowd out host tissues and disrupt normal function. Sometimes they kill cells and tissues outright. Sometimes they make toxins that can paralyze, destroy cells' metabolic machinery, or precipitate a massive immune reaction that is itself toxic.
Immune cascade
Two types of white blood cells — B and T cells — are incredibly powerful tools in the immune system's arsenal. B cells crank out billions of individualized antibodies, which uniquely bind to specific antigens.They can enter us through the eyes, nose, mouth or breaks in the skin (see How the Immune System Works for details). Once inside, they find a host cell to infect. For example, cold and flu viruses will attack cells that line the respiratory or digestive tracts. The new particles break free from the host cell.
Cytotoxic T lymphocytes, natural killer (NK) cells and antiviral macrophages can recognize and kill virus-infected cells. Helper T cells can recognize virus-infected cells and produce a number of important cytokines.
Intracellular bacterial pathogens can replicate within host cells, including macrophages, which ingest and kill microorganisms in a process called phagocytosis. By contrast, extracellular pathogens such as Pseudomonas aeruginosa multiply outside of cells.
Figure 2 - The human body is the home of millions of bacteria. Several body sites are full of bacteria and they are especially concentrated in the gut, in the throat and mouth, and on the skin.
Disinfectants such as bleach are used to kill bacteria or other pathogens on surfaces to prevent contamination and further reduce the risk of infection. Bacteria in food are killed by cooking to temperatures above 73 °C (163 °F).
Viruses do not have their own metabolism and require a host cell to make new products. The range of structural and biochemical (i.e., cytopathic) effects that viruses have on the host cell is extensive. Most viral infections eventually result in the death of the host cell.
Viruses depend on the host cells that they infect to reproduce. When it comes into contact with a host cell, a virus can insert its genetic material into its host, literally taking over the host's functions. An infected cell produces more viral protein and genetic material instead of its usual products.
Bacteria are found in every habitat on Earth: soil, rock, oceans and even arctic snow. Some live in or on other organisms including plants and animals including humans. There are approximately 10 times as many bacterial cells as human cells in the human body.
Basically, a virus must get inside a living cell to manufacture substances needed for their own reproduction and life cycle. Viruses are only active when inside a host because they can't undergo any chemical reactions of their own outside a host cell.
Viruses depend on the host cells that they infect to reproduce. When it comes into contact with a host cell, a virus can insert its genetic material into its host, literally taking over the host's functions. An infected cell produces more viral protein and genetic material instead of its usual products.
Bacteria and viruses can live outside of the human body (for instance, on a countertop) sometimes for many hours or days. Parasites, however, require a living host in order to survive. Bacteria and parasites can usually be destroyed with antibiotics.
When it comes into contact with a host cell, a virus can insert its genetic material into its host, literally taking over the host's functions. Some viruses may remain dormant inside host cells for long periods, causing no obvious change in their host cells (a stage known as the lysogenic phase).
Immune evasion strategies are those bacterial pathogens use to avoid or inactivate host defenses and ensure their own survival within a host. They employ tactics such as modulating their cell surfaces, releasing proteins to inhibit or degrade host immune factors, or even mimicking host molecules.
Some bacteria help to digest food, destroy disease-causing cells, and give the body needed vitamins. But infectious bacteria can make you ill. They reproduce quickly in your body. Many give off chemicals called toxins, which can damage tissue and make you sick.
There are two ways bacteria can harm the human body: toxicity – the bacteria produce toxins which damage specific tissues in the body. invasiveness – the bacteria multiply rapidly at the site of infection and overwhelm the body's defence mechanisms. The bacteria may then spread to other parts of the body.
The two ways that bacteria cause disease are via infection and creating toxins. The process of infecting the host is called invasiveness.
Bacteria are found in every habitat on Earth: soil, rock, oceans and even arctic snow. Some live in or on other organisms including plants and animals including humans. There are approximately 10 times as many bacterial cells as human cells in the human body.
Some viruses may have evolved from bits of DNA or RNA that "escaped" from the genes of a larger organism. The escaped DNA could have come from plasmids (pieces of naked DNA that can move between cells) or transposons (molecules of DNA that replicate and move around to different positions within the genes of the cell).
Toxigenesis, or the ability to produce toxins, is an underlying mechanism by which many bacterial pathogens produce disease. Endotoxins are cell-associated substances that are structural components of bacteria.
