Proteus mirabilis is a bacterial species of the order Enterobacteriales and the family Proteobacteria that lives facultatively anaerobically and is found in the human intestine as a protein decomposer. As pathogens, bacteria of this species can especially attack patients with a weakened immune system. They are then frequently involved in chronic urinary tract infections with the subsequent formation of kidney stones.
What is Proteus mirabilis?
Enterobacteriaceae are also called Enterobacteriaceae and form the only family of the order Enterobacteriales to date. Proteobacteria form a separate family in this bacterial order. Within this family, the genus Proteus corresponds to a gram-negative bacterial genus that, borrowing from the mutable sea god Proteus, is extremely mutable, especially externally. One species of this family is the bacterial species Proteus mirabilis. The individual strains of this species belong to the rod-shaped bacteria and are strongly flagellated peritrichously. Among their characteristics is their good motility. They do not form spores. The species Proteus mirabilis was discovered in 1885. The Erlangen pathologist Gustav Hauser is considered the first describer. The bacterium is in itself a beneficial bacterium, but at the same time it appears as a nosocomial pathogen and can thus cause pathological infections, which are included under hospital infections. The bacterium is especially useful within the intestinal flora, where it appears as a decomposer. As a pathogen, it can colonize the urinary tract. Detection as a pathogen is considered rather rare for this bacterium.
Occurrence, distribution, and characteristics
Bacteria of the species Proteus mirabilis do not form circumscribed colonies in gel media but, unlike other bacteria, spread over a wide area. This phenomenon is also known as the swarm phenomenon. The individual swarms often form a clear demarcation from other colonies. Proteus mirabilis are facultatively anaerobic. This means that they can grow in both oxygen-rich and oxygen-poor environments. Their metabolism is not dependent on oxygen, but neither is it dependent on the absence of O2. The bacteria produce the enzyme urease so that they can cleave urea. During the cleavage, ammonia is formed as a by-product, so that the pH of the nutrient medium increases and the growth conditions are improved. Apart from this, bacteria of the species Proteus mirabilis possess phenylalanine deaminase. The bacteria cannot metabolize lactose. They do not produce indole, which distinguishes them from Proteus vulgaris. The species spreads rapidly, with an optimum temperature of 34 to 37 degrees Celsius. Because of these temperature requirements, humans are an ideal nutrient medium for the bacterial species. The representatives of the species preferentially occur as harmless saprobionts in the human intestine and do not usually become a pathogen for healthy individuals. As pathogens, the bacteria are rather rarely transmitted from person to person, but rather originate from the body’s own bacterial community in the intestine.
Importance and function
Saprobionts such as bacteria of the species Proteus mirabilis decompose organic matter. In this way, they ensure closed material cycles within an ecosystem and break down accumulating organic material to use the resulting molecules for personal energy and building metabolism. In a narrower sense, the representatives of Proteus mirabilis practice saprophilia. They are therefore involved in putrefaction processes in the human intestine and contribute to the decomposition of organic material under anaerobic conditions, especially protein decomposition. Protein decomposition is a part of putrefaction. Protein-decomposing enzymes are also called proteolytic enzymes and decompose proteins (albumen) into small organic molecules. In the intestine, the bacteria Proteus mirabilis appear as such protein decomposers and correspond, so to speak, to a putrefactive bacterium that breaks down protein molecules into smaller molecules, which it feeds into its own metabolism via the cell wall and membrane. Putrefactive processes in the intestine correspond to anoxidative cleavage of organic substances, especially proteins. The decomposition of proteins is accompanied by the formation of substances such as cadaverine, neurine and methane. Since the bacteria do no harm in the human intestine and do not carry out their metabolism there at the expense of humans, for example, but with profit for humans, they are tolerated by the immune system as natural intestinal inhabitants.Humans even derive benefits from the bacteria because they create a closed cycle of materials.
Diseases and ailments
Bacteria of the species Proteus mirabilis can acquire pathologic significance in clinical practice and can act as causative agents. The most important in this regard is Proteus mirabilis in association with urinary tract infections. Among all urinary tract infections, up to ten percent are caused by this pathogen. Much less frequently, this bacterial species is involved in the inflammation of other organs. Bacteria of the species Proteus mirabilis are thus classified as facultative pathogens, which do not necessarily cause disease, but are potentially quite capable of doing so. As a rule, actual infections caused by the bacterium occur only in immunocompromised individuals. Wound infection or pneumonia and sepsis (blood poisoning), however, the bacterium causes even on weak people only in absolutely exceptional cases. If there is a chronic urinary tract infection caused by Proteus mirabilis, the urine pH may increase due to the bacterial metabolism. In extremely rare cases, gastroenteritis occurs in immunodeficient patients due to ingestion of high levels of germs through food. In this case, urinary stones are a common secondary disease. Indole-positive strains of Proteus mirabilis are rare but have developed multidrug resistance. Treatment follows resistance testing and can be with antibiotics such as cotrimoxazole, cephalosporin, or fluoroquinolone. Bacteria are naturally resistant to tetracyclines, colistin, tigecycline, and nitrofurantoin.
