Семейство Enterobacteriaceae: характеристика и значение.

Family of bacteria

Enterobacteriaceae is a large family of Gram negative bacteria. It includes over 30 genera and more than 100 species. Its classification above the level of family is still a subject of debate, but one classification places it in the order Enterobacterales of the class Gammaproteobacteria in the phylum Pseudomonadota. In 2016, the description and members of this family were emended based on comparative genomic analyses by Adeolu et al. Enterobacteriaceae includes, along with many harmless symbionts, many of the more familiar pathogens, such as Salmonella, Escherichia coli, Klebsiella, and Shigella. Other disease causing bacteria in this family include Enterobacter and Citrobacter. Members of the Enterobacteriaceae can be trivially referred to as enterobacteria or "enteric bacteria", as several members live in the intestines of animals. In fact, the etymology of the family is enterobacterium with the suffix to designate a family (aceae)—not after the genus Enterobacter (which would be "Enterobacteraceae")—and the type genus is Escherichia.

Members of the Enterobacteriaceae are bacilli (rod shaped), and are typically 1–5 μm in length. They typically appear as medium to large sized grey colonies on blood agar, although some can express pigments. Most have many flagella used to move about, but a few genera are nonmotile. Most members of Enterobacteriaceae have peritrichous, type I fimbriae involved in the adhesion of the bacterial cells to their hosts. They are not spore forming.

Like other Pseudomonadota, Enterobacteriaceae have Gram negative stains, and they are facultative anaerobes, fermenting sugars to produce lactic acid and various other end products. Most also reduce nitrate to nitrite, although exceptions exist. Unlike most similar bacteria, Enterobacteriaceae generally lack cytochrome c oxidase, there are exceptions. Catalase reactions vary among Enterobacteriaceae.

Many members of this family are normal members of the gut microbiota in humans and other animals, while others are found in water or soil, or are parasites on a variety of different animals and plants.

Escherichia coli is one of the most important model organisms, and its genetics and biochemistry have been closely studied. Some enterobacteria are important pathogens, e. g. Salmonella, or Shigella e. g. because they produce endotoxins. Endotoxins reside in the cell wall and are released when the cell dies and the cell wall disintegrates. Some members of the Enterobacteriaceae produce endotoxins that, when released into the bloodstream following cell lysis, cause a systemic inflammatory and vasodilatory response. The most severe form of this is known as endotoxic shock, which can be rapidly fatal.

Enterobacteriaceae was originally the sole family under the order 'Enterobacteriales'. The family contained a large array of biochemically distinct species with different ecological niches, which made biochemical descriptions difficult. The original classification of species to this family and order was largely based on 16S rRNA genome sequence analyses, which is known to have low discriminatory power and the results of which changes depends on the algorithm and organism information used. Despite this, the analyses still exhibited polyphyletic branching, indicating the presence of distinct subgroups within the family. In 2016, the order 'Enterobacteriales' was renamed to Enterobacterales, and divided into 7 new families, including the emended Enterobacteriaceae family. However, this division was not officially proposed as the subfamily rank is generally not used.

Several Enterobacteriaceae strains have been isolated which are resistant to antibiotics including carbapenems, which are often claimed as "the last line of antibiotic defense" against resistant organisms. For instance, some Klebsiella pneumoniae strains are carbapenem resistant. Various carbapenemases genes (blaOXA 48, blaKPC and blaNDM 1, blaVIM and blaIMP) have been identified in carbapenem resistant Enterobacteriaceae including Escherichia coli and Klebsiella pneumoniae.