Conditionally pathogenic enterobacteria

Among the medically important species of conditionally pathogenic enterobacteria we include the genera Escherichia, Klebsiella, Enterobacter, Serratia, Citrobacter, which can be summarized under the name coliform bacilli and related genera Proteus, Morganella, Providencia. They are facultatively anaerobic gram-negative rods. They are catalase-positive and oxidase-negative. They reduce nitrates, ferment sugars, do not form spores. With the exception of Klebsiella, they are able to move with peritricheal flagella. Klebsielly are also the only representatives of this category to form shells, other genera only very rarely. They commonly occur in the environment and are part of the physiological intestinal flora. They have a complex antigenic structure on which the pathogenicity of each serovar is based. They are classified by more than 150 different thermostable O antigens, more than 100 thermolabile K antigens and about 50 H antigens. These bacteria are able to cause intestinal and extraintestinal diseases, most often the urinary system.

Escherichia spp.
The genus Escherichia includes a total of 8 specified species. The most medically discussed species is Escherichia coli. It is a common member of the physiological intestinal flora. It also occurs in small amounts as part of the physiological flora in the upper respiratory tract and genitals. It usually does not cause disease, only certain serovars are pathogenic or if it falls outside its normal range. It typically causes urinary tract infections. E. coli is said to be the most common pathogen in this area. Of the extrainstestinal infections, it is also responsible for meningitis, pneumonia, cholecystitis, appendicitis, peritonitis, postoperative wound infections and sepsis. It is often nosocomial in nature. Intestinal infections are caused by strains EPEC (enteropathogenic), ETEC (enterotoxigenic), EIEC (enteroinvasive), EHEC (enterohemorrhagic). Each of these named strains has a different mechanism of pathogenicity. However, everyone must be able to adhere to intestinal cells and some produce toxins. EPEC adheres tightly to the intestinal cells and causes changes in the intestinal cell, the most significant of which is the loss of microvilli. Sometimes it penetrates the cells. It causes severe watery diarrhea in children. It is more of a problem in developing countries. ETECs produce LT (thermolabile) or ST (thermostable) enterotoxins. Many serovars produce both types of enterotoxin, logically causing an even more severe course of the disease. It is a common cause of traveler's diarrhea. EIEC penetrates the intestinal cells, where it causes an inflammatory lesion. The disease mainly affects children in developing countries and tourists. EHEC remains, enterohemorrhagic also shiga-like toxigenic, verotoxigenic E. coli. It poses the greatest threat of these tribes. It can cause hemorrhagic diarrhea, as well as hemolytic uraemic syndrome (HUS). Lethality depends on the patient's age and virulence of up to 10% in E. coli type O157:H-, of which it has the strongest association with HUS type O157: H7. It is also dangerous in that it spreads easily. This is evidenced by the case of the EHEC 0104: H4 epidemic of 2011 in northern Germany. At that time, more than 3,800 cases were recorded, 54 people died.

Klebsiella spp.
The genus Klebsiella s now defined by ten species. It differs from other enterobacteria in that it regularly forms enclosures and is immobile. The most important pathogen of this genus is undoubtedly Klebsiella pneumonia. It lives in the intestine, in the oral cavity, in the upper respiratory tract, on the surface of the skin, but also in the surrounding environment. It causes pneumonia and urinary tract infections, especially in debilitated patients in hospitals. Here, it can also become a source of infection for newborns, causing meningitis and sepsis.

Enterobacter, Serratia, Citrobacter spp.
Enterobacter, Serratia and Citrobacter are more common as infections in hospitals. They attack bedsores, the respiratory and urogenital systems. They tend to be resistant to common antibiotics, so in hospitals there is a possibility of transmitting genetic information of resistance to ATB eg to Klebsiella. Enterobacter and Serratia are related to Klebsiella, Citrobacter, Salmonella. Overall, however, they have low pathogenicity. They are medically important Enterobacter cloacae, Enterobacter aerogenes, Enterobacter sakazakii, Citrobacter freundii, Citrobacter koseri, Serratia marcescens.

Proteus, Morganella, Providencia spp.
The genera Proteus, Morganella, Providencia have a lot of identical properties. They are characterized by a characteristic urea odor on the cultivation soils. They are a common part of the intestine, we can find them in the environment. Infections are usually caused endogenously. Their pathogenicity is low. In healthy individuals, they are able to cause at most infections of the urinary system, in the weak but also pneumonia, meningitis or sepsis. Species that cause these diseases include Proteus mirabilis, Proteus vulgaris, Morganella morganii, Providencia stuartii, Providencia rettgeri.

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