Enterobacteriaceae

The enterobacteries ( Enterobacteriaceae ) constitute one of most important the S of bacteria, as much from the quantitative point of view (more than one forty S) that from the qualitative point of view. It gathers many kinds thus, very ubiquitaires, and those are frequently met in infectious pathology like in bio-industries (Fermentation of Fromage medical S and dairy products, alcohols, treatments back-up troops, production of toxins of cosmetic use, drug company for the manufacture of antiviral agents, analyzes biological medical or veterinary taking away to insulate in culture the disease-causing agents, a great number of industries to take measurements of level of biological toxicity…).

Definition

One classically defines the enterobacteries by 7 criteria (but attention should be paid, with the rehandlings of families resulting from the new methods of the Taxonomie, certain kinds, not answering inevitably all these criteria, form part of this family today):

Gram- Bacilli of size average (Coccobacille, often polymorphic)
Nondemanding (easy culture)
Oxydase - (except Plesiomonas , Oxydase +)
Nitrate réductase + (able to reduce the Nitrate S in Nitrite S)
optional Aéro-anaerobes (able to push in presence or absence of dioxygene)
Fermentative of the Glucose (with or without production of gases)
Motionless or mobile by ciliature péritriche (very rare exceptions: Plesiomonas , polar ciliature)

The differences between many the kind S and Espèce S come from more precise criteria, like the Fermentation of various sugars, the production or not of sulfides, the presence or the absence of Enzyme S of the metabolism (β-galactosidase, Désaminase S, Décarboxylase S), the standard of fermentation (mixed butan-2,3-diol or acids). These criteria make it possible to gather the various kinds in “groups”, making easier the steps of identification more methodical and, but which do not correspond inevitably to realities of phylogenetic proximity (since they are only phenotypical criteria, like old the scientific Classification).

Ecology

Habitat

They are very widespread, some are found only in the environment, in particular in moist environments. The majority of the kinds comprise pathogenic species which cause disorders whose gravity enormously varies from one stock to another. Some are responsible for diseases of the plants (Phytopathogène) and others for the animal.

They are bacteria very Ubiquitaire S, i.e. one can find them in many ecosystems:

certain species are only Saprophyte S: moist environments especially, grounds, water, plants, food products,
of others are phytopatogenes: Erwinia , Pantoea ,
but the majority of the species are Commensale S, isolated in the intestine from the man and the animals, from where the name of enterobacteries.

They multiply generally as well at a host (Commensale S: Escherichia coli ) that in the environment (Saprophyte S: Serratia marcescens ), although certain S are adapted to one or the other of these habitats.

The enterobacteries commensales

They are the hosts of the man and the animals in which they reside mainly at the level of the intestine. One can however find them in the oral cavity, the wet areas of the skin in particular the Périnée, the nasal fossae and the female genital ways in which they can constitute a transit flora.

In the intestine, they represents a very large fraction of the aerobic flora of the intestine. They are found into large numbers on the level of the Côlon (of the ceacum to the rectum), it contribute to the degradation of the food residues and the production of intestinal gases; one speaks about flora of fermentation .

The species Escherichia coli plays there a paramount role because of its constant presence and of its broad prevalence on the other species, it constiturait 80% in the aerobic flora with a concentration bordering the 10^8e.Coli/g final saddle S. Other species have a presence less marked such as Proteus and Klebsiella like Citrobacter, Hafnia, Providencia, Enterobacter … with the more irregular presence.

The commensaux germs of the intestine or besides can be pathogenic by opportunism (urinary infections, superinfection…). Their pathology is nonspecific but holds especially of the " terrain" (the nature of the germ is not very important but the " terrain" , is very important for him. One immunodéprimé does not react like a healthy subject). The polyrésistance with the antibiotics which they can present comes from Plasmide S resistant.

Pathogenic enterobacteries

As we said, the pathogenic species have a great variability in their behavior and their aggressiveness at the host. One then distinguishes two groups from pathogenic enterobacteries: Strict pathogenic and opportunist pathogenic .

Strict pathogenic enterobacteries

Their presence in the organization is abnormal some is their number and often involve an infection whose gravity depends on their entrance point. Introduced by a contaminated food, they will cause intestinal disorders while adhering on the intestinal mucous membrane then while crossing the barrier entérocytaire. The symptoms are often characterized by important Diarrhée S followed of a dehydration (serious at the Nourrisson)

Certain species cause specific pathologies:

the species Salmonella typhi responsible for the Typhoid fever;
the species Shigella dystenteriae is the agent responsible for the bacillar dysentery;
the enterotoxic species Escherichia coli responsible for infantile gastro-enteritis or GEI;
the species Yersinia pestis responsible for the Plague.

These germs enteropathogenes are aggressive by them-even; their identification is thus capital.

Opportunist pathogenic enterobacteries

The opportunist enterobacteries do not have a sufficient pathogenic capacity to start a pathology at a healthy host. They are on the other hand likely to especially start an infection at a subject immunodéprimé like septicaemias in hospital medium (for example, Serratia , Klebsiella , etc…) what put them on the same foot as other germs of hospital such as the Staphylococcus and the Pyocyanique , respiratory, urinary, abdominal infections in particular Iatrogène S into post-operative.

They can be present in the intestine and form integral part of its flora commensale, thus the species Escherichia coli is responsible for urinary infection (in particular at the woman) at the time of, for example, constipations chroniques.
The species Klebsiella pneumoniae is sometimes responsible for respiratory infections.

The enterobacteries saprophytes

The enterobacteries saprophytes are present in the grounds, water, the plants and in any type of wet environment in general. They take part in the degradation of the organic matters. One counts among those: The Proteus (which lives as well in saprophytes as into commensaux), the Providencia, Enterobacter, Serratia, Hafnia … which are adapted to the environment.

List S

See too

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