Yersinia

The Yersinia are one of Bactérie S of the family of the Enterobacteriaceae. The kind comprises ten S of which some are pathogenic for the Homme.

Yersinia pestis is the agent of the Peste. The others Yersinia cause more benign Maladie S, the Yersiniose S.

Ecology

Habitat

They are bacteria of the environment, present in water, the grounds and on the plants. They are also found on the sick animals or healthy carriers but also at the man.

Pathogenic role

This kind comprises several species responsible for yersinioses among which Yersinia pestis and Yersinia enterocolitica

The species Yersinia pestis

The Plague, sadly celebrates in the history by its Pandémie S loopholes, is today in regression: it disappeared from Europe since 1920 but of the stable hearths always persist in Asia, Africa and America. The human disease presents two principal clinical aspects: Without antibiothérapie, the plague evolves ineluctably to the death of its carrier.

The species Yersinia enterocolitica

They are responsible for infection intestinal which meet under any physical ages and all conditions but prevail in the young children.

They are characterized by abundant saddles, often bloody, associated with a fébricule and abdominal pains. The contamination is almost exclusively of origin food.

Bacteriological characters

Miscroscopic morphology

Aspect: the Yersinia are bacillus S negative Gram S, motionless, deprived of spores and capsules.

Grouping: Variable, They are presented insulated, in diplobacilles and chain.

Characters of culture

On ordinary Gélose after 24 hours of incubation to 37°C, the species presents colonies of small sizes (less 1mm of diameter) regular, smooth and brilliant, of type Smooth ; transparent or translucent. They evoke colonies of enterobacteries only after 36 to 48 hours of incubation.

Condition of culture

The characteristic of the Yersinia , compared to the others Enterobacteriaceae , lies in the fact that their metabolism is extremely thermodépendant, the variations of Température S are thus badly tolérées.
They have an optimal temperature of growth between 28 and 30°C, their slowly slowed down culture with 37°C and is almost stopped by a temperature ranging between 4 and 10°C without to cancel the risks of food toxinfections starting from cooled food products.

Culture media used

nonselective Mediums:
  • ordinary Gélose
  • Gélose BCP
selective Mediums:
  • Gélose Mac ConKey
  • Gélose Hektoen
  • Gélose Yersinia CIN

Biochemical characters

The kind Yersinia is characterized by a whole of negative natures:
  • Absence of fermentation of Lactose, absence of gas during the fermentation of the Glucose.
  • Absence of use of the Citrate like only source of Carbon on medium citrate-Simmons
  • Ansence of désaminase, lysin-décarboxylase and production of H2S

On the other hand there is constant fermentation of the Mannitol with a test ONPG positif.
Certain species are characterized by a very active urease like Yersinia entérocolitica and Yersinia pseudotuberculosis and others by the absence of this Enzyme like Yersinia pestis .

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