Streptocoque

The streptocoques (the Streptococcus ) gather a vast whole of micro-organisms ubiquitaires and which includes/understands many S. Because of their number, one distinguishes the species Pathogène S from the species commensales and Saprophyte S.

The kind Streptococcus is often associated with the kind Leuconostoc because their characteristics are very close and not easily differentiable still today.

Ecology

The species saprophytes

Among the Streptococcus saprophytes, the streptocoques lactic ones are most numerous. Present in the environment and on the milk channels of Mammalian S, they is found in particular in milk. They are used in milk industry and cheese dairy, and in practically all the processing industries of milk. Species most usually met sont :
  • Streptococcus lactis , Streptococcus cremoris and Streptococcus diacetylactis   ; these three species are gathered under the name of Lactococcus lactis . Their action modifies qualities Organoleptique S of the lait : they are agents “of refining” or “deterioration” according to the human appreciation of the consequences that they have on milk.
  • Streptococcus thermophilus (or Streptococcus salivarius thermophilus ) is used mainly with manufacture as Yaourt S (in partnership with others Lactobacillus ).

The species commensales

The streptocoques ones belong to various flora commensales of the man and the animaux :
  • on the level of the mouth and the Oropharynx  : Streptococcus salivarius , Streptococcus mitis , Streptococcus sanguis , Streptococcus milleri …
  • on the level of the intestine  : the entérocoque S which constitute 10% of the aerobic flora of the intestine. They are required like witnesses of a possible fecal contamination of water and/or food.
They from now on are not regarded any more of Streptocoques, but as a group with whole share.

Pathogenic species

The pathogenic capacity of the Streptococcus are limited to certain species and depends enormously on the latter.
  • the Streptococcus pyogenes , of the group has of Lancefield, is at the origin of red anginas, of Infection S cutaneous (Impétigo), of Abcès, bronchopulmonary infections… The Angine S with streptocoque has can be associated with the Scarlatine  : they can also evolve to complications as the acute Rheumatoid arthritis (RAA) if the disease were not treated being young.
  • the Streptococcus agalactiae , of the group B of Lancefield, is responsible for infections at the newborn (Méningite S, Septicémie S) and sometimes for infections Vagin ales and urinary. In Pathology Veterinary, Streptococcus agalactiae is recognized as responsible for Mammite S at the Vache and can then be found in the Lait in abnormal quantity.
  • the Streptococcus pneumoniae (or Pneumococcus) is one of the principal persons in charge of mortality of infectious origin in the industrialized countries. It is also frequently responsible for Otite S and Sinusite S which can evolve to forms of purulent Méningite S. The pneumococcus is particularly dangerous for the elderly, the Nourrisson S and Nouveau-né S at which it causes bronchopulmonary infections leading to sometimes fatal complications of breathing.

Remarque :

Beaucoup of individuals is “  healthy carriers   ” and the streptocoques pathogenic ones without presenting lodge the signs of the disease. Thus close to 50  % of the individuals are healthy carriers of Streptococcus pneumoniae in their Rhinopharynx and 30 with 50  % of the women are carrying streptocoques group B in their cavity Vagin ale.

Bacteriological characters

Microscopic characters

They are hulls positive Gram S of 0,5 with 1  µm of diameter, presenting a typical grouping in chains, motionless, deprived of Spore S and seldom capsuled S.

the microscopic characters can slightly vary according to the species and particularly Streptococcus pneumoniae which is different by the regrouping into diplocoques (2  ×  hulls) capsuled.

Macroscopic characters and of culture

Condition of culture

Aéro-anaerobe optional, they develop as well in absence of oxygen as with. They are on the other hand sensitive to the conditions of culture, in particular of temperature and pH. The Streptococcus are Mésophile S (they have an optimal temperature of 37  °C) and Neutrophile S (pH  7 and acid medium very badly tolerated in particular).
the kind Streptococcus being very wide there exist exceptions. It is the case of Streptococcus thermophilus which proliferates at temperature close to 45  °C.

They are demanding germs  : they ask mediums nouveau riches in Nutriment S. However Streptococcus is cultivated on ordinary mediums but develops to with it little except for the streptocoques fecal ones.

Culture media

  • Mileux not sélectif :
    • Bubble glucose plugged   ;
    • Bubble heart-brain   ;
    • Medium Todd-Hewitt   ;
    • Medium Tryptone-salt   ;
    • Medium Trypcase-soya   ;
    • medium Columbia with fresh blood .
  • sélectifs  Medium;:
    • gélose with blood (blood of sheep + Azide)   ;
    • gélose Columbia + ANC (Acid nalidixic and Colimycine)   ;
    • gélose BEA (bile-esculine-azide) selective of streptocoques of the group D)   ;
    • Gélose Slanetz (highlighted of Streptococcus faecalis) .

Characteristics of the culture

  • Aspect in bouillon : disorder often not very homogeneous (presence of coagulats).
  • Aspect on gélose ordinaire : small colonies Translucent S with the variable diameters.
  • On gélose with blood the presence of colonies of certain streptocoques results in a halation  : it is the haemolytic character (two types : alpha : greenish halation because they transform hemoglobin into biliverdine and beta : halation clearly resulting from the total lysis of the red globules) .

Biochemical characteristics

The metabolic activity of streptocoques varies, but all the species are characterized by the absence of Catalase and the use of the way fermentaire for the degradation of some Glucide S without production of gas.

Antigenic character

The Sérotypage has an major importance in the classification of the Streptococcus , the majority of the required Antigène S are antigens of wall (in particular the polyoside C which is the antigen of group of streptocoques).

But of the antigens of capsule are also required mainly for the identification of Streptococcus pneumoniae .

Grouping of the Streptococcus

  • streptocoques the groupables is classified in 18 antigenic groups indicated by letters majuscules : of has to H and of K to T (certain groups comprise only one species).
  • streptocoques not the groupables is principalement :
    • the streptocoques commensaux ones of the flora oro-pharyngées or streptocoque viridans = streptocoque haemolytic alpha  .
    • pneumocoques : Streptococcus pneumoniae .

Species belonging to the kind Streptococcus

The old following names do not indicate any more of the species of the kind Streptococcus :

See too

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