Some of these microorganisms normally populate the mucous membranes of the organism (especially oral, pharyngeal, intestinal and vaginal), without causing damage, sometimes collaborating with the physiological functions of the host organism. However, not all streptococci behave as commensals: some of these bacteria have a considerable pathogenic potential (as, for example, in the case of Streptococcus pneumoniae) and, by attacking the host, they can cause disease.
Other streptococcal species, under conditions favorable to them, can undergo a transformation from commensal to opportunist, penetrate the bloodstream and, having reached an organ, trigger a series of morbid processes, even severe ones (eg. Streptococcus viridans).
Streptococcus is mainly responsible for infections of the throat (pharyngitis, tonsillitis, etc.) and of the skin, which can cause serious complications, such as acute glomerulonephritis, rheumatic fever and endocarditis.
, a kind of defense weapon of the bacterium, since it hinders its phagocytosis by macrophages and neutrophils. Hyaluronic acid is considered an element of virulence of the pathogen, precisely because it delays phagocytosis by the cells of the immune system.
The cell wall is composed of antigens distinguished by the letters M (virulence factor with immunogenic power), R (antigen not involved in virulence or immunity) and T (epidemiological marker).
In the wall there are also group-specific carbohydrates, peptidoglycans and polysaccharide C. In addition to those listed above, among the virulence factors of streptococcus we also mention exotoxins (streptolysin O, streptolysin S and erythrogenic toxin) and exoenzymes (hyaluronidase, DNAse, streptokinase and NADase).
Streptolysin and Antistreptolysin Title
- Streptolysin is a haemolytic protein produced by some Streptococci (group A, C and G); variant O is one of the two hemolysins (the other is streptolysin S) produced by practically most of the strains of Streptococcus pyogenes (or group A beta hemolytic streptococcus) and from many of those belonging to groups C and G. In addition to causing hemolysis of red blood cells, this toxin has direct toxic effects on heart tissue.
- Antistreptolysin O (ASO, from the English "Anti-Streptolysin O") is a particular type of antibody that is produced by the immune system in response to streptococcal infection. More precisely, this is synthesized to neutralize the haemolytic properties of streptolysin O , a protein produced The letter "O" indicates that this immunogenic toxin is labile to oxygen.
- The antistreptolysin title is a serological test that allows to quantify the concentration of antistreptolysin present in the bloodstream. The exam is also called with the acronym TAS (abbreviation of "Title Anti Streptolysin") and the acronyms ASLO or ASLOT (from the "English" AntiStreptoLysin O Titer ").
The growth of streptococci in blood agar media seems to be favored by incubation in an atmosphere of CO2 at 10%, and by a temperature of 37 ° C. Only type D streptococci (analyzed below) require temperatures ranging from 15 ° to 45 ° C, even at high concentrations of salts (6.5%).
