What Is Strep Bacteria?

Streptococcus is another common type of bacteria from P. pyogenes, which is widely found in nature and human and animal feces and healthy human nasopharynx, most of which are not pathogenic. The medically important streptococci are mainly Streptococcus pyogenes, Streptococcus grass green, Streptococcus pneumoniae, Streptococcus agalactiae. The diseases that cause humans are mainly: purulent inflammation, toxins and hypersensitivity diseases. ^[1]

According to different diseases caused by streptococcus, pus, throat swab, blood and other specimens can be taken for examination.

The principle of prevention and treatment of streptococcal infection is the same as that of staphylococcus. Streptococcus is mainly transmitted by droplets. Patients and carriers should be treated in time to reduce the source of infection. Air, instruments, dressings, etc. must be disinfected. Patients with acute pharyngitis and tonsillitis, especially children, must be thoroughly treated to prevent the occurrence of hypersensitivity diseases. All Hemolytic A Streptococcus Pairs

Streptococcus biological characteristics

1. Gram-positive round or oval cocci arranged in chains. Capsules early in culture. There are pili-like structures outside the cell wall, containing M protein. After a long period of culture, aging bacteria or phagocytosis can be Gram-negative.

2. Higher nutritional requirements.

Blood agar plates formed off-white, smooth, small colonies, and most strains had beta hemolysis.

Long chains are easily formed in the liquid medium, and the bottom of the tube is flocculent.

3 The biochemical reaction was negative for enzymes. Generally, it does not break down inulin and is not dissolved by bile. Based on this, it is possible to distinguish between Streptococcus A and Streptococcus pneumoniae.

4 Antigen structure mainly includes:

protein antigens have type specificity, there are many, and the protein associated with pathogenicity is M protein.

Polysaccharide or C antigen has group specificity.

(3) The nucleoprotein antigen is non-specific. Not only are all types of streptococci identical, but they also cross staphylococci.

5. Resistance is weak and few resistant strains are formed. But resistant to drying.

Streptococcus pathogenicity

Group A streptococcus, also known as streptococcus pyogenes or hemolytic streptococcus, is one of the common pathogens that cause infection.

1. There are three main categories of pathogenic substances:

cell wall components

1) Lipoic acid (LTA): It forms the pili structure of group A Streptococcus with M protein, and enhances the adhesion to cells.

2) M protein: it is a surface protein component in the cell wall of group A streptococcus, with nearly 100 serotypes.

It has anti-phagocytosis and anti-bactericidal effects; It has common antigens with myocardium and glomerular basement membrane, so it is related to the occurrence of certain hypersensitivity diseases.

3) Peptidoglycan: it has the functions of causing heat and dissolving platelets.

4) Cell wall receptors: Facilitate the adhesion of bacteria to host cells.

5) F protein: it can bind to fibronectin on the surface of epithelial cells to facilitate the colonization of bacteria in the body.

Exotoxins

1) Pyrogenic exotoxin: It is the main toxic substance of human scarlet fever. Produced by group A streptococcus strains carrying lysogenic phage, heat-resistant, antigenic, three serotypes A, B, and C.

2) Streptolysin: it can lyse red blood cells and destroy white blood cells and platelets. Divided into two types according to the stability of O2:

SLO: Most strains of group A can produce SLO, which is a protein containing -SH group.

1) It is sensitive to oxygen and loses hemolytic activity when it encounters O2.

2) It has a toxic effect on a variety of cells and an acute toxic effect on the myocardium, which can cause cardiac arrest.

3) Strong antigenicity, SL0 antibody can prevent the toxic effects of SLO. The antibody titer of rheumatic fever patients is higher, and the activity cases are more significant. Generally, its titer is above 1: 400. Therefore, its content can be determined by For auxiliary diagnosis.

SLS: produced by most A, C, and G groups of Streptococcus. The hemolytic ring around the colonies of streptococci on blood agar plates is caused by this O2 stable SLS. It is non-antigenic.

invasive enzyme

1) Hyaluronidase: Hyaluronic acid can break down interstitial cells, making it easy for bacteria to spread in tissues.

2) Streptokinase (SK): It can convert the fibrinogen in the blood into fibrinase, so it can dissolve the blood clot or prevent the plasma from clotting, which is conducive to the spread of the bacteria in the tissue. Clinical use of recombinant streptokinase to treat acute myocardial infarction is better.

3) Chain enzyme (SD): It can degrade the highly viscous DNA in pus, make the pus thin, and facilitate the spread of germs. SK, SD has been made into enzyme preparations, which are used clinically to liquefy purulent exudates to facilitate the treatment of antibacterial drugs.

2. Caused by disease

Group A streptococci can be infected by air droplets, skin wounds, and contaminated food through multiple channels, causing the following three types of diseases:

purulent infection

1) Skin and subcutaneous tissue infections: lymphangitis, lymphadenitis, cellulitis, scabies, impetigo, etc.

2) Other system infections: tonsillitis, angina, sinusitis, otitis media, etc.

Toxic diseases scarlet fever, streptococcal toxin shock syndrome.

Hypersensitivity diseases rheumatic fever and acute glomerulonephritis.

Streptococcus immunity

After infection, a variety of antibodies can appear in the serum, mainly anti-M protein antibodies, which can enhance the role of phagocytic cells and protect the body from re-infection by streptococcus. However, because there are many types and there is no cross-immunity between the types, infection can be repeated.

A strong homotoxin immunity can be obtained after scarlet fever.

Streptococcus microbiological examination

1. Can take pus, nasopharyngeal swabs, blood and other specimens.

2. Direct smear microscopy: observe the characteristics of the bacteria and make a preliminary diagnosis.

3 Isolation, culture and identification: observe the colonies on the blood agar plate, if there is hemolysis, pay attention to identify with Staphylococcus;

If there is alpha hemolysis, attention should be paid to identify with Streptococcus pneumoniae: inulin fermentation test (-), bile lysis test (-).

4 Serological test: Anti-O test.

Anti-O antibodies in the serum of patients: about 250 units, to assist in the diagnosis of rheumatic fever.

> 400 units, active rheumatic fever.

Streptococcus prevention principles

1. Treat patients and carriers in time to reduce the source of infection.

2. Pay attention to disinfection of air, instruments and dressings.

3 Children with acute angina and tonsillitis must be treated thoroughly to prevent the occurrence of acute glomerulonephritis, rheumatic fever and subacute bacterial endocarditis.

4 Treatment: Group A streptococcal infection, penicillin G is the drug of choice.