What is the Gram reaction of Streptococcus pyogenes?
Streptococcus pyogenes (Group A streptococcus) is a Gram-positive, nonmotile, nonsporeforming coccus that occurs in chains or in pairs of cells. Individual cells are round-to-ovoid cocci, 0.6-1.0 micrometer in diameter (Figure 1).
Is pyogenes Gram-positive or negative?
pyogenes is a gram-positive, β-hemolytic streptococcus that is catalase negative. More than 150 different strains have been identified based on different M-protein types. It is a group A streptococcus based on its carbohydrate structure, according to Lancefield typing of β-hemolytic strains.
Which virulence factors of Streptococcus pyogenes allows the bacteria to avoid complement fixation?
Streptococcal pathogens have evolved to express virulence factors that enable them to evade complement-mediated attack. These include factor H-binding M (S. pyogenes) and pneumococcal surface protein C (PspC) (S. pneumoniae) proteins.
What makes Streptococcus pyogenes pathogenic?
1, it is understood that all S. pyogenes infections are initiated by adhesion of the bacterial organism to human epithelial cells, including those in the oral and nasal cavities and the skin. Bacterial pathogens express various molecules that are anchored in the cell wall as fimbrial-like structures.
How many virulence factors does Streptococcus pyogenes have?
Virulence factors of group A streptococci include (1) M protein and lipoteichoic acid for attachment; (2) a hyaluronic acid capsule that inhibits phagocytosis; (3) other extracellular products, such as pyrogenic (erythrogenic) toxin, which causes the rash of scarlet fever; and (4) streptokinase, streptodornase (DNase B …
Which toxin is produced by Streptococcus pyogenes?
Erythrogenic toxins, also referred to as streptococcal pyrogenic exotoxins, are secreted by strains of the bacterium Streptococcus pyogenes. SpeA and speC are superantigens, which induce inflammation by nonspecifically activating T cells and stimulating the production of inflammatory cytokines.
Is Streptococcus pyogenes Halotolerant?
Staphylococcus species are halotolerant, whereas Streptococcus species and many other organisms are inhibited by high concentrations of NaCl.
What is the main virulence factor of Streptococcus pneumoniae?
1. Polysaccharide capsule: S. pneumoniae’s extracellular polysaccharide capsule, the most important virulence factor (55), helps to initiate infection by allowing the bacterium to adhere to host cells and cause inflammation, while also providing protection from the host’s immune system (54, 55).
What are the virulence factors for Streptococcus pyogenes?
GAS strains express many virulence factors including surface protein M, streptolysins, streptokinase, hyaluronidase, peptidoglycan, and teichoic acid. Protein M is considered as the main virulence factor, limiting phagocytosis, disturbing the function of complement, and being responsible for adhesion [4].
Is Streptococcus salivarius Gram positive or negative?
Streptococcus salivarius is a gram positive bacterium found as part of the normal human oral microflora, predominantly colonising the tongue. Streptococcus salivarius K12 (isolated from the saliva of a healthy child) is a probiotic intended for use in oral cavity.
What are pathogen virulence factors?
Virulence factors are molecules produced by bacteria, viruses, fungi, and protozoa that add to their effectiveness and enable them to achieve the following: Specific pathogens possess a wide array of virulence factors.
Are toxins virulence factors?
Another class of virulence factors are called toxins. Toxins are chemicals that are released from bacteria that can damage host tissue in a multitude of ways. For example, the bacteria associated with causing the disease botulism releases a toxin called botulinum toxin.
Are capsules a type of virulence factor?
Capsule (also known as K antigen) is a major virulence factor of bacteria, e.g. all of the principal pathogens which cause pneumonia and meningitis, including Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitidis, Klebsiella pneumoniae, Escherichia coli, and group B streptococci have polysaccharide capsules on their surface.
What are the characteristics of Streptococcus?
Morphology and Growth Requirements. Microscopically,Streptococcus pyogenes is a spherical bacterium (cocci) that appears in chain-like formations.