TOXINS OF STAPHYLOCOCCUS AUREUS
Staphylococcus aureus produces a wide variety of toxins which are important virulence factors and produces various diseases in humans. These are as follows:
1.) Hemolysin – Staphy aureus produces four antigenically distinct types of hemolysin called as alpha, beta, gamma & delta. All these types of toxin are exotoxins. Of these, Alpha-hemolysin is the most important in Pathogenicity. Alpha-hemolysin is Cytotoxic, Leucocidal, and Dermonecrotic also damages the Circulatory system and Muscle tissues.
2.) Leucocidin – It was discovered by Van de Velde in 1894 named after Sir Philip Noel Panton and Francis Valentine in 1932 as Panton-Valentine Leucocidin (PVL). It is composed of two components as S (slow) and F (fast) which damages the white blood cells, mainly the Neutrophils (Polymorphonuclear leucocytes) and Macrophages.
3.) Enterotoxin – The toxin is responsible for the Staphylococcal food poisoning, characterized by Nausea, Vomiting, and Diarrhea which most commonly occurs within the 2-6 hours of consuming contaminated food. Staphylococcal enterotoxin can withstand boiling at 100°C for few minutes, is a Superantigen, acts directly on ANS and produces the illness.
4.) Toxic Shock Syndrome Toxin (TSST) – Some strains of Staphy aureus causes the Toxic shock syndrome (TSS). The TSST is a Superantigen, which causes the syndrome commonly characterized by Fever, Vomiting, Diarrhea, Hypotension, Erythematous rashes and hyperemia of the mucous membrane.
5.) Exfoliative a.k.a Epidermolytic toxin – There are two types of Exfoliative toxin – A & B, produced by various strains of Staphylococcus aureus. The Exfoliative toxin A is heat stable whereas the Exfoliative toxin B is a heat labile toxin. Epidermolytic toxin splits the skin and results in the blister formation and leads to desquamation producing the Staphylococcal Scalded Skin Syndrome (SSSS). In Newborns, the severe form of SSSS is known as Ritter’s disease. The milder forms of SSSS are known as Bullous impetigo (in adults) & Pemphigus neonatorum (in newborns).
PATHOGENESIS OF STAPHYLOCOCCUS INFECTION
⇒ Staphylococcus aureus is the most important Gram +ve cocci that cause pyogenic lesions which are localized in nature.
⇒ It causes a large no. of diseases in humans which can be classified as cutaneous infections, Deep & Systemic infections, Food poisoning, Nosocomial infection, Exfoliative disease and Toxic Shock Syndrome.
⇒ The Cutaneous infections include Boils, Carbuncles, Styes, Pustules, Impetigo, Wound and burn infections.
⇒ The deep and Systemic infections include Osteomyelitis, Tonsillitis, Pharyngitis, Pneumonitis, Sinusitis, Bacteremia, and Septicemia.
⇒ The Staphylococcal food poisoning caused by Staphylococcal enterotoxin which usually occurs in 2-6 hours due to the ingestion of preformed enterotoxin of Staphylococcus aureus present in the contaminated food.
⇒ The Staphylococcal infections are the most common hospital-acquired infection which usually Urinary Tract Infections (UTI) and Respiratory tract infections (RTI).
⇒ Some Strains of Staphylococcus causes skin Exfoliative diseases by the production of Epidermolytic toxin and most commonly results in Staphylococcal Scalded Skin Syndrome (SSSS).
⇒ Staph aureus also causes Toxic Shock Syndrome (TSS) by the production of Toxic shock Syndrome Toxin (TSST), characterized by High fever, Hypotension, Vomiting, diarrhea, and rashes.