Staphylococcus is a genus of Gram +ve, round shape bacteria that are arranged in grape-like clusters. The organisms of this genus are the commonest cause of suppurative lesions.
It was first isolated by Sir Alexander Ogston and he gave the name Staphylococcus for the typical arrangement of the cocci in grape-like clusters.
There are about 40 species of Staphylococcus exists in nature but the medically important species for humans includes –
- Staphylococcus aureus – pathogenic, causes pyogenic infections
- Staphylococcus epidermidis – Skin commensal
- Staphylococcus saprophyticus – opportunistic pathogen
The pathogenic species of Staphylococcus i.e. S. aureus have certain characteristics like the production of enzymes Coagulase, Phosphatase, Deoxyribonuclease and ability to ferment mannitol sugar. These tests are really helpful in differentiating S. aureus from other species.
Also, Staphylococci are classified on the basis of Coagulase enzyme production as Coagulase +ve and Coagulase –ve.
There are various strains of Coagulase +ve Staphylococcus which produce Golden yellow colonies on the Nutrient agar media (NAM) and are called as Staphylococcus aureus or simply Staph aureus. These strains are toxigenic and cause various pathologies in humans.
The Coagulase –ve strain strains that are non-pathogenic and non-toxigenic to humans, produce white color colonies on Nutrient agar medium (NAM) and are called Staphylococcus epidermidis. This species of Staphylococcus was earlier termed as Staphalbus by Rosenbach.
The third medically important species of Staphylococcus i.e. S. saprophyticus which is an opportunistic pathogen is a Coagulase –ve species and produces Lemon yellow color colonies on the Nutrient agar medium (NAM) and earlier termed as staphcitreus by Passet.
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MORPHOLOGY OF STAPHYLOCOCCUS AUREUS Shape – Round shape (cocci) Size – 1 micron (diameter) Arrangement of cells – Grape-like clusters Motility – Non-motile Flagella – Non-flagellated Spores – Non-sporing Capsule – present in some strains Gram Staining reaction – Gram +ve CULTURE REQUIREMENTS OF STAPHYLOCOCCUS AUREUS ⇒ Special requirements – No special requirements for culture, readily grows on Ordinary culture media. ⇒ Optimum temperature – 10-42°C ⇒ Optimum pH – 7.4-7.6 ⇒ Salt ...Continue Reading.....
There are so many biochemical tests for Staphylococcus aureus, the well known causative agent of localized suppurative lesions. However, only a few reactions are most commonly used and are medically important for distinguishing pathogenic staphylococcus i.e. S. aureus from other non- pathogenic Staphylococci which are as follows: ⇒ Beta hemolysis on Blood agar ⇒ Golden yellow pigment production ⇒ Coagulase production ⇒ Mannitol Fermentation ⇒ Gelatin liquefaction ⇒ Phosphatase production ⇒ Deoxyribonuclease (DNase) production ⇒ Tellurite reduction Check ...Continue Reading.....
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 ...Continue Reading.....
A range of laboratory diagnostic methods has been developed to support patient management and disease control. The choice of diagnostic method depends on the purpose for which the testing is done (e.g. clinical diagnosis, epidemiological survey, vaccine development), the type of laboratory facilities and technical expertise available, costs, and the time of sample collection. Ideally, the clinical Diagnosis of the Staphylococcal infection is done as follows: SPECIMEN COLLECTION The specimen ...Continue Reading.....
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