The genus Staphylococcus comprises of both pathogenic and nonpathogenic organisms. They are Gram-positive, form irregular clusters of spherical cells, mesophilic, non-spore forming and highly resistant to drying. The common species are S. aureus, S. saprophyticus and S. epidermidis. Only the strains of S. aureus are pathogenic but the other two become pathogenic under special conditions of getting suitable portal of entry. They cause skin lesions and endocarditis. S. saprophyticus is associated with urinary tract infections. Symptoms caused by S. aureus are often seen in formation of abscesses in the form of localized pus forming lesions which occur in the skin. Its associated structures show boils, carbuncles, acne and impetigo. Very rarely, they cause pneumonia, osteomyelitis, endocarditis, cystitis (inflammation of urinary bladder), pyelonephritis (inflammation of kidney) and occasionally septicaemia due to enterotoxin contamination of staphylococcal enteritis. The end products of S. aureus are pathogenic. They cause clot formation, lyse WBC and active against RBC. Some times these are enterotoxic and cause gastroenteritis. The non-toxic properties are demonstrated due to DNase, gelatinase and the fibrinolysin staphylokinase. Such strains can be differentiated by virulent strains by a variety of tests as give in Table 14.2.
Dr. R. C. Dubey – PRactical Microbiology