Staphylococcus

■ Staphylococci are Gram-positive cocci occurring in clusters. They can be cultured on normal nutrient mediums both aerobically and anaerobically. The most important species from the viewpoint of human medicine is S. aureus. A number of extracellular enzymes and exotoxins such as coagulase, alphatoxin, leukocidin, exfoliatins, enterotoxins, and toxic shock toxin are responsible for the clinical symptoms of infections by this pathogen, which are observed in the three types invasive infections, pure toxicoses, and mixed forms. The antibiotics of choice for therapy of these infections are penicillinase-resistant penicillins. Laboratory diagnosis involves identification of the pathogen by means of microscopy and culturing. S. aureus is a frequent pathogen in nosocomial infections and limited outbreaks in hospitals. Hand washing by medical staff is the most important prophylactic measure in hospitals.

Coagulase-negative staphylococci are classic opportunists. S. epidermidis and other species are frequent agents in foreign body infections due to their ability to form biofilms on the surfaces of inert objects. S. saprophyticus is responsible for between 10 and 20 % of acute urinary tract infections in young women. ■

Staphylococci are small spherical cells (1 im) found in grapelike clusters. Staphylococci are nonmotile, catalase-producing bacteria. The genus Staphylococcus includes over 30 species and subspecies. Table 4.1 briefly summarizes the characteristics of those most important in the medical context. S. aureus (and E. coli) are among the most frequent causal organisms in human bacterial infections.

Table 4.1 Overview of the Staphylococcus Species That Affect Humans Most Frequently

Species

Parameter

S. aureus Coagulase-positive; colonies golden yellow. Local purulent infections: furuncles, carbuncles, bullous impetigo, wound infections, sinusitis, otitis media, mastitis puerperalis, ostitis, postinfluenza pneumonia, sepsis. Toxin-caused illnesses: food poisoning, dermatitis exfoliativa, toxic shock syndrome

S. epidermidis Coagulase-negative; sensitive to novobiocin; most frequent CNS* pathogen; opportunist; infection requires host predisposition; foreign body infections with discrete clinical symptoms

S. saprophyticus Coagulase-negative; resistant to novobiocin. Urinary tract infections in young women (10-20%); occasional nonspecific urethritis in men

CNS: coagulase-negative staphylococci

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