Staphylococcal Infections

Introduction
Staphylococci are common bacteria that colonize human skin and mucous membranes. Staphylococci are the leading cause of bacteremia, surgical wound infection and the second leading cause of nosocomial infections. Staphylococci are responsible for the following syndromes: superficial and deep pyogenic infections systemic intoxications urinary tract infection Within the genus, Staphylococcus aureus is the most important human pathogen, in part because of increasing resistance to antimicrobial agents. Other important Staph pathogen include: Staphylococcus epidermidis [prosthetic materials adherance and nosocomial infections] and Staphylococcus saprophyticus [urinary tract infection]

Deresiewicz, R.L., and Parsonnet, J., Staphylococcal Infections., In Harrison's Principles of Internal Medicine 14th edition, (Isselbacher, K.J., Braunwald, E., Wilson, J.D., Martin, J.B., Fauci, A.S. and Kasper, D.L., eds) McGraw-Hill, Inc (Health Professions Division), 1998, p. 875.

Staphylococcal Intoxications:
Toxic Shock Syndrome (TSS): caused by toxic exoproteins produced by S. aureus. Symptoms: hypotension, fever, rash, multiorgan dysfunction. Treatment: decontamination of the anatomical site producing toxin, fluid replacement and administration of anti-staphylococcal agents. Effective drugs : semisynthetic penicillins {nafcillin, oxacillin} and the possibly more effective protein synthesis inhibitor clindamycin. Food poisoning: caused by the presence of staphylococcal enterotoxins (SEs) which are resistant to cooking temperatures. Most cases are self-limiting with symptoms resolving between 8 to 24 h. following onset of nausea, vomiting, abdominal pain and diarrhea. Staphylococcal Scalded Skin Syndrome: Cutaneous diseases of differing severity caused by staphylococcal enterotoxins (SE)- producing strains of Staph. aureus. Depending on the manifestation, mortality from dehydration and sepsis can range from 3% in children to 50% in adult patients. Treatment: fluid/electrolyte management, care to denuded skin and antistaphylococcal drugs.

Skin and Soft Tissue Infections
Skin and Soft-tissue Infections: S. aureus is the most common cause and may be manifest as boils and carbuncles. S. aureus causes bullous impetigo, a cutaneous infection seen primarily in children. Cellulitis, an infection of subcutaneous tissue, may be caused by S. aureus but more commonly by ß-hemolytic streptococci. Post-surgical/traumatic wound secondary infection is most likely due to Staph. aureus.

Respiratory Tract Infection
S. aureus may cause pneumonia, but this occurence is rare in the absence of predisposing host factors or epidemiological factors that impair immunological defense mechanisms. S. aureus is occasionally the cause of sore throat with exudative pharyngitis. S. aureus is a significant cause of chronic sinusitis and sphenoid sinusitis

Central Nervous System Infection
S. aureus: important cause of brain abscess. S. aureus: common cause of space-filling suppurative intracranial infections such as subduralempyema [osteomyelitis of the skull] S. aureus: most common cause of spinal epidural abscess. S. aureus: most common cause of septic intracranial thrombophlebitis [arising from facial soft tissue infection, sinusitis, or mastoiditis]

Endovascular Infection
S. aureus: most common cause of acute bacterial endocarditis of native and prosthetic cardiac valves. [The microbe tends to adhere and infect damaged tissue]

Musculoskeletal Infection
S. aureus: most common cause of acute osteomyelitis in adults and a prominent cause in children. S. aureus: prominent cause of chronic osteomyelitis. S. aureus: significant cause of septic arthritis & septic bursitis

Drug Treatment
Although most pathogenic strains of S. aureus are resistant to penicillin, efficacious semi-synthetic penicillinase-resistant drugs have been developed. Nafcillin and oxacillin (ß-lactamase resistant) are effective and drugs of choice in treating staphylococcal infection. Combinations that include a penicillinase-inhibitor and penicillin are also efficacious but may be best reserved for mixed-infections. On the basis of potency, cost and spectrum of coverage, first-generation cephalosporins (e.g. cefazolin) would be appropriate. Vancomycin (parenteral) is efficacious as are dicloxacillin and cephalexin (oral, for minor infection or continuous treatment) An example of synergy in treating S. aureus bacteremia (endocarditis) is the combinaton of an aminoglycoside/ß- lactam combination. Rifampin in combination with a ß- lactam antibiotic or vancomycin is effective in otherwise refractory disease, but should not be employed as monotherapy due to toxicity due to rapid resistance development. ifampin should be reserved for refractory infections in which the added risk of rifampin toxicity is justified.