Diseases caused by Staph. aureus Lec.2 Diseases caused by Staph. aureus Superficial infections: Characterized by intense suppuration, local tissue necrosis and followed by local abscess formation. a. Impetigo (pyoderma). b. Folliculitis, furuncles (boils), styes c. Carbuncles d. Wound infection

Deep infections a- Osteomylitis b- Pneumonia c- Acute endocarditis d- Arthritis, Meningitis, Bacterimia, Septicemia and abscess of brain and kidney.

The disease caused by toxins as toxic shock syndrome toxin -1, 3. Toxin-mediated illness a- Toxic shock syndrome The disease caused by toxins as toxic shock syndrome toxin -1, A systemic disease characterized by abrupt onset, of high fever, vowiting, diarrhea, myalgias, a desequamative skin rash and hypotension with cardiac and renal failure in most severe cases it often occurs within 5 days after onset of the menses in young women who use tampons, but also occurs in children or in men with Staphylococcus wound infections.

b- Food poisoning Occure due to Staphylococcal enterotoxin, is characterized by a short incubation period (1-8 hours). It is self- limiting disease and recovery occurs within 24-48 hrs. c- Scalded skin syndrome Caused by strain of S. aureus that produce exofoliative toxin, mostly involves neonates and children less than 5 years old.

Diseases caused by coagulase- negative Staphylococci Community acquired coagulase-negative Staphylococci infections Hospital-acquired infections are due mostly to S. epidermidis and usually result from the colonization of prosthetic materials in patients with vascular catheters or implanted prostheses. Other species cause opportunistic infections such as endocarditis of prosthetic heart valves.

Laboratory diagnosis Specimens Smears Gram positive cocci. It is not possible to distinguish saprophytic (as S. epidermidis) from pathogenic (S. aureus) organisms on smears. Culture Specimens cultured on blood agar plates at 37°C for 24 hrs.

Tests used for identification of Staphylococci a- Mannitol salt agar The medium used for isolation and screening for nasal carriage of S. aureus, also used as test for identification of S. aureus. b- Catalase test This test used to differentiate Staphylococcus (positive) from Streptococcus and Pneumococcus (negative). c- Coagulase test The test used to differentiate S.aureus from other Staphylococci. H2 O2 H2O +O 2 H2O +O Catalase

Susceptibility testing Disc diffusion susceptibility testing should be done routinely on Staphylococcal isolates from clinically significant infections. Resistance to penicillin G be predicted by a positive test for β-lactamase. About 90% of S. aureus produce β Lactamase. Resistance to nafcillin (and oxacillin, methicillin) occurs in about 35% of S. aureus and 75% of S. epidermidis isolates. The gene code for nafcillin resistance can be detected by PCR.

Serologic and typing tests Serologic tests for diagnosis of S. aureus infection have little practical value. Antibodies to teichoic acid can be detected in prolong deep infection (Staphylococcal endocarditis). Molecular typing technique havebeen used to document the spread of epidemic disease-producing clones of S. aureus.

Treatment In serious multiple skin infections (acne, furunculosis). Tetracyclines are used for long term treatment. Abscess and other closed suppurating lesions are treated by drainage and antimicrobial therapy (penicillin, cephalosporines). Bacteremia, endocarditis, pneumonia and other severe infections due to S. aureus require prolonged intravenous therapy with a β- Lactamase- resistant penicillin. Vancomycin is reserved for naficillin resistant infection. Staph. epidermidis infections are difficult to cure because they occur in prosthetic devices where the bacteria can hinds themselves. Also S. epidermidis more resistant to antibiotics than S. aureus.

Epidemiology and control Staphylococci are colonizers of skin and mucosal surfaces. Staphylococci are transmitted from person to person, also the organism may be directly introduced into normally sterile sites, such as by a surgeon or nurse during surgery. The mode of spread is important in the hospitals where large proportions of medical staff and patients carry antibiotic resistant staphylococci in their nose or skin. In hospitals, areas at high risk for infection are the newborn surgery, ICUs, operating rooms and cancer chemotherapy. The persons with active Staphylococcal lesions, and carriers may have excluded from these area, and application of topical antiseptics to nasal or perineal carriage site. Rifampicin coupled with a second oral anti Staphylococcal drug sometime provide long term suppression and possibly cure of nasal carriage.

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