Batterjee Medical College

Dr. Manal El Said Head of Microbiology Department Staphylococci Staphylococcus aureus

Batterjee Medical College Staphylococcus aureus Diseases -lactamase Toxic shock syndrome Abscesses of many organs Endocarditis Gastroenteritis (food poisoning) Hospital-acquired pneumonia Surgical wound infections Sepsis.

Batterjee Medical College Staphylococcus aureus Habitat and Transmission Characteristics Gram-positive cocci in clusters. Coagulase-positive. Catalase-positive. Most isolates produce β-lactamase -lactamase. Main habitat is human nose & skin. Transmission is via the hands.

Batterjee Medical College Pathogenesis Staphylococcus aureus Three exotoxins: 1-Toxic shock syndrome toxin - Superantigen helper T cells release of lymphokines ( IL-2). 2- Enterotoxin - Superantigen - Food poisoning (has a short incubation period because it is preformed in food). 3-Scalded skin syndrome toxin: - Protease cleaves desmoglein in tight junctions in skin. - Protein A binds to heavy chain of IgG & prevents activation of complement.

Batterjee Medical College Pathogenesis Staphylococcus aureus Abscess containing pus is the most common lesion. Predisposing factors to infection - Breaks in the skin - Foreign bodies such as sutures - Neutrophil levels below 500/ml - Intravenous drug use right-sided endocarditis - Tampon use toxic shock syndrome

Batterjee Medical College Laboratory Diagnosis Staphylococcus aureus Gram-stained smear and culture. Yellow or gold colonies on blood agar. Coagulase-positive

Batterjee Medical College Laboratory Diagnosis Staphylococcus aureus

Batterjee Medical College Staphylococcus aureus Treatment ; Penicillin G for sensitive isolates Nafcillin (β-lactamase–resistant penicillins) for resistant isolates Vancomycin for isolates resistant to nafcillin (changes in binding proteins). About 85% are resistant to penicillin G (tolerant to penicillin) Plasmid-encoded -lactamase mediates most resistance.

Batterjee Medical College S. aureus methicillin-resistant (MRSA) is due to altered penicillin-binding proteins. MRSA can produce outbreaks of disease, especially in hospitals. The drug of choice is vancomycin, to which gentamicin is sometimes added. Daptomycin is also useful. S. aureus methicillin-resistant (MRSA) Treatment

Batterjee Medical College Trimethoprim-sulfamethoxazole or clindamycin can be used to treat non–life-threatening infections caused by these organisms. MRSA strains are resistant to all β -lactam drugs, including both penicillins & cephalosporins. Treatment S. aureus methicillin-resistant (MRSA)

Batterjee Medical College S. aureus with intermediate resistance to vancomycin Treatment Strains of S. aureus with intermediate resistance to vancomycin (VISA) & with complete resistance to vancomycin (VRSA) isolated from patients. These strains are methicillin-resistant as well, which makes them very difficult to treat. Daptomycin can be used to treat these infections Quinupristin-dalfopristin is another useful choice.

Batterjee Medical College Staphylococcus aureus Prevention ; Cefazolin is used to prevent surgical wound infections. No vaccine is available. Handwashing reduces spread.

Batterjee Medical College Diseases Characteristics Staphylococcus epidermidis Endocarditis on prosthetic heart valves Prosthetic hip infection Intravascular catheter infection Cerebrospinal fluid shunt infection Neonatal sepsis. Gram-positive cocci in clusters. Coagulase-negative. Catalase-positive.

Batterjee Medical College Pathogenesis Habitat and Transmission Staphylococcus epidermidis Normal flora of human skin & mucous membranes. Patient's own strains cause infection Transmission from person to person via hands. Glycocalyx-producing strains adhere well to foreign bodies such as prosthetic implants & catheters. It is low-virulence organism that causes disease: - Immunocompromised patients - Those with implants. It is a major cause of hospital-acquired infections.

Batterjee Medical College Laboratory Diagnosis Staphylococcus epidermidis Gram-stained smear and culture. Whitish, nonhemolytic colonies on blood agar. Coagulase-negative. It is sensitive to novobiocin (S. saprophyticus, is resistant).

Batterjee Medical College Laboratory Diagnosis Staphylococcus epidermidis

Batterjee Medical College Treatment Staphylococcus epidermidis Vancomycin plus either rifampin or aminoglycoside. It produces β-lactamases & is resistant to many antibiotics. Prevention There is no drug or vaccine.

Batterjee Medical College Staphylococcus saprophyticus Gram-positive cocci in clusters. Coagulase-negative. Resistant to novobiocin (S. epidermidis is sensitive). Community-acquired urinary tract infections in young women.