ID Board Review/Bacterial Diseases/Gram-positive cocci (GPC)/Staphylococcus aureus

background:#F8F5FD background:#AC83FD;border:1.2px solid black background;border:0px solid black background:#BFA0FD;border:0px solid black background:#E5D9FD;border:0px solid black background;border:0px solid black background;border:0px solid black background;border:0px solid black background:#E5D9FD; text-align:left S. aureus 400px400px Staphylococcus aureus is Gram Stain positive (above), and β-hemolytic on blood agar (below) Microlab Descriptions Preferred Media/Setting Readily grows well on animal blood agar (aerobic or anaerobic conditions). Isolates on 7.5-10% NaCl with mannitol.Becker K, Skov RL, von Eiff C: Staphylococcus, Micrococcus, and other catalase positive cocci. In Carroll KC, Pfaller MA, Landry ML, et al.: Manual of clinical microbiology, ed 12, Washington, DC, 2019, American Society for Microbiology, pp 367–398 Histology GPC, "cluster of grapes" Species Identification β-hemolytic Catalase (+) Coagulase (+) Oxidase (-) PYR (-) Normal Environment Skin flora Associated topics MRSA Clinical Presentations Skin Infections (most common presentations of S. aureus) Cellulitis Impetigo Folliculitis Mastitis Infection Surgical Wounds Infective Endocarditis, especially patients with left-sided valvular heart disease and patients with IV drug use S. aureus is often a cause of Osteomyelitis, and is the most common cause of Septic Arthritis S. aureus is the most common cause of Spinal Epidural Abscesses and Suppurative Intracranial Phlebitis Rarely causes meningitis, but when it does, it's usually after trauma, or Neurosurgery S. aureus rarely causes community pneumonia, but is often the cause of Nosocomial (Hospital Acquired) Pneumonia Septic Shock Prosthetic Joint Infection Risk Factorshttps://www.clinicalkey.com/#!/content/book/3-s2.0-B9780323673204000572?indexOverride=GLOBAL Skin/mucosal breaks or tears Foreign body/implant presence Prior viral illness (especially superimposed bacterial pneumonia) Defects in cellular or humoral immunity Diagnosis Bacteremia: Blood culture; low threshold for getting infective endocarditis blood cultures Sensitivities to differentiate between MSSA and MRSA MRSA Nares Swab PCR (to r/o MRSA pneumonias) Differential Diagnoses For skin infections without pus, consider Streptococcus Resistance Mechanism(s) Mec A gene → MRSA Management