Snapshot A 23-year-old woman presents to the emergency department with fever, chills, and watery diarrhea. Her symptoms began approximately 1 day after menstruation began. Her temperature is 102°F (38.9°C), blood pressure is 75/50 mmHg, pulse is 125/min, and respirations are 20/min. Physical examination is notable for a diffuse erythematous rash and desquamation of the palms and soles. Introduction Classification gram-positive cocci in clusters Microbiology properties facultative anaerobes catalase positive neutralizes its own hydrogen peroxide, which results in the hosts phagocytes inability to produce reactive oxygen species to combat infection (especially in patient's with chronic granulomatous disease ) coagulase positive coagulase activates prothrombin, leading to clotting leads to fibrin formation around this organism differentiates S. aureus from S. epidermidis and S. saprophytic β-hemolytic complete hemolysis of red blood cells on an agar plate appears gold in sheep blood agar protein A binds to the Fc region of the IgG antibody this prevents opsonization and phagocytosis hemolysins damages red blood cells, platelets, neutrophils, and macrophages leukocidins damages white blood cells penicillinase a secreted form of β-lactamase, which makes S. aureus resistant to penicillins toxins exfoliative toxin causes skin sloughing, as seen in staphylococcal scalded skin syndrome heat-stable enterotoxin leads to food poisoning toxic shock syndrome toxin (TSST) leads to staphylococcal toxic shock syndrome Diseases S. aureus Associated Diseases Disease Clinical Presentation Comments Toxic shock syndrome Symptoms nausea and vomiting watery diarrhea Physical exam fever diffuse erythematous rash palm and sole desquamation hypotension Can be caused by leaving tampons in place for a long period of time stimulates toxic shock syndrome toxin-1 (TSST-1) release, penetrating the vaginal mucosa, and cross-linking the β region of the T-cell receptor to MHC class II leads to an overwhelming release ofIL-1 and IL-2IFN-γTNF-α Treatment source control removing the tampon or surgical suture that enabled the production of TSST-1 antibiotics the choice depends on drug sensitivity testing will not cure the disease but may help as it can eliminate TSST-1 producing S. aureus Staphylococcal skin syndrome Physical exam fever erythematous rash with skin sloughing Exfoliative toxin destroys keratinocyte attachments to the stratum granulosum Typically seen in newborns, children, and adults with renal insufficiency Gastroenteritis Symptoms nausea vomiting abdominal pain Physical exam watery diarrhea Staphylococci can produce exotoxin as it grows in food ingested pre-formed toxin causes intestinal peristalsis, resulting in nausea vomiting abdominal pain watery diarrhea Pneumonia Physical exam fevers chills Typically seen as a superinfection after an influenza upper respiratory infection results in a lobar consolidation and lung parenchymal cavitations Osteomyelitis Physical exam fever warm and swollen tissue over bone S. aureus spreads to the bone hematogenously Most common cause of osteomyelitis overall Acute endocarditis Symptoms chills myalgias Physical exam fever There is rapid vegetation growth on the heart valve, which can cause valvular destruction embolism to the brain leading to stroke with left-heart valvular involvement embolism to the lung with right-heart valvular involvement more common in intravenous drug users Septic arthritis Symptom joint pain Physical exam inflamed joint with decreased range of motion Caused by S. aureus invasion into the synovial membrane Joint aspiration can demonstrate yellow and turbid synovial fluid prominent amount of neutrophils (> 100,000 CFU/mL) positive Gram stain (gram-positive cocci in clusters) Skin infections Impetigo physical exam small vesicles or pustules that crust over into honey-colored lesions typically appear in the face and especially around the mouth Cellulitis physical exam fever the affected area is erythematous, warm, and tender to palpation Other skin infections include local abscess pus collection furuncles infection of a hair follicle carbuncles a cluster of furuncles Some skin infections can be caused by Streptococcus pyogenes or S. aureus; therefore, these skin infections should be treated with penicillinase-resistant penicillins (e.g., dicloxacillin) Staphylococci can produce exotoxin as it grows in food ingested pre-formed toxin causes intestinal peristalsis, resulting in nausea vomiting abdominal pain watery diarrhea Methicillin-Resistant S. aureus (MRSA) Introduction most staphylococci are penicillin resistant due to their penicillinase to combat this, a number of penicillinase-resistant penicillins were developed (e.g., methicillin and nafcillin) MRSA is a strain of S. aureus that has acquired resistance against penicillinase-resistant penicillins (thus being methicillin-resistant) due to altered penicillin-binding protein Epidemiology incidence typically appears in the hospital setting Microbiology transmission via health care workers Treatment medical vancomycin indication the drug of choice for MRSA linezolid indication can be used to treat vancomycin-resistant S. aureus (VRSA) Treatment Medical penicillinase-resistant penicillins indication drug of choice for organisms sensitive to these drugs medications nafcillin oxacillin dicloxacillin vancomycin indication MRSA linezolid indication VRSA