Staphylococcus aureus infection encompasses a broad spectrum of diseases affecting the skin, soft tissues, bones, joints, heart, and other organs. Each manifestation is associated with risk factors, clinical presentation, and diagnostic findings.
Staphylococcus aureus, which has emerged as a major pathogen in the past decades , can infect the skin and soft tissues, bones, joints, lungs, endocardium, bloodstream, and other organs . Normally, this bacterium colonizes about 30% of humans . Epidemiology reports note that in addition to community-associated infections, this pathogen is also responsible for many health-care associated infections related to medical devices . S. aureus is transmitted by contact with an infected person or contaminated objects, and inhalation of droplets. Risk factors for this infection are chronic lung diseases, diabetes mellitus, chronic skin diseases, influenza infection, malignancies, surgeries, immunosuppressant use, intravenous drug use, and HIV infection.
S. aureus infection consists of diseases that range from benign to life-threatening  and their manifestations are described below.
Skin and soft tissue infections (SSTIs) include impetigo, cellulitis, and abscesses such as folliculitis, furuncles, and carbuncles. Very importantly, SSTIs can disseminate via the bloodstream and cause septicemia  and spread to muscles  and other organs .
Osteomyelitis and septic arthritis are two of the most serious S.aureus infections. Some of the features of osteomyelitis are fever, bone pain, and limping while septic arthritis features include fever and warm, erythematous, and painful joints with restricted motion .
Symptoms of infective endocarditis (IE), which can affect heart valves and the endocardium, are fever, malaise, chills, and sweating. Moreover, patients may exhibit new onset of murmur or the worsening of a preexisting one, Osler nodes, Janeway lesions, Roths spots, subungual hemorrhages, and others.
One of the most ominous S.aureus infections is known as toxic shock syndrome (TSS). The CDC criteria for the diagnosis of TSS are 1) fever, 2) shock that is refractory to resuscitation, 3) diffuse macular rash, and 4) involvement of at least 3 organ systems . Patients are likely to exhibit an altered mental status, vaginal hyperemia, skin manifestations, etc.
When evaluating a suspected S. aureus infection, the clinician should elicit the individual's personal history and risk factors, and perform a thorough physical exam and the appropriate studies.
With regards to skin infections, inspection is usually sufficient to confirm the diagnosis although some cases will warrant aspiration and culture of the purulent material . Also, ultrasonography may help in the diagnosis of soft tissue infections .
Osteomyelitis is typically associated with peripheral leukocytosis and increased levels of erythrocyte sedimentation rate (ESR) and serum C-reactive protein (CRP) . Additionally, patients may have positive blood cultures, but if not, bone biopsy and culture should be performed . Very importantly, imaging studies such as radiography, magnetic resonance imaging (MRI), and/or other modalities are obtained.
Septic arthritis is diagnosed based on elevated leukocytes in synovial fluid . Moreover, the aspirated fluid is also sent for a culture and a Gram stain and radiography and/or other imaging tools are used in the workup.
To assess for S. aureus pneumonia, blood cultures are not reliable and therefore, a sample from the respiratory tract should be obtained. Additionally, chest radiography findings vary depending on whether the staphylococcal pneumonia is a primary or secondary infection. For example, primary infection demonstrates unilateral consolidation whereas secondary reveals bilateral involvement. Note that chest X-rays will reveal disease progression, which usually occurs rapidly.
Diseases such as IE and TSS are complicated and require an extensive workup. For example, patients diagnosed with IE should meet modified Duke criteria that consist of history and physical findings as well as blood culture and echocardiography results . Finally, TSS requires a careful assessment of the history, physical exam, and the appropriate studies.
- Gram-Positive Bacteria
The effect of propionate on other Gram-positive bacteria was also investigated. Results Of the three SCFAs, propionate most potently inhibited the growth of MRSA USA300, inhibiting its growth in a dose-dependent manner. [s-space.snu.ac.kr]
Gram-positive bacteria acquire resistance to beta-lactam antibiotics through the production of a protein called PBP2a, which is able to avoid the inhibitory effects of the antibiotics. [bcm.edu]
However, some infections involve other transmission methods. Etiology Staphylococcus aureus is Gram-positive bacteria (stain purple by Gram stain) that are cocci-shaped and tend to be arranged in clusters that are described as “grape-like.” [ncbi.nlm.nih.gov]
Linezolid is a bacteriostatic oxazolidin that has high oral bioavailability and inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit in Gram-positive bacteria and mycobacterial species ( 122, 123 ). [cjasn.asnjournals.org]
Telavancin versus standard therapy for treatment of complicated skin and skin structure infections caused by gram-positive bacteria: FAST 2 study. Antimicrob Agents Chemother 2006;50:862–867. [jkma.org]
- Gram-Positive Coccus
Abstract Staphylococcus aureus is a Gram-positive coccus that interacts with human hosts on a spectrum from quiet commensal to deadly pathogen. [ncbi.nlm.nih.gov]
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