Staphylococcus aureus - Microbiology

Snapshot

A 23-year-old woman presents to the emergency department with fever, chills, and watery diarrhea. Her symptoms began approximately 2 weeks ago. She started menses approximately 1 week ago. 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. (Toxic shock syndrome)
<table style="width: 100%; background-color: #ffffff; border: 0px solid #cccccc;" border="0" cellspacing="0">

<tbody>

<tr style="background-color: #f4f4f4;">

<td>Snapshot</td>

</tr>

<tr>

<td>

<ul>

<li>A</li>

</ul>

</td>

</tr>

<tr>

<td style="color: #000000; font-family: Arial, Helvetica, sans-serif; font-size: medium;" bgcolor="#F4F4F4">Introduction</td>

</tr>

<tr>

<td style="color: #000000; font-family: Arial, Helvetica, sans-serif; font-size: medium;" height="1" bgcolor="#ffffff">

<div>

<ul>

<li>Classification

<ul>

<li>Gram-positive cocci in clusters <a style="font-family: Arial, Helvetica, sans-serif;" title="This clinical image demonstrates gram-positive cocci in clusters, indicative of Staphylococcus aureus." href="https://upload.medbullets.com/topic/104183/images/250px-staphylococcus_aureus_gram.jpg"><img src="/images/camera.gif" alt="" /></a></li>

</ul>

</li>

<li>Microbiology

<ul>

<li style="font-family: Arial, Helvetica, sans-serif;">transmission

<ul style="font-family: Arial, Helvetica, sans-serif;">

<li>contaminated foods

<ul>

<li>custards</li>

<li>mayonnaise/potato salad</li>

<li>canned meats</li>

</ul>

</li>

</ul>

</li>

<li style="font-family: Arial, Helvetica, sans-serif;">properties

<ul>

<li>facultative anaerobes</li>

<li>catalase-positive

<ul style="font-family: Arial, Helvetica, sans-serif;">

<li>neutralizes its own H2O2, which causes the human's phagocytes to not have the ability to produce reactive oxygen species to combat infection in patient's with chronic granulomatous disease <a href="/immunology/105009/chronic-granulomatous-disease"><img src="/images/topic.png" alt="" /></a></li>

</ul>

</li>

<li>coagulase positive

<ul style="font-family: Arial, Helvetica, sans-serif;">

<li>coagulase activates prothrombin, leading to clotting

<ul>

<li>leads to fibrin formation around this organism</li>

</ul>

</li>

<li>differentiates S. aureus from S. epidermidis and S. saprophytic</li>

</ul>

</li>

<li>β-hemolytic

<ul style="font-family: Arial, Helvetica, sans-serif;">

<li>complete hemolysis of red blood cells on an agar plate</li>

</ul>

</li>

<li>appears gold in sheep blood agar</li>

<li>protein A <a style="font-size: medium;" title="question" href="#101563"><img src="/images/question_step_1.png" alt="" /></a>

<ul style="font-family: Arial, Helvetica, sans-serif;">

<li>binds to the Fc region of the IgG antibody

<ul>

<li>this presents opsonization and phagocytosis</li>

</ul>

</li>

</ul>

</li>

<li style="font-family: Arial, Helvetica, sans-serif;">hemolysins

<ul style="font-family: Arial, Helvetica, sans-serif;">

<li>damages red blood cells, platelets, neutrophils, and macrophages</li>

</ul>

</li>

<li style="font-family: Arial, Helvetica, sans-serif;">leukocidins

<ul style="font-family: Arial, Helvetica, sans-serif;">

<li>damages white blood cells</li>

</ul>

</li>

<li>penicillinase

<ul style="font-family: Arial, Helvetica, sans-serif;">

<li>a secreted form of β-lactamase, which makes S. aureus resistant to penicillins</li>

</ul>

</li>

<li style="font-family: Arial, Helvetica, sans-serif;">toxins

<ul>

<li>exfoliative toxin

<ul>

<li>causes skin sloughing, as seen in staphylococcal scalded skin syndrome</li>

</ul>

</li>

<li>heat stable enterotoxin

<ul style="font-family: Arial, Helvetica, sans-serif;">

<li>leads to food poisoning</li>

</ul>

</li>

<li>toxic shock syndrome toxin (TSST) <a style="font-size: medium;" title="question" href="#109726"><img src="/images/question_step_1.png" alt="" /></a>

<ul style="font-family: Arial, Helvetica, sans-serif;">

<li>leads to staphylococcal toxic shock syndrome</li>

</ul>

</li>

</ul>

</li>

</ul>

</li>

</ul>

</li>

</ul>

</div>

</td>

</tr>

<tr>

<td style="color: #000000; font-family: Arial, Helvetica, sans-serif; font-size: medium;" bgcolor="#F4F4F4">Diseases</td>

</tr>

<tr>

<td> </td>

</tr>

<tr>

<td>

<table style="margin: 0px auto; padding: 0px; vertical-align: baseline; border-spacing: 0px; color: #000000; font-family: Arial, Helvetica-Neue, Helvetica, sans-serif; font-size: 16px; width: 613px; border-image: initial !important; border: 1px solid #f4f4f4;" border="1" cellspacing="0" align="center">

<tbody style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">

<tr style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; background-color: #d4f2cd;">

<td style="margin: 0px; padding: 1px; vertical-align: middle; font-variant-numeric: normal; font-variant-east-asian: normal; font-stretch: normal; line-height: 1.3; text-align: center; width: 95%; border-image: initial !important; border: 1px solid #f4f4f4;" colspan="3">S. aureus Associated Diseases</td>

</tr>

<tr style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; text-align: center; background-color: #f4f4f4;">

<td style="margin: 0px; padding: 1px; vertical-align: middle; font-variant-numeric: normal; font-variant-east-asian: normal; font-stretch: normal; line-height: 1.3; width: 110px; border: 1px solid #f4f4f4 !important;">Disease </td>

<td style="margin: 0px; padding: 1px; vertical-align: middle; font-variant-numeric: normal; font-variant-east-asian: normal; font-stretch: normal; line-height: 1.3; width: 137px; border: 1px solid #f4f4f4 !important;">Clinical Presentation </td>

<td style="margin: 0px; padding: 1px; vertical-align: middle; font-variant-numeric: normal; font-variant-east-asian: normal; font-stretch: normal; line-height: 1.3; width: 139px; border: 1px solid #f4f4f4 !important;">Comments</td>

</tr>

<tr style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">

<td style="margin: 0px; padding: 1px; vertical-align: middle; font-variant-numeric: normal; font-variant-east-asian: normal; font-stretch: normal; line-height: 1.3; font-family: Arial, Helvetica-Neue, Helvetica, sans-serif; border: 1px solid #f4f4f4 !important;">Toxic shock syndrome</td>

<td style="margin: 0px; padding: 1px; vertical-align: middle; font-variant-numeric: normal; font-variant-east-asian: normal; font-stretch: normal; line-height: 1.3; font-family: Arial, Helvetica-Neue, Helvetica, sans-serif; border: 1px solid #f4f4f4 !important;" valign="middle">

<ul style="margin: 16px 0px; padding: 0px 0px 0px 20px; border: 0px; vertical-align: baseline; list-style-position: initial; list-style-image: initial;">

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">Symptoms 

<ul style="margin: 0px; padding: 0px 0px 0px 20px; border: 0px; vertical-align: baseline; list-style-position: initial; list-style-image: initial;">

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">nausea and vomiting</li>

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">watery diarrhea</li>

</ul>

</li>

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">Physical exam 

<ul>

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">fever</li>

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">diffuse erythematous rash</li>

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">palm and sole desquamation</li>

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">hypotension</li>

</ul>

</li>

</ul>

</td>

<td style="margin: 0px; padding: 1px; vertical-align: middle; font-variant-numeric: normal; font-variant-east-asian: normal; font-stretch: normal; line-height: 1.3; font-family: Arial, Helvetica-Neue, Helvetica, sans-serif; border: 1px solid #f4f4f4 !important;" valign="middle">

<ul style="margin: 16px 0px; padding: 0px 0px 0px 20px; border: 0px; vertical-align: baseline; list-style-position: initial; list-style-image: initial;">

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">Can be caused by leaving tampons in place for a long period of time 

<ul>

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">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 

<ul>

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">leads to an overwhelming release of 

<ul>

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">IL-1 and IL-2</li>

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">IFN-γ</li>

</ul>

<ul>

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">TNF-α</li>

</ul>

</li>

</ul>

</li>

</ul>

</li>

<li>Treatment 

<ul>

<li>source control 

<ul>

<li>removing the tampon or surgical suture that enabled the production of TSST-1</li>

</ul>

</li>

<li>antibiotics 

<ul>

<li>the choice depends on drug sensitivity testing</li>

<li>will not cure the disease but may help as it can eliminate TSST-1 producing S. aureus</li>

</ul>

</li>

</ul>

</li>

</ul>

</td>

</tr>

<tr style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">

<td style="margin: 0px; padding: 1px; vertical-align: middle; font-variant-numeric: normal; font-variant-east-asian: normal; font-stretch: normal; line-height: 1.3; font-family: Arial, Helvetica-Neue, Helvetica, sans-serif; border: 1px solid #f4f4f4 !important;">Staphylococcal skin syndrome</td>

<td style="margin: 0px; padding: 1px; vertical-align: middle; font-variant-numeric: normal; font-variant-east-asian: normal; font-stretch: normal; line-height: 1.3; font-family: Arial, Helvetica-Neue, Helvetica, sans-serif; border: 1px solid #f4f4f4 !important;" valign="middle">

<div> </div>

<ul style="margin: 0px; padding: 0px 0px 0px 20px; border: 0px; vertical-align: baseline; list-style-position: initial; list-style-image: initial;">

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">Physical exam 

<ul style="margin: 0px; padding: 0px 0px 0px 20px; border: 0px; vertical-align: baseline; list-style-position: initial; list-style-image: initial;">

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">fever</li>

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">erythematous rash with skin sloughing</li>

</ul>

</li>

</ul>

</td>

<td style="margin: 0px; padding: 1px; vertical-align: middle; font-variant-numeric: normal; font-variant-east-asian: normal; font-stretch: normal; line-height: 1.3; font-family: Arial, Helvetica-Neue, Helvetica, sans-serif; border: 1px solid #f4f4f4 !important;" valign="middle">

<ul style="margin: 16px 0px; padding: 0px 0px 0px 20px; border: 0px; vertical-align: baseline; list-style-position: initial; list-style-image: initial;">

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">Exfoliative toxin destroys keratinocyte attachments to the stratum granulosum</li>

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">Typically seen in newborns, children, and adults with renal insufficiency</li>

</ul>

</td>

</tr>

<tr style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">

<td style="margin: 0px; padding: 1px; vertical-align: middle; font-variant-numeric: normal; font-variant-east-asian: normal; font-stretch: normal; line-height: 1.3; font-family: Arial, Helvetica-Neue, Helvetica, sans-serif; border: 1px solid #f4f4f4 !important;">Gastroenteritis </td>

<td style="margin: 0px; padding: 1px; vertical-align: middle; font-variant-numeric: normal; font-variant-east-asian: normal; font-stretch: normal; line-height: 1.3; font-family: Arial, Helvetica-Neue, Helvetica, sans-serif; border: 1px solid #f4f4f4 !important;" valign="middle">

<ul style="margin: 16px 0px; padding: 0px 0px 0px 20px; border: 0px; vertical-align: baseline; list-style-position: initial; list-style-image: initial;">

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">Symptoms 

<ul style="margin: 0px; padding: 0px 0px 0px 20px; border: 0px; vertical-align: baseline; list-style-position: initial; list-style-image: initial;">

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">nausea</li>

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">vomiting</li>

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">abdominal pain</li>

</ul>

</li>

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">Physical exam 

<ul style="margin: 0px; padding: 0px 0px 0px 20px; border: 0px; vertical-align: baseline; list-style-position: initial; list-style-image: initial;">

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">watery diarrhea</li>

</ul>

</li>

</ul>

</td>

<td style="margin: 0px; padding: 1px; vertical-align: middle; font-variant-numeric: normal; font-variant-east-asian: normal; font-stretch: normal; line-height: 1.3; font-family: Arial, Helvetica-Neue, Helvetica, sans-serif; border: 1px solid #f4f4f4 !important;" valign="middle">

<div style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">

<ul style="margin: 16px 0px; padding: 0px 0px 0px 20px; border: 0px; vertical-align: baseline; list-style-position: initial; list-style-image: initial;">

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">Staphylococci can produce exotoxin as it grows in food 

<ul>

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">pre-formed toxin because ingested, which causes intestinal peristalsis, resulting in 

<ul>

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">nausea</li>

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">vomiting</li>

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">abdominal pain</li>

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">watery diarrhea</li>

</ul>

</li>

</ul>

</li>

</ul>

</div>

</td>

</tr>

<tr style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">

<td style="margin: 0px; padding: 1px; vertical-align: middle; font-variant-numeric: normal; font-variant-east-asian: normal; font-stretch: normal; line-height: 1.3; font-family: Arial, Helvetica-Neue, Helvetica, sans-serif; border: 1px solid #f4f4f4 !important;" align="left" valign="middle">Pneumonia</td>

<td style="margin: 0px; padding: 1px; vertical-align: middle; font-variant-numeric: normal; font-variant-east-asian: normal; font-stretch: normal; line-height: 1.3; font-family: Arial, Helvetica-Neue, Helvetica, sans-serif; border: 1px solid #f4f4f4 !important;" align="left" valign="middle">

<ul style="margin: 16px 0px; padding: 0px 0px 0px 20px; border: 0px; vertical-align: baseline; list-style-position: initial; list-style-image: initial;">

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">Physical exam 

<ul style="margin: 0px; padding: 0px 0px 0px 20px; border: 0px; vertical-align: baseline; list-style-position: initial; list-style-image: initial;">

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">fevers</li>

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">chills</li>

</ul>

</li>

</ul>

</td>

<td style="margin: 0px; padding: 1px; vertical-align: middle; font-variant-numeric: normal; font-variant-east-asian: normal; font-stretch: normal; line-height: 1.3; font-family: Arial, Helvetica-Neue, Helvetica, sans-serif; border: 1px solid #f4f4f4 !important;" align="left" valign="middle">

<ul style="margin: 16px 0px; padding: 0px 0px 0px 20px; border: 0px; vertical-align: baseline; list-style-position: initial; list-style-image: initial;">

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">Typically seen as a superinfection after an influenza upper respiratory infection

<ul>

<li style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline;">results in a lobar consolidation and lung parenchymal cavitations</li>

</ul>

</li>

</ul>

</td>

</tr>

<tr>

<td align="left" valign="middle">Osteomyelitis</td>

<td align="left" valign="middle">

<ul>

<li>Physical exam

<ul>

<li>fever</li>

<li>warm and swollen tissue over bone</li>

</ul>

</li>

</ul>

</td>

<td align="left" valign="middle">

<ul>

<li>S. aureus spreads to the bone hematogenously</li>

<li>Most common cause of osteomyelitis overall <a style="font-size: medium;" title="question" href="#211041"><img src="/images/question_sae.png" alt="" /></a></li>

</ul>

</td>

</tr>

<tr>

<td align="left" valign="middle">Acute endocarditis</td>

<td align="left" valign="middle">

<ul>

<li>Symptoms

<ul>

<li>chills</li>

<li>myalgias</li>

</ul>

</li>

<li>Physical exam

<ul>

<li>fever</li>

</ul>

</li>

</ul>

</td>

<td align="left" valign="middle">

<ul>

<li>There is rapid vegetation growth on the heart valve, which can cause

<ul>

<li>valvular destruction</li>

<li>embolism to the brain leading to stroke

<ul>

<li>with left-heart valvular involvement</li>

</ul>

</li>

<li>embolism to the lung

<ul>

<li>with right-heart valvular involvement

<ul>

<li>more common in intravenous drug users</li>

</ul>

</li>

</ul>

</li>

</ul>

</li>

</ul>

</td>

</tr>

<tr align="left" valign="middle">

<td>Septic arthritis</td>

<td>

<ul>

<li>Symptom

<ul>

<li>joint pain</li>

</ul>

</li>

<li>Physical exam

<ul>

<li>inflamed joint with decreased range of motion</li>

</ul>

</li>

</ul>

</td>

<td align="left" valign="middle">

<ul>

<li>Caused by S. aureus invasion into the synovial membrane</li>

<li>Joint aspiration demonstrates

<ul>

<li>yellow and turbid synovial fluid</li>

<li>prominent amount of neutrophils (>100,000)</li>

<li>positive Gram stain (gram-positive cocci in clusters)</li>

</ul>

</li>

</ul>

</td>

</tr>

<tr align="left" valign="middle">

<td>Skin infections</td>

<td>

<ul>

<li>Impetigo <a style="font-size: medium;" title="question" href="#109288"><img src="/images/question_step_1.png" alt="" /></a>

<ul>

<li>physical exam

<ul>

<li>small vesicles or pustules that crust over into honey-colored lesions

<ul>

<li>typically appear in the face and especially around the mouth</li>

</ul>

</li>

</ul>

</li>

</ul>

</li>

<li>Cellulitis

<ul>

<li>physical exam

<ul>

<li>fever</li>

<li>the affected area is erythematous, warm, and tender to palpation</li>

</ul>

</li>

</ul>

</li>

<li>Other skin infections include

<ul>

<li>local abscess

<ul>

<li>pus collection</li>

</ul>

</li>

<li>furuncles

<ul>

<li>infection of a hair follicle</li>

</ul>

</li>

<li>carbuncles

<ul>

<li>a cluster of furuncles</li>

</ul>

</li>

</ul>

</li>

</ul>

</td>

<td>

<ul>

<li>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)</li>

</ul>

</td>

</tr>

</tbody>

</table>

</td>

</tr>

<tr>

<td> </td>

</tr>

<tr style="background-color: #f4f4f4;">

<td>Methicillin-Resistant S. aureus (MRSA)</td>

</tr>

<tr>

<td>

<ul>

<li>Introduction

<ul>

<li>most staphylococci are penicillin resistant due to their penicillinase

<ul>

<li>to combat this, a number of penicillinase-resistant penicillins were developed (e.g., methicillin and nafcillin)</li>

</ul>

</li>

<li>MRSA is a strain of S. aureus that has acquired resistance against penicillinase-resistant penicillins (thus being methicillin-resistant)

<ul>

<li>due to altered penicillin-binding protein</li>

</ul>

</li>

</ul>

</li>

<li>Epidemiology

<ul>

<li>incidence

<ul>

<li>typically appears in the hospital setting <a style="font-size: medium;" title="question" href="#101540"><img src="/images/question_step_1.png" alt="" /></a></li>

</ul>

</li>

</ul>

</li>

<li>Microbiology

<ul>

<li>transmission

<ul>

<li>via health care workers</li>

</ul>

</li>

</ul>

</li>

<li>Treatment

<ul>

<li>medical

<ul>

<li>vancomycin

<ul>

<li>indication

<ul>

<li>the drug of choice for MRSA</li>

</ul>

</li>

</ul>

</li>

<li>linezolid

<ul>

<li>indication

<ul>

<li>can be used to treat vancomycin-resistant S. aureus (VRSA)</li>

</ul>

</li>

</ul>

</li>

</ul>

</li>

</ul>

</li>

</ul>

</td>

</tr>

<tr>

<td style="color: #000000; font-family: Arial, Helvetica, sans-serif; font-size: medium;" bgcolor="#F4F4F4">Treatment</td>

</tr>

<tr>

<td>

<ul>

<li>Medical

<ul>

<li>penicillinase-resistant penicillins

<ul>

<li>indication

<ul>

<li>drug of choice for organisms sensitive to these drugs</li>

</ul>

</li>

<li>medications

<ul>

<li>nafcillin</li>

<li>oxacillin</li>

<li>dicloxacillin</li>

</ul>

</li>

</ul>

</li>

<li>vancomycin

<ul>

<li>indication

<ul>

<li>MRSA</li>

</ul>

</li>

</ul>

</li>

<li>linezolid

<ul>

<li>indication

<ul>

<li>VRSA</li>

</ul>

</li>

</ul>

</li>

</ul>

</li>

</ul>

</td>

</tr>

</tbody>

</table>

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 of IL-1 and IL-2 IFN-γ TNF-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)

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

Blood, Plasma, Serum	Reference Range
ALT	8-20 U/L
Amylase, serum	25-125 U/L
AST	8-20 U/L
Bilirubin, serum (adult) Total // Direct	0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca²⁺)	8.4-10.2 mg/dL
Cholesterol, serum	Rec: < 200 mg/dL
Cortisol, serum	0800 h: 5-23 μg/dL //1600 h: 3-15 μg/dL 2000 h: ≤ 50% of 0800 h
Creatine kinase, serum	Male: 25-90 U/L Female: 10-70 U/L
Creatinine, serum	0.6-1.2 mg/dL
Electrolytes, serum
Sodium (Na⁺)	136-145 mEq/L
Chloride (Cl^-)	95-105 mEq/L
Potassium (K⁺)	3.5-5.0 mEq/L
Bicarbonate (HCO₃^-)	22-28 mEq/L
Magnesium (Mg²⁺)	1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)
24-28 wks // 32-36 wks	30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks	40-220 ng/mL // 80-350 ng/mL
Ferritin, serum	Male: 15-200 ng/mL Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma	Male: 4-25 mIU/mL Female: premenopause: 4-30 mIU/mL midcycle peak: 10-90 mIU/mL postmenopause: 40-250
pH	7.35-7.45
PCO₂	33-45 mmHg
PO₂	75-105 mmHg
Glucose, serum	Fasting: 70-110 mg/dL 2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation	Fasting: <5 ng/mL Provocative stimuli: > 7ng/mL
Immunoglobulins, serum
IgA	76-390 mg/dL
IgE	0-380 IU/mL
IgG	650-1500 mg/dL
IgM	40-345 mg/dL
Iron	50-170 μg/dL
Lactate dehydrogenase, serum	45-90 U/L
Luteinizing hormone, serum/plasma	Male: 6-23 mIU/mL Female: follicular phase: 5-30 mIU/mL midcycle: 75-150 mIU/mL postmenopause 30-200 mIU/mL
Osmolality, serum	275-295 mOsmol/kd H₂O
Parathyroid hormone, serume, N-terminal	230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C)	20-70 U/L
Phosphorus (inorganic), serum	3.0-4.5 mg/dL
Prolactin, serum (hPRL)	< 20 ng/mL
Proteins, serum

Hematologic	Reference Range
Bleeding time	2-7 minutes
Erythrocyte count	Male: 4.3-5.9 million/mm³ Female: 3.5-5.5 million mm³
Erythrocyte sedimentation rate (Westergren)	Male: 0-15 mm/h Female: 0-20 mm/h
Hematocrit	Male: 41%-53% Female: 36%-46%
Hemoglobin A1c	≤ 6 %
Hemoglobin, blood	Male: 13.5-17.5 g/dL Female: 12.0-16.0 g/dL
Hemoglobin, plasma	1-4 mg/dL
Leukocyte count and differential
Leukocyte count	4,500-11,000/mm³
Segmented neutrophils	54%-62%
Bands	3%-5%
Eosinophils	1%-3%
Basophils	0%-0.75%
Lymphocytes	25%-33%
Monocytes	3%-7%
Mean corpuscular hemoglobin	25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration	31%-36% Hb/cell
Mean corpuscular volume	80-100 μm³
Partial thromboplastin time (activated)	25-40 seconds
Platelet count	150,000-400,000/mm³
Prothrombin time	11-15 seconds
Reticulocyte count	0.5%-1.5% of red cells
Thrombin time	< 2 seconds deviation from control
Volume
Plasma	Male: 25-43 mL/kg Female: 28-45 mL/kg
Red cell	Male: 20-36 mL/kg Female: 19-31 mL/kg

Cerebrospinal Fluid	Reference Range
Cell count	0-5/mm³
Chloride	118-132 mEq/L
Gamma globulin	3%-12% total proteins
Glucose	40-70 mg/dL
Pressure	70-180 mm H₂O
Proteins, total	< 40 mg/dL

Sweat	Reference Range
Chloride	0-35 mmol/L
Urine
Calcium	100-300 mg/24 h
Chloride	Varies with intake
Creatinine clearance	Male: 97-137 mL/min Female: 88-128 mL/min
Estriol, total (in pregnancy)
30 wks	6-18 mg/24 h
35 wks	9-28 mg/24 h
40 wks	13-42 mg/24 h
17-Hydroxycorticosteroids	Male: 3.0-10.0 mg/24 h Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total	Male: 8-20 mg/24 h Female: 6-15 mg/24 h
Osmolality	50-1400 mOsmol/kg H₂O
Oxalate	8-40 μg/mL
Potassium	Varies with diet
Proteins, total	< 150 mg/24 h
Sodium	Varies with diet
Uric acid	Varies with diet
Body Mass Index (BMI)	Adult: 19-25 kg/m²