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Transcript of Staphylococci
Coagulase negative staph
S. aureus produces 3 types of toxin:
predisposing factors include:
chronic skin conditions (e.g., eczema)
injections (e.g., in diabetes, injection drug use)
X-rays may be normal for up to 14 days
99mTc-phosphonate scanning detects early infection
Nosocomial S. aureus pulmonary infections - seen in intubated patients
Community-acquired respiratory tract infections usually follow viral infections—most commonly influenza.
Bacteremia and Endocarditis
Transesophageal echocardiography - more invasive
Transthoracic echocardiography - less sensitive
Toxin-producing S. aureus into food is colonized by food handlers
Toxin is elaborated in food as custards, potato salad, or processed meats.
Toxin is heat stable
Survives conditions that kill the bacteria.
Ingestion of preformed toxin
Incubation period is short (1–6 h).
The skin is fragile and tender, with thin-walled, fluid-filled bullae
Gentle pressure results in rupture of the lesions, leaving denuded underlying skin (Nikolsky's sign)
Coagulase - Negative Staphylococcus
Elaborates the extracellular polysaccharide (glycocalyx or slime) and
Forms the biofilm on the device surface.
Biofilm acts as a barrier - protects bacteria from immunity as well as from antibiotics
Provides a suitable environment for bacterial survival.
only <5% of isolated strains are susceptible
Methicillin resistant (MRSA):
Gram Positive Cocci
Staphyle - bunch of grapes
Kokkos - berries
Most common cause of surgical wound infections.
Enzymes: Serine Proteases, Hyaluronidases, Thermonucleases, Lipases. They facilitate survival and local spread.
Forms grapelike clusters on Gram's stain
Non - motile
Coagulase + (converts fibrinogen to fibrin)
Is a part of the normal human flora;
Protein A, unique to S. aureus, , binds the Fc portion of IgG - prevents opsonization and phagocytosis by PMNs.
Skin and Soft Tissue Infections
Toxic Shock Syndrome Toxin 1
Toxic Shock Syndrome Toxin 1 (TSST-1)
use of a highly absorbent tampon that had recently been introduced to the market.
The result is:
Massive release of inflammatory cytokines: interferon alfa , IL-1, IL-6, TNF-alfa.
Multisystem failure and shock;
1. Fever: temperature of 38.9°C (102°F)
2. Systolic blood pressure of 90 mmHg,
or orthostatic hypotension
3. Diffuse macular rash, with desquamation 1–2 weeks after onset
4. Multisystem involvement:
Hepatic: bilirubin or aminotransferase levels 2 times normal,
Hematologic: platelet count < 100,000/L,
Renal: blood urea nitrogen or serum creatinine level 2 times the normal upper limit
Mucous membranes: vaginal, oropharyngeal, or conjunctival hyperemia,
Gastrointestinal: vomiting, diarrhea
Muscular: severe myalgias, serum creatine phosphokinase level 2 times the upper limit,
Central nervous system: disorientation, alteration in consciousness
5.Negative cultures for organisms other than S. aureus
Supportive therapy with reversal of hypotension is the mainstay of therapy for TSS.
Treatment - Supportive
The toxin stimulates vomiting center of the brain and peristaltic activity
Carbuncles - even more severe and painful, resulting from the coalescence of other lesions. extend to a deeper layer of the subcutaneous tissue.
Folliculitis is a superficial infection that involves the hair follicles, with a central area of purulence (pus) surrounded by erythema.
Furuncles (boils) are Larger, painful lesions - occurs at hairy, moist regions of the body.
Osteomyelitis in Children
S. aureus is among the most common causes
long bones - most commonly
Inability to bear weight.
May be clinically occult: chronic back pain and low-grade fever
White blood cell count is elevated
Erythrocyte sedimentation rate is elevated.
Blood cultures are positive in 50% of cases.
MRI - The most sensitive for radiological diagnosis
S. Aureus - most common cause of septic arthritis
May be associated with extensive joint destruction.
Intense pain on motion of the affected joint
IV drug users.
Risk in Adults:
Diabetic ulcers, surgery, trauma.
Bone biopsies for culture - MOST ACCURATE
S. aureus - most common cause of epidural abscess
Can result in neurologic compromise
Surgical intervention is a medical emergency.
Aspiration of the joint:
Gram-positive cocci in clusters.
The most commonly involved joints include the knees, shoulders, hips, and phalanges
Mri - most sensitive radiologic test
Best Initial Test: Chest X- ray
Most accurate test: Sputum Gram's stain and culture
S. aureus - leading cause of endocarditis. (25–35% of cases)
Mortality rate is 20 to 40%
Complications: cardiac valvular insufficiency, peripheral emboli, metastatic seeding, and CNS involvement - embolic strokes
New or changing cardiac murmur
Cutaneous evidence, such as vasculitic lesions
Right- or left-sided embolic disease;
History suggesting a risk
Hemodynamic changes — beginning with respiratory alkalosis, hypotension and fever.
Duke's criteria For endocarditis
Positive blood cultures
Valvular vegetations on Echo
Fever >38 C
IV drug abuse
DEFINITE Endocarditis: 1major + 3minor
1major +1 minor
Toxic clinical appearance
Pleuritic chest pain
Production of purulent (sometimes bloody) sputum
NO HISTORY OF VALVE DAMAGE
suspect in every patient with:
Diagnosis: positive blood cultures
tricuspid valvular endocarditis - in IV drug users
Previously affected valve.
Patients tend to be older
Prognosis is worse
More acute presentation
Successful Management - removal of the device.
S. aureus device-related infections
best initial test:
Blood culture 95-99% sensitive
The most abundant on the normal skin
Normal flora of the oropharynx and vagina.
Causes Urinary Tract Infections (UTI).
The Most common cause of prosthetic-device infections
Since these organisms are present on the skin, they often contaminate cultures.
Multiple isolations of the same strain is suggestive of true bacteremia
Evidence of local infection (erythema or purulent drainage at the IV catheter site)
Systemic signs of sepsis
Penicillin Allergic Patients:
1. Harrison's Principles of Internal Medicine, 18Th Edition
2. Merck Manual of Clinical Diagnosis, 19Th Edition
3. Master the Boards USMLE Step 2 CK, 3rd Edition
Sites of colonization:
In early 1980s an outbreak of Toxic Shock Syndrome occurred among young, healthy women.
Causes Staphylococcal Scalded-Skin Syndrome (SSSS)
Toxins disrupt the desmosomes
Epidermis splits at the granular layer
Superficial desquamation is typical to this illness
SSSS most often affects newborns and children.