Staphylococci Flashcards
Diagnosis
Numerous Polymorphonuclear leukocytes (PMNs) (Neutrophils)
1) Gram Stain:
_Gram(+) Positive Cocci (grape-like clusters)
2) Culture: _Grow Best Aerobically (but are Facultative Anaerobes). _Clear Beta-Hemolysis @ Blood Agar (Completely Hemolyze RBCs) (Most strains, including Staph aureus) _Staph aureus: Produces White Colonies that turn Golden (aureus)
3) Catalase Test:
_All Staph are Catalase Positive
4) Coagulase:
_Converts Fibrinogen in Plasma to Fibrin Clot
_Staph aureus is Coagulase Positive!!
_CoNS: Coagulase Negative Staphs.
Staphylococcus aureus
Virulence Proteins
1) Protein A:
_Anti-Phagocytic Virulence Factor
_Binds to Fc portion of IgG, leaving Fab portion turned around,
_Preventing Opsonization and Phagocytosis
2) Clumping Factor (Clf):
_Adhesion
_Binds to Fibrinogen on Host cells
_This results in formation of a Fibrin Wall, which localizes the infection. Boil.
3) Fibronectin-Binding Proteins (FnBP):
_Adhesion
_Binds to Fibronectin on Host cells
4) Coagulase:
_Converts Fibrinogen in Plasma to Fibrin Clot
_Staph aureus is Coagulase Positive!!
_CoNS: Coagulase Negative Staphs.
5) Catalase:
_All Staph are Catalase Positive
Staph aureus
Toxins
1) Alpha-Toxin: _Staph aureus _Not secreted by CoNS _Pore-Forming Cytotoxin _Results in leakage of vital molecules and Cell Death. _Also inserts into and kills PMNs.
2) Exfoliatin:
_Staph aureus
_Binds to a specific cell membrane Ganglioside @ Epidermis of *Young Children
_Causes Intercellular Splitting of the Epidermis between the Stratum Spinosum and Stratum Granulosum
== Scalded Skin Syndrome
3) SuperAntigen Toxin (StaphSAgs):
_15 different ones
_Toxic Shock Syndrome Toxin (TSST-1) is one of them.
_Less than 10% of Staph aureus strains produce any StaphSAg.
_Are Strongly Mitogenic for T cells:
_SuperAntigen causes Cross-Linking between MHC and TCR,
_Resulting in Massive Cytokine Release.
4) Enterotoxin
_Staph aureus
_Cause Vomiting
_Heat-stable (even after boiling)
_Resistant to Gastric Acid and Jejunal Enzymes
_Thus, don’t leave moist food out at room or higher than room temp for hours!! Even if you cook it, the bacteria will be killed by the heat or in your GI, but the toxin will remain active!! There’s no treatment for the toxin, so just have to wait for it to pass.
Staph Epidemiology
Staph aureus @ Anterior Nares
10-30% of healthy ppl carry Staph aureus @ Nares
1) Community Infection:
Most Staph aureus infections acquired in the community are AUTOINFECTION (self-infection).
_Acne or broken skin, then touch your nose.
2) Hospital Infection:
Hospital Outbreaks caused by a single strain of Staph aureus are common.
_Source of Hospital Outbreak may be a patient with an overt or unapparent Staph infection (e.g., Decubitus Ulcer, aka Bed Sore) that is then spread directly to other patients on the hands of hospital personnel.
3) Food Poisoning:
Staph food poisoning is one of the Most Common food-borne illnesses worldwide.
_Moist Food, Rich (e.g. Red Meat, Poultry, Creamy Dishes)
_Fail to refrigerate for hours between preparation and serving; the staph are able to multiply and produce the Enterotoxin in the Food.
_Toxicity persists even if the Food is Subsequently cooked before eating because the Toxin is Heat-Resistant.
Clinical Capsule:
Staph Disease
Staph aureus infections are Acute, Aggressive, Locally Destructive, Purulent Lesions.
_Boil: Painful lump in skin that has a necrotic center and fibrous reactive shell.
_Organs: Lung, Kidney, Bone; also Focal and Destructive
_Those typically produce High Fever and Systemic Toxicity and may be Fatal in only a Few days.
_Subgroup (Less than 10%) of S aureus infections has manifestations produced by secreted toxins
_Symptoms include diarrhea, rash, skin desquamation, and multi-organ effects as in staphylococcal toxic shock syndrome (TSS).
_Ingestion of preformed staphylococcal enterotoxin causes a form of food poisoning in which vomiting begins in only a few hours.
Staph aureus Infection
1) Scalded Skin Syndrome:
_Due to Exfoliatin Toxin
_@ Neonates, Children under 5
_Occasionally in Adults, particularly immunocompromised.
2) Bullous Impetigo: _Due to Exfoliatin Toxin _@ Older Children _Localized, Blister-like lesions = a Localized form of Staph Scalded Skin Syndrome. _Skin abrasions or Acne can risk.
3) Furuncle (Boil): Localized, Superficial Skin infection. _Painful! _Necrotic center with Fibrous shell. (1) Furunculosis: _Often a complication of Acne Vulgaris (2) The Common Stye: _Infection @ Base of Eyelash _Usually Benign course
4) Carbuncle:
_Abscess in adjacent Subcutaneous tissues
_Most often @ Back of Neck
_Caused by Spread of infection from a Furuncle to development of one or more abscesses in adjacent subcutaneous tissues.
_Serious and may result in Bloodstream invasion (Bacteremia)
5) Toxic Shock Syndrome:
(1) Due to SuperAntigen TSST-1
(2) SuperAntigen results in massive release of cytokines TNF and IL-1
(3) Early Symptoms:
_High Fever
_Vomiting
_Diarrhea
_Sore Throat
_Muscle Pain
(4) Within 48 Hours:
_Severe Shock
_With Renal and Hepatic Damage
_Diffuse Erythematous (Red) Rash
_Desquamation of Palms and Soles
6) Food Poisoning:
_Ingestion of Staphylococcal Enterotoxin-Contaminated food
_Causes Acute Vomiting and Diarrhea within 1-5 Hours.
_No Fever
_Rapid Recovery, except sometimes in elderly and in ppl with another disease.
7) Deep Lesions:
_Due to Bacteremic Spread from a Skin lesion.
_@ Bones, Joints, Deep Organs, Soft Tissues, Surgical Wounds.
_Produces Localized, Destructive Abscesses
_Bacteremia and Endocarditis can Develop.
8) Osteomyelitis
_Staph aureus causes more than 90% of Acute Osteomyelitis in Children.
9) Endocarditis
_Severe Staph aureus infections, including Endocarditis, are particularly common in IV Drug users.
_Staphylococcal Pneumonia is usually Secondary to some Other insult to the lung.
Treatment of Staph aureus
Boils and Superficial Abscesses:
_Most Resolve Spontaneously
The more Extensive ones:
_Surgical Drainage and
_Antibiotics are both required.
Due to more than 80% Penicillin Resistance:
1) Penicillinase-Resistant Penicillins
(Methicillin, Nafcillin, Oxacillin) and
2) First-Generation Cephalosporins
\_\_\_\_\_\_ For MRSA Strains or Patients with Beta-Lactam Hypersensitivity: 1) Vancomycin 2) Clindamycin 3) Erythromycin
______
For MRSA and VRSA strains:
1) Daptomycin
______
Resistance:
_Most strains of Staph aureus are now Penicillin-resistant.
1) Penicillinase is mediated by Plasmid
2) New Penicillin-Binding Proteins (PBPs) are produced by MRSA strains.
3) MRSA is also resistant to other Penicillinase-Resistant Penicillins, such as Oxacillin.
Prevention of Staph aureus
In patients subject to Recurrent infection, such as Chronic Furunculosis:
_Controlling reinfection
_and Eliminating carrier state (if possible)
Dry-clean or Wash clothes and bedding at high temps (70 C or higher)
Chlorhexidine Soaps in Adults for showering and washing.
Chemoprophylaxis is Effective in Surgical procedures, such as hip and cardiac valve replacements.
Staph epidermidis
CoNS Disease
Coagulase Negative!!
Normal Flora!
@ Skin
@ Anterior Nares
@ Ear Canals
Secrete an extracellular polysaccharide slime BIOFILM glycocalyx that allows them to bind to devices, and protects them from immune system and antibiotics.
Epidemiology:
1) Hospital-Acquired Infections:
_Implanted Catheters and Prosthetic Devices.
2) Immunosuppressed or Neutropenic patients
3) Premature Infants.
4) Frequent contamination of specimens via Skin!
Staph saphrophyticus
CoNS Disease
Coagulase Negative!!!
Normal Flora!!
@ GI tract
Epidemiology:
_Gains access to Urinary Tract via GI tract
_Causes Community-Acquired infection in Women.
Manifestation:
= #2 Cause of Acute UTI among sexually-active women.
(E. coli is #1 cause)
Diagnosis and Treatment of CoNS
Diagnosis:
1) Gram Stain:
Gram(+) Positive Cocci in grape-like clusters
2) Culture
3) Coagulase Negative!!
4) Catalase Positive
Treatment:
1) Vancomycin: Staph epidermidis
(b/c resistant to multiple antibiotics)
2) Must also remove the catheter or prosthetic device!
Most CoNS are resistant to penicillin.
