Staphylococcus : Staphylococcus D.Surendra gollapudi Slide 2: Genus: Staphylococcus
Species: aureus, epidermidis
GENERAL CONCEPTS: The staphylococci are divided in two groups based on the presence or absence of the enzyme coagulase. This enzyme converts fibrinogen into fibrin, causing blood plasma to clot. The species called S. aureus is coagulase-positive while S. epidermidis (and other "non-pathogens") is coagulase-negative.
Typically, staphylococci are opportunistic pathogens or saprophytes. Slide 3: DISTINCTIVE PROPERTIES: Staphylococci are Gram-positive cocci usually arranged in clusters like a bunch of grapes. This appearance is due to the fact that staphylococci divide along two separate planes.
The morphologically similar streptococci can be differentiated from staphylococci by testing for the enzyme catalase; staphylococci possess this enzyme while streptococci do not. Slide 4: Staphylococci possess both group specific and type specific antigens: 90% of S. aureus isolates have protein A. This substance is capable of binding the Fc portion of immunoglobulin IgG. This property helps the bacterium escape the potentially lethal effects of immunoglobulin action and also serves as the basis for some serological tests (coagglutination).
Toxins produced by S. aureus include: hemolysins, leukocidins, enterotoxin, exfoliative toxin and toxic shock syndrome (TSS) toxin.
Extracellular enzymes produced by S. aureus include: coagulase, fibrinolysin, DNAse, lipases and hyaluronidase. Gram staining and transmission electron microscopy of clinical samples of Staphylococcus aureus : Gram staining and transmission electron microscopy of clinical samples of Staphylococcus aureus Slide 6: PATHOGENESIS: Coagulase negative strains of Staphylococcus are generally non-invasive. Under certain conditions, however, they may cause severe disease (e.g. S. epidermidis and subacute endocarditis).
S. aureus is a common cause of boils, sties and skin infections. Serious (life-threatening) infections (pneumonia, deep abscesses, meningitis) may occur in debilitated persons. Slide 7: S. aureus is the most common cause of Gram-positive bacteremia, most commonly involving hospital strains of the organism.
S. aureus is also responsible for scalded skin syndrome and toxic shock syndrome. It is the most common cause of food poisoning. Symptoms occur only a few hours following ingestion of preformed enterotoxin but large amounts of toxin are required s. aureus (disease resulting from direct organ invasion by the bacteria) : s. aureus (disease resulting from direct organ invasion by the bacteria) Pneumonia
Acute bacterial endocarditis
UTI (urinary tract infection) Staphylococcal septicemia : Staphylococcal septicemia Resected femur in a patient with draining osteomyelitis : Resected femur in a patient with draining osteomyelitis Slide 11: DIAGNOSIS:
Clinical: Generally, a Gram stain of exudate from a lesion can demonstrate the characteristic Gram-positive cocci arranged in clusters.
Laboratory: Isolation techniques employ blood agar, mannitol salt agar or potassium-tellurite agar. Bacteriophage testing or serotyping may be utilized Differential diagnosis : Differential diagnosis Other entities causing rash, hypotension, or fever that may be confused with staphylococcal TSS include:
the septic shock syndrome
Rocky Mountain spotted fever
viral infection with exanthem (such as measles or EBV)
Meningococcemia by N.meningitidis
drug-induced reactions (such as erythema multiforme or toxic epidermal necrolysis)
A thorough history with particular attention to tick exposures, ill contacts, travel, pets, and medication use is essential in excluding the mimicking conditions. How to differentiate staph from sterp : How to differentiate staph from sterp You can do 3 things:
Catalase test: all Staphylococcus have the enzyme catalase
Culture: Staphylococcus aureus and certain streptococci are beta-hemolytic (completely hemolyze red blood cells on an agar plate) Slide 14: CONTROL:
Sanitary: There is virtually no possibility to eliminate these organisms because they are (and have been) a significant part of human normal flora. To control the spread of disease, however, clean hospitals and proper food handling are paramount.
Immunological: Nothing really available. But, a new vaccine is in clinical trials
Chemotherapeutic: Antibiotics can be used if life-threatening. One should use penicillin if the particular strain is susceptible. Otherwise, methicillin, oxacillin, cephalosporins or vancomycin may be required. Often, surgical drainage is an important treatment.