• staphylococcus: catalase positive
• streptococcus/enterococcus: catalase negative

what bacterial species uniquely expresses coagulase?

S. aureus

This is the only staph species that expressed coagulase, and so its presence can be used to diagnose or to exclude S.aureus.

Coagulase is an enzyme that converts fibrinogen into fibrin and is located on the surface of S.aureus. It converts fibrinogen upon exposure to blood, creating a coating on the bacterial surface. This coating makes phagocytosis less effective.

what are some clinically noteworthy coagulase-negative staphylococci?

• S.epidermidis: most common isolate
• S.lugdunenis: endocarditis
• S. saprophyticus: UTI

staphylococci can grow in diverse environments. what are some of the characteristics that enable this?

• facultative anaerobes
• can grow in high salt concentrations (around 10%NaCl)
• can grow in wide range of temperatures

• stable gram positive peptidoglycan layer enables survival on dry surfaces for prolonged periods of time
• capsule: polysaccharide outer layer that covers bacterial cell well; inhibits chemotaxis and phagocytosis
• slime layer: loose surface film made of monosacchs, proteins, and small peptides; inhibits chemotaxis and phagocytosis; aids in adhesion to cell surfaces and implants, etc
• protein A: surface protein that binds IgG Fc fragments, coating bacteria with IgG and interfering with phagocytosis by blocking interaction between Fc receptors on neutrophils and IgG

what role do surface adhesion proteins play in staphylococcus pathogenicity?

numerous staph proteins (like protein A) bind to host proteins (ie: fibrinogen, fibronectin, elastin, collagen) and facilitate adherence to host tissues

adherence is first step towards colonization...leading to infection

enzymes are an important virulence factor of Staph. Name and describe critical enzymes employed by Staph.

• coagulase: used by S. aureus ONLY. converts fibrinogen to fibrin (clot formation).
• catalase: catalyzes conversion of toxic H202 (produced by phagocytic cells) into H20
• hyaluronidase: hydrolyzes hyaluronic acid present in connective tissues, thus promoting spread of staph in tissue
• fibrinolysin, lipases, nucleases: dissolves fibrin clots, lipids, and DNA
• penicillinase (ß-lactamase): hydrolyzes penicillins
• lipases
• nucleases

what virulence factor is responsible for the tissue destruction characteristic of staph infections?

cytotoxins!

• toxic for most WB/RBCs, platelets, fibroblasts
• dissolve cell membranes or insert pores
• Panton-Valentine (PV cytotoxin) is characteristic of extremely virulent community-acquired S.aureus

the cytolytic peptides (produced by all S.aureus isolates) are OVERPRODUCED by S. aureus strains responsible for MRSA

responsible for recruiting and then lysing neutrophils 

what causes staphylococcus scalded skin syndrome (SSSS) aka RITTER's DISEASE aka PEMPHIGUS NEONATORUM?

serine proteases split the intercellular bridges in the stratum granulosum epidermis

responsible for the pediatric disease staphylococcus scalded skin syndrome

• heat stable (100 centigrade for 30 minutes)
• resistant to gastric acids and digestive enzymes
• superantigens that stimulate T cells and release of cytokines(kick immune response into overdrive...)
• stimulates inflammatory mediators from mast cells to be released, leading to increased intestinal peristalsis and fluid loss, nausea, and vomiting
• responsible for clinical manifestations of staph food poisoning

• superantigen that stimulates prolif of T cells and release of cytokines
• produces leakage or cellular destruction of endothelial cells
• responsible for multi-organ failure of Staph Toxic Shock Syndrome

• oxacillin/methicillin: mediated by acquisition of new PBP
• erythromycin and clindamycin: mediated by alteration of ribosome
• vancomycin: mediated by acquisition of vanA genes

what are common diagnostic markers of S.aureus infection?

• coagulase
• protein A (common test when combined with coagulase)

• slime layer! - a monosaccharide layer that enables adhesion to surfaces of cells, stents, sutures, etc
• do not usually express toxins like in S.aureus
• do have many of the enzymes (catalase, hyaluronidase, etc) so that they are able to also cause much tissue destruction in right setting

what are some common cutaneous S.aureus infections?

• impetigo: superficial skin layers; small flattened macule progressing to a puss-filled vesicle (pustule) with erythematous base
• folliculitis: pyogenic infection of hair follicle; if it involves base of eyelide it is a stye
• furuncle (boils): progression of impetigo or folliculitis characterized by large, painful, pus-filled nodules
• carbuncles: furuncles that have coalesced and extended to the subcutaneous tissues

carbuncles: furuncles that have coalesced and extended to the subcutaneous tissues

what are the commonest toxin mediated S.aureus diseases?

• Toxic Shock Syndrome
• S.aureus mediated food poisoning
• Scalded skin syndrome

what is typically present in S.aureus wound infections?

staph infections that develop after trauma or surgical event

typically a foreign body (ie: splinter, suture) is present

• accumulation of dead host cells creates the pus found in pyogenic infections

what are some examples of purulent, pyogenic S.aureus infections?

• pneumonia and empyema
• osteomyelitis
• septic arthritis
• endocarditis

• pus collection in the lungs and pleural space around the lungs; newly recognized, severe form of CA-necrotizing pneumonia caused by MRSA
• An empyema is a collection of pus within a naturally existing anatomical cavity, such as the lung pleura. It must be differentiated from an abscess, which is a collection of pus in a newly formed cavity.

purulent infection in bones characterized by bony destruction

purulent infection of the inner lining of the heart, particularly with heart valve involvement

dissemination of S.aureus in blood from a localised infection (ie:cutaneous) or colonized location (ie:mouth) to a generally sterile site

• localized infection with SYSTEMIC SPREAD of the TOXIN (not organism) to the superficial layers of skin
• clinical symptoms caused by toxin produced by the bacteria and NOT by the spread of the bacteria itself
• exfoliative toxin A or B
• common in peds
• abrupt onset of redness and inflammation around the mouth (perioral erythema) progresses to cover entire body
• cutaneous blisters progress to desquamation
• Abs lead to recovery; no scarring
• duration 7-10days, low mortality

• foods: salty processed (ie:ham), custards, ice cream, potato salad
• intoxication
  • produced by toxin present in the food
• develops w/in 4 hous of consumption:
  • acute vomiting, watery & nonbloody diarrhea, abdominal pain
  • no fever
  • short incubation and duration (median duration ~24hrs)
• one of 8 serologically distinct strains are responsible for disease: enterotoxin A is most common
  • toxins are heat stable and resistant to hydrolysis by gastric acid and digestive enzymes
  • so: can be present in heated foods and survive passage through stomach

disease onset is abrupt with fever, hypotension, and diffuse erythematous rash

multiorgan involvement (GI, musculoskeletal, renal, etc)

skin will desquamate (peel) eso on palms and soles

toxin spreads systematically despite the fact that the organisms remain localised to the mucosal surface or wound where infection is initiated; organism is generally NOT present in blood or involved tissue

what bugs are typically responsible for foreign body infections?

coagulase-negative Staph

• infections originate from skin, transient bacteremia, or introduced at time of surgery (when catheter or shunt placed)
• staph produces slime layer that permits adhesion to foreign body and so can resist phagocytosis or antibiotic therapy
• blood cultures persistently positive bc infected foreign body is in contact with blood typically

do prosthetic joint infections typically have positive blood culture?

• commonly involves prosthetic valves
• contam during surgery
• chronic
• blood cultures + (intravascular infection)
• S. lugdunensis
• difficult to treat

• S. saprophyticus