Staphylococcus

Topic 1

morphological characteristics of staphylococcus

• perfectly spherical gram-positive cocci

• 0.5 to 1 u in diameter

• grows in clusters like a bunch of grapes

greek term

staphylo

2 pigmented colony types

S. aureus and S. epidermidis/ S. albus

S. aureus colony type

golden yellow

S. epidermis/S. albus colony type

white

habitat of S. aureus

nasal passages, skin, oral cavity, and intestinal tract

habitat of S. epidermidis

inhabitant of the skin

surface proteins

• promotes colonization of host tissues such as those that promote attachment to the host

• Infections associated with in-dwelling devices such as IV catheters, prosthetic joints, replacement heart valves, etc.

laminin and fibronectin

• surface proteins that promote attachment to host proteins

• forms part of the extracellular matrix

fibronectin

• present on epithelial and endothelial surfaces as well as a component of blood clots

• has fibrinogen/fibrin binding (clumping factor) which promotes attachment to blood clots and traumatized tissues

• collagen-binding factor

Infections associated with in-dwelling devices such as IV catheters, prosthetic joints, replacement heart valves, etc.

• biometrical implanted in the human body in the human body becomes coated with complex mixture of host proteins and platelets

• fibrinogen is a dominant component —> adherence to S. aureus

• Fibronectin becomes predominant ligand promoting attachment

what happens when IV, catheters, etc. are left in the body for long periods

fibrinogen is degraded and no longer promotes bacterial attachment

factors that inhibit phagocytosis

• capsules, immunoglobulin-binding protein A

capsular polysaccharide

surface polysaccharide of serotype 5 or 8

capsule

• colorless structure

• it does not absorb color or stain

• can interfere with phagocytosis

  • function not clear but may impede phagocytosis

• polysaccharide is rapidly lost upon laboratory subculture

protein A surface protein of S. aureus

• binds with lgG the wrong way by non-immune mechanisms and disrupts opsonization and phagocytosis

• fixes complement

leukocidin

a toxin that specifically acts on polymorphonuclear leukocytes

• toxins that specifically kill white blood cells or polymorphonuclear cells (PMN)

protein toxins

• responsible for symptoms during infection

• membrane damaging toxins

alpha protein

• Best characterized and most potent membrane-damaging toxin; major virulence factor

• Binds to membrane of susceptible cells, its subunits oligomerize to form hexameric rings, a central pore through which cellular contents leak

  • Produces hexameric ring which disintegrates the wall and kills the cell of the host once it has damage 

• Human platelets and monocytes have high affinity to toxin

• A complex series of secondary reactions that cause release of eicosanoids and cytokinesis (dilate of blood vessels, leak of fluids = causes hypovolemia which then septic shock) which trigger the production of inflammatory mediators that produce the symptoms of septic shock

beta toxin

• Sphingomyelinase C damages membranes that is rich in lipids

• Classical test is the lysis of sheep RBC, at 4C to 15C produces incomplete hot-cold lysis

• Produced alpha hemolysis

delta toxin

• Small peptide toxin produced by most strains of S. aureus

• A phospholipase which role in disease is not known

• Incomplete = green; complete = transparent (for hemolysis)

gamma toxin and leucocidin

• Two-component toxin that damages membrane of susceptible cells 

• Produce separately but act together to damage membranes

• Expresses 3 proteins

  • B and C forms leukotoxin with poor hemolytic activity

    • Destroy WBR but seldom kills RBC

  • A and B are hemolytic and weakly leukotoxic

    • Destroy RBC but seldom kills WBC

• Panton and valentine (PV) leucocidin distinct from leukotoxin by gamma hemolysin; has potent leukotoxicity but non-hemolytic

  • OV leucocidin is an important factor in necrotizing skin lesions such as dermonecrosis when injected SC in rabbits

superantigens

enterotoxins and toxic shock syndrome toxin (TSST1)

enterotoxins

• has 6 serotypes: A, B, C, D, E, and G

• causes diarrhea and vomiting (staphylococcus food poisoning)

• toxic shock syndrome = causes fluid to leave —> hypobulimic shock

TSST1

• weakly related to enterotoxin and does not have emetic activity

• responsible for 75% of TSS including menstrual cases: tampon-related TSS not a true infection

• superantigens stimulate T-cells without normal antigenic recognition, result to the release of cytokines in large amounts causing symptoms of TSS

epidermolytic

• exfoliative toxin = ET

• causes scalded skin syndrome in neonates with widespread blistering and loss of epidermis

• 2 forms:

  • ETA

  • ETB

• proteases activity

• possibly the toxin targets a specific protein involved in maintaining the integrity of epidermis

cellular proteins

• coagulase

• staphylokinase

• enzymes

• hyaluronidase

• epidermidis

coagulase

• plasma or blood specific

• binds with prothrombin in the host to form staphylothrombin

• traditional marker for identifying S. aureus

staphylothrombin

causes the activation of proteases activity of thrombin, resulting to conversion of fibrinogen to fibrin and the formation of clots in plasma

coagulase and clumping factors are separate entities

• Coagulase extracellular protein through small fraction is tightly bound on bacterial cell surface and reacts with prothrombin 

• Clumping factor is fibrinogen-binding determinant on S. aureus cell surface, sometimes referred to as bound coagulase

staphylokinase

• Kinase = dissolves/breaks 

• Plasminogen activator

• Complex formed between staphylokinase and plasminogen

• Activates plasmin-like proteolytic activity which dissolves fibrin clot

enzymes

• proteases , lipases, deoxyribonuclease (Dnase), and fatty acid modifying enzyme (FAME) 

  • FAME is important in abscesses where it could modify antibacterial lipids and prolong bacterial survival

  • First three provide nutrients for bacteria

hyaluronidase

• Hydrolyzes hyaluronic acid (cementing substance) 

• Spreading factor 

• Breaks hyaluronic acid → causes holes → organisms can enter

• Hyaluronic acid = cementing substance

epidermidis

• Most important coagulase-negative staphylococci (CNS) which is a common commensal of the skin

• Major cause of infections associated with prosthetic devices and catheters 

• Production of characteristic slime = biofilm

cultural and biochemical characteristics of staphylococcus

• S. aureus coagulase and catalase (+), S. epidermidis coagulase (-) but catalase (+)

• Salt tolerant, S. aureus ferments mannitol, S. epidermidis does not

epidemiology of staphylococcus

epidemiological tracing traditional phage typing but has limitations

disease - S. aureus

• botryomycosis in horses

• mastitis

• tick pyemia in lambs

• facial periorbital eczema in sheep

• purulent synovitis in poultry

• cutaneous staphylococcus

• porcine necrotizing staphylococcal endometritis

botryomycosis in horses

stump of spermatic cord after castration site becomes infected, enlarged and sclerotic with pockets of pus containing granules similar to actinomycosis

mastitis

suppurative lesions in cattle, organisms colonize tips of teats

tick pyemia in lambs

• acute septicemia or bacteremia along with toxemia that kills lambs

• ixodes ricinus

purulent synovitis in poultry

bumble foot in turkey

cutaneous staphylococcus

exudative dermatitis in rabbits and subcutaneous

disease - S. epidermidis

opportunistic invader

disease - S. intermedius

most prevalent in drugs and carnivores

disease - S. hyicus subsp. Hyicus

• exudative epidermitis of swine

• through breaks on the skin

• moist, greasy exudate on entire body of an animal

• biotin requirement

diagnosis of staphylococcus

• Smears

• Culture on BAP

• Mannitol salt agar (MSA) 

• Coagulase

• Deoxyribonuclease

immunity

no effective vaccine

antimicrobial resistance

• beta lactamase

• methicillin resistant S. aureus (MRSA) or multiple-drug resistant