2266 staph
TRANSCRIPT
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 1/38
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 2/38
Staphylococcus
Skin infection, osteomyelitis, food poisoning,
foreign body infections, MRSA (Methicillin-
resistant Staphylococcus aureus)
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 3/38
General Characteristics of
the Staphylococci• Common inhabitant of the skin and mucous
membranes
• Spherical cells arranged in irregular clusters
• Gram-positive
• Lack spores and flagella
• May have capsules• 31 species
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 4/38
S. aureus morphology
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 5/38
Staphylococcus aureus
Food Poisoning
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 6/38
St. aureus and food poisoning
• St. aureus causes gastro-enteritis
• Food poisoning is not caused by the organism
but by the toxin that the organism secretes
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 7/38
Properties of St. aureus that make it
persistent in nature
• Relatively heat resistant
• Resistant to high concentrations of salt
• Can survive long periods on dry inanimateobjects
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 8/38
Staphylococcus aureus
• Grows in large, round, opaque colonies
• Optimum temperature of 37oC
• Facultative anaerobe
• Withstands high salt, extremes in pH, and
high temperatures
• Produces many virulence factors
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 9/38
Blood agar plate, S. aureus
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 10/38
How did the chef get a staph infection?
• Staph is found on any inanimate surface
• Staph is often found associated with the external nasalpassages of 30% of the human population
• Staph is often found on skin surfaces because they can tolerate
the low moisture and high salt content of skin• Staph can easily spread from person to person via hand tohand contact
• Staph can penetrate the deep tissues of skin damaged by
burns
cutsinsect bites
skin diseases — acne, eczema
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 11/38
What happens when Staph enters a
wound and how does this relate to food
poisoning ?
• Localized staph infection leading to an
abscess (collection of pus)
boils=abscesses in the skin
carbuncle=interconnected abscesses
• Rupture of the abscess leads to therelease of live bacteria and associated
toxin
boils
carbuncle
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 12/38
How do abscesses and boils form?
• Chef cuts arm and Staph enters deeper skin layer
• St. aureus is surrounded by a capsule thick slime layer
that prevents an immediate immune response
• Bacteria multiply at the site surrounded by the capsule
• St. aureus establishes intimate contact with skin cells
via bacterial techoic acids and fibronectin skin cell
receptors
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 13/38
Abscess and boil formation (cont’d)
• St. aureus produces coagulase which convertssoluble fibrinogen in plasma to insolublematrix fibrin
• There are two types of coagulasebound coagulase on the surface of the
bacteria causes the bacteria to clump together
free coagulasesecreted from thebacteria into the environment
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 14/38
Why produce coagulase
• Bound coagulase causes bacteria to clump together.
Why?
the more bacteria in a given location the more effective they are in
1. shielding each other from an immune response and in
2. excreting toxic factors in high quantities
• Free coagulase causes a protective fibrin clot to form
around bacteria. Why?bacteria can grow and divide in protective environment; most immune
cells have been denied entry to the region
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 15/38
Pus formation is due to an immune
response inside the fibrin clot• Many bacteria are found in fibrin clot
• Also some immune cells did gettrapped in fibrin clot
• Immune cells want to kill St. aureus
• St. aureus wants to kill immune cells
• The war that ensues leads to pusformation
• Pus consists of dead and living St.aureus, dead neutophils and plasmainside a fibrin clot
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 16/38
Pus formation continued
• The immune cells killing St. aureus
neutrophils surround bacteria, ingest them and produce lysosomal enzymes that killbacteria.
This releases bacterial components that lead to a greater inflammatory responsewhich kills host cells.
• St. aureus killing immune cellswhen neutrophils ingest bacteria the lysosome fuses with the phagosome
St. aureus produces catalase that converts hydrogen peroxide into water and oxygen
St. aureus produces cytotoxins that kill the neutorphils
The dead neutrophils release lysosomal campartment enzymes that will may kill St.aureus but will kill adjacent host cells
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 17/38
St. aureus and food
• Staph grows and divides in food and produces
an enterotoxin (A-E, G, H, I and J)
• The Staph doesn’t cause food poisoning, the
enterotoxin does
• Enterotoxin is stable to heating at 100oC for 30
minutes.
• Enterotoxin is resistant to degradation by
stomach gastric acids
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 18/38
Staph enterotoxin causes gastro-
enteritis in two ways
• VOMITINGtoxin works on the vomiting controlcenter of the brain this leads to reversal of peristalsisand vomiting
• DIARRHEAenterotoxin is a superantigen andelicits a strong immune response in the region wherethe toxin is most concentrated. Immune response
causes a loss of brush borders in intestinal epithelialcells; these cells cannot absorb water from the gut.
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 19/38
Virulence factors of S. aureusEnzymes:
• Coagulase – coagulates plasma and blood; produced
by 97% of human isolates; diagnostic
• Hyaluronidase – digests connective tissue
• Staphylokinase – digests blood clots• DNase – digests DNA
• Lipases – digest oils; enhances colonization on skin
• Penicillinase – inactivates penicillin
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 20/38
Virulence factors of S. aureus
Toxins:
• Hemolysins (α, β, γ, δ) – lyse red blood cells
• Leukocidin – lyses neutrophils and macrophages
• Enterotoxin – induce gastrointestinal distress• Exfoliative toxin – separates the epidermis from the dermis
• Toxic shock syndrome toxin (TSST) – induces fever,
vomiting, shock, systemic organ damage
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 21/38
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 22/38
Epidemiology and Pathogenesis
• Present in most environments frequented by humans• Readily isolated from fomites
• Carriage rate for healthy adults is 20-60%
• Carriage is mostly in anterior nares, skin,nasopharynx, intestine
• Predisposition to infection include: poor hygiene and
nutrition, tissue injury, preexisting primary infection,
diabetes, immunodeficiency
• Increase in community acquired methicillin resistance
- MRSA
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 23/38
Staphylococcal Disease
Range from localized to systemic• Localized cutaneous infections – invade skin through
wounds, follicles, or glands
– Folliculitis – superficial inflammation of hair follicle; usually
resolved with no complications but can progress
– Furuncle – boil; inflammation of hair follicle or sebaceous
gland progresses into abscess or pustule
– Carbuncle – larger and deeper lesion created by aggregation
and interconnection of a cluster of furuncles
– Impetigo – bubble-like swellings that can break and peel
away; most common in newborns
Cutaneous lesions of S aureus
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 24/38
Cutaneous lesions of S. aureus
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 25/38
Staphylococcal Disease
• Systemic infections
– Osteomyelitis – infection is established in the
metaphysis; abscess forms
– Bacteremia – primary origin is bacteria fromanother infected site or medical devices;
endocarditis possible
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 26/38
Staphylococcal osteomyelitis in a long bone
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 27/38
Staphylococcal Disease
• Toxigenic disease
– Food intoxication – ingestion of heat stable
enterotoxins; gastrointestinal distress
– Staphylococcal scalded skin syndrome – toxin induces bright red flush, blisters, then
desquamation of the epidermis
– Toxic shock syndrome – toxemia leading to
shock and organ failure
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 28/38
Effects of
staphyloco
ccal toxinson skin
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 29/38
Toxic Shock Syndrome Toxin
• Superantigen
• Non-specificbinding of toxin to
receptors triggers
excessive immuneresponse
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 30/38
TSS Symptoms
• 8-12 h post infection
• Fever
• Susceptibility to Endotoxins• Hypotension
• Diarrhea
• Multiple Organ System Failure• Erythroderma (rash)
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 31/38
TSS Treatment
• Clean any obvious wounds and remove any foreign
bodies
• Prescription of appropriate antibiotics to eliminate
bacteria• Monitor and manage all other symptoms, e.g.
administer IV fluids
• For severe cases, administer methylprednisone, acorticosteriod inhibitor of TNF-a synthesis
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 32/38
32
Coagulase-negative Staphylococci
Coagulase-negative staphylococcus; frequently involvedin nosocomial and opportunistic infections
• S. epidermidis – lives on skin and mucous membranes;
endocarditis, bacteremia, UTI
• S. hominis – lives around apocrine sweat glands
• S. capitis – live on scalp, face, external ear
• All 3 may cause wound infections by penetrating
through broken skin
• S. saprophyticus – infrequently lives on skin, intestine,
vagina; UTI
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 33/38
Identification of Staphylococcus in
Samples
• Frequently isolated from pus, tissue exudates,
sputum, urine, and blood
• Cultivation, catalase, biochemical testing,coagulase
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 34/38
Catalase test
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 35/38
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 36/38
Clinical Concerns and Treatment
• 95% have penicillinase and are resistant topenicillin and ampicillin
• MRSA – methicillin-resistant S. aureus –
carry multiple resistance – Some strains have resistance to all major drug
groups except vancomycin
• Abscesses have to be surgically perforated• Systemic infections require intensive
lengthy therapy
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 37/38
8/2/2019 2266 Staph
http://slidepdf.com/reader/full/2266-staph 38/38
Prevention of Staphylococcal Infections
• Universal precautions by healthcare providers
to prevent nosocomial infections
• Hygiene and cleansing