2. Staphylococcus
Skin infection, osteomyelitis, food poisoning, foreign body infections, MRSA (Methicillin-resistant Staphylococcus aureus)

3. 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

4. S. aureus morphology

5. Staphylococcus aureus
Food Poisoning

6. 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

7. 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 inanimate objects

8. 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

9. Blood agar plate, S. aureus

10. How did the chef get a staph infection?
Staph is found on any inanimate surface
Staph is often found associated with the external nasal passages 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 to hand contact
Staph can penetrate the deep tissues of skin damaged by
burns
cuts
insect bites
skin diseases—acne, eczema

11. 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 the release of live bacteria and associated toxin
boils
carbuncle

12. 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

13. Abscess and boil formation (cont’d)
St. aureus produces coagulase which converts soluble fibrinogen in plasma to insoluble matrix fibrin
There are two types of coagulase
bound coagulase on the surface of the bacteria causes the bacteria to clump together
free coagulasesecreted from the bacteria into the environment

14. Why produce coagulase
Bound coagulase causes bacteria to clump together. Why?
the more bacteria in a given location the more effective they are in
shielding each other from an immune response and in
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

15. Pus formation is due to an immune response inside the fibrin clot
Many bacteria are found in fibrin clot
Also some immune cells did get trapped in fibrin clot
Immune cells want to kill St. aureus
St. aureus wants to kill immune cells
The war that ensues leads to pus formation
Pus consists of dead and living St. aureus, dead neutophils and plasma inside a fibrin clot

16. Pus formation continued
The immune cells killing St. aureus
neutrophils surround bacteria, ingest them and produce lysosomal enzymes that kill bacteria.
This releases bacterial components that lead to a greater inflammatory response which kills host cells.
St. aureus killing immune cells
when 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

17. 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

18. Staph enterotoxin causes gastro-enteritis in two ways
VOMITINGtoxin works on the vomiting control center of the brain this leads to reversal of peristalsis and vomiting
DIARRHEAenterotoxin is a superantigen and elicits a strong immune response in the region where the toxin is most concentrated. Immune response causes a loss of brush borders in intestinal epithelial cells; these cells cannot absorb water from the gut.

19. Virulence factors of S. aureus
Enzymes:
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

20. 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

22. 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

23. 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

24. Cutaneous lesions of S. aureus

25. Staphylococcal Disease
Systemic infections
Osteomyelitis – infection is established in the metaphysis; abscess forms
Bacteremia – primary origin is bacteria from another infected site or medical devices; endocarditis possible

26. Staphylococcal osteomyelitis in a long bone

27. 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

28. Effects of staphylococcal toxins on skin

29. Toxic Shock Syndrome Toxin
Superantigen
Non-specific binding of toxin to receptors triggers excessive immune response

30. TSS Symptoms 8-12 h post infection Fever Susceptibility to Endotoxins
Hypotension
Diarrhea
Multiple Organ System Failure
Erythroderma (rash)

31. 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, a corticosteriod inhibitor of TNF-a synthesis

32. Coagulase-negative Staphylococci
Coagulase-negative staphylococcus; frequently involved in 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

33. Identification of Staphylococcus in Samples
Frequently isolated from pus, tissue exudates, sputum, urine, and blood
Cultivation, catalase, biochemical testing, coagulase

34. Catalase test

36. Clinical Concerns and Treatment
95% have penicillinase and are resistant to penicillin 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

38. Prevention of Staphylococcal Infections
Universal precautions by healthcare providers to prevent nosocomial infections
Hygiene and cleansing