1. Bacterial Skin Infections Dr. Hani MasaadehMD, PhD Lecture objectives
Normal Skin Flora \

2. Natural Defenses of the Skin
Keratin
Skin sloughing
Sebum: low pH, high lipid
Sweat: low pH, high salt, and
Lysozyme, which digests peptidoglycan

3. Normal Flora of the Skin
Large numbers of microorganisms live on or in the skin
Numbers of bacteria are determined by location and moisture content
Skin flora are opportunistic pathogens
Most skin flora can be categorized in three groups:
diphtheroids
staphylococci
yeasts

4. Normal Skin Flora Propionibacterium acnes Corynebacterium sp.
Staphylococci
Staphylococcus epidermidis
Staphylococcus aureus
Streptococci sp.
Candida albicans (yeast)
Many others

5. Normal Flora of the Skin
Diphtheroids
Named for their resemblance to Corynebacterium diphtheriae
Toxin inhibits elongation factor 2
Gram-positive bacteria with varied shape and low virulence
Non-toxin producers like C. diphtheriae
Responsible for body odor
Odor caused by the bacterial break-down of sweat
Common diphtheroid is Propionibacterium acnes

6. Normal Flora of the Skin
Staphylococci
Gram-positive, salt-tolerant organism
Relatively avirulent
Can cause serious disease in immunocompromised people
Principal species is Staphylococcus epidermidis
Functions on the skin to prevent colonization of pathogenic flora
Maintains balance among microbial skin flora

7. Normal Flora of the Skin
Fungi (yeast)
Tiny lipophilic yeast universally found on normal skin
Usually from late childhood throughout life
Fungi shapes vary among strains
Usually round or oval; however, can be short rods
Fungi found on skin are generally harmless
Can cause skin conditions such as rash or dandruff

8. Acne Microscopy Propionibacterium acnes: Gram + rod Digests sebum
Attracts neutrophils
Neutrophil digestive enzymes cause lesions, “pus pockets”
Microscopy

9. Acne
Most common skin
disease in humans
Oil-based cosmetics worsen disease
No effects of diet

10. Acne Treatments
Benzoyl peroxide dries plugged follicles, kills microbes
Tetracycline (antibiotic)
Accutane – inhibits sebum formation

11. Hair Follicle Infections
Symptoms – Folliculitis
Presents as a small red bump or pimple
Infection can spread from infected follicle to adjacent tissues
Causes localized redness, swelling and tenderness
The lesion produced is called a furuncle
Most are caused by Staph aureus

12. Scalded Skin Syndrome Staphylococcal scalded skin syndrome (SSSS)
Toxin-mediated disease
Occurs primarily in infants
Potentially fatal

13. Scalded Skin Syndrome Symptoms Skin appears to be burned (scalded)
Begins as generalized redness
Other symptoms include malaise, irritability, fever
Nose, mouth and genitalia may be painful before other indicators become apparent
Within 48 hours of infection, symptoms manifest
Skin becomes red and wrinkled
Large fluid-filled blisters appear
Skin is tender to the touch and may feel like sandpaper

14. Scalded Skin Syndrome Causative Agent
Bacterial agent is Staphylococcus aureus
Disease is due to the production of toxins produced by S. aureus
Toxins are call exfoliatins
Exfoliatins destroy integral layers of the outer epidermis
Toxins are coded either by plasmid or on the bacterial chromosome

15. Scalded Skin Syndrome Epidemiology
5% of S. aureus strains produce exfoliatins
Disease can appear in any age group
Most frequently seen in infants, the elderly and immunocompromised
Transmission is generally person-to-person
Disease is usually isolated; however, small epidemics can occur in nurseries

16. Scalded Skin Syndrome Prevention and Treatment
Only preventative measure is patient isolation
Patients are in protective isolation
Helps limit spread of bacterial agent
Limits patient exposure to potential secondary pathogens
Treatment includes bactericidal antibiotics
Antistaphylococcals such as penicillinase-resistant penicillin
Treatment also includes removal of dead skin to prevent secondary infection

17. Streptococcal Impetigo
Pyoderma infection
Characterized by pus production
Pyodermas can result from insect bites, burns and scrapes
Such injuries can be so slight that they miss detection
Impetigo is most common type of pyoderma

18. Streptococcal Impetigo
Causative Agent
Many cases including epidemics are caused by Streptococcus pyogenes
S. aureus is also implicated as a causative agent
S. pyogenes is a Gram-positive, β hemolytic cocci
Often referred to as Group A
Due to presence of group A cell wall polysaccharide
Streptococcus species also form the characteristic chain formation

19. Rocky Mountain Spotted Fever
First recognized in Rocky Mountain region of United States
Representative of a group of rickettsial diseases
Transmitted by ticks

20. Rocky Mountain Spotted Fever
Symptoms
Distinguished by initial rash of faint pink spots
Appears first on palms, wrists, ankles and soles of feet
Rash eventually spreads to other parts of the body
Spots become raised bumps and are hemorrhagic
Shock or death can occur when certain body systems become involved
Especially the heart and kidney

21. Rocky Mountain Spotted Fever
Causative Agent
Rickettsia rickettsii
Obligate, intracellular bacterium
Requires host organism for survival
Gram-negative, non- motile, coccobacillus
Bacteria are very small and often difficult to see in gram stain

22. Rocky Mountain Spotted Fever
Epidemiology
Zoonotic disease
Occurs in areas in the United States, Canada and Mexico
Highest incidence in US is in south Atlantic and south-central United States
Maintained in several species in nature
Primarily in ticks and certain mammals
Main vectors include wood tick, Dermacentor andersoni and the dog tick, Dermacentor variabilis
Tick vectors remain infected for life

23. Rocky Mountain Spotted Fever
Prevention
No vaccine currently available
Prevention should be directed towards:
Avoiding tick-infested areas
Using protective clothing
Using tick repellents containing DEET
Carefully inspect body
Especially dark, moist areas
Remove attached ticks carefully
Avoid crushing and contaminating bite area
Treatment
Antibiotics are highly effective in treatment if given early
Doxycycline and chloramphenicol used most often
Without treatment, overall mortality reaches approximately 20%
With early diagnosis and treatment, mortality rates drop to less than 5%

24. Why does skin get infected?
There are multiple types of bacteria which are normally present on the skin.
For example: Staphylococcus epidermidis and yeasts
The presence of bacteria does not automatically lead to a skin infection
What is the difference between colonisation and infections???

25. Colonisation: Bacteria are present, but causing no harm
Infection: Bacteria are present and causing harm.
A break in the epidermal integrity can allow organisms to enter and become pathogenic. This can occur as a result of trauma, ulceration, fungal infection, skin disease such as eczema
The stratum corneum of the epidermis is important in maintaining a barrier against skin infections

26. Impetigo
A highly infectious skin disease, which commonly occurs in children.

27. What is the likely causative organism?

28. The causative organism is usually Staphylococcus Aureus (>90% cases1), but less often can be strep pyogenes.
Begins as a vesicle, which may enlarge into a bulla.
Weeping, exudative area with characteristic honey coloured or golden, gummy crusts, which leave denuded red areas when removed.
May present as macules, vesicles, bullae or pustules
Bullae are more prominent in staphylococcal infection and in infants

29. What is the treatment?

30. Impetigo
Treatment:
Mild localised cases - use topical antibiotic Polyfax
Widespread or more severe infections – use systemic antibiotics, such as flucloxacillin (or erythromycin if penicillin allergic)
Up to 10 days if needed. NB if the primary skin problem is not treated, the infection may not settle eg underlying eczema needs treating as well

31. Folliculitis Inflammation of the hair follicle.
Presents as itchy or tender papules and pustules at the follicular openings.
Complications include abscess formation and cavernous sinus thrombosis if upper lip, nose or eye affected.
Sycosis Barbae is a variant which occurs in the beard area, ofen spread by shaving. Pseudofollicultis is not an infection, but an inflammatory condition caused by ingrowing hairs.

32. What is the causative organism?

33. Most common cause is Staph Aureus.
Other organisms to consider include:
Gram negative bacteria – usually in patients with acne who are on broad spec antibiotics
Pseudomonas (“Hot tub folliculitis”)
Yeasts (candida and pityrosporum)
Hot tub – typically occurs 1-4 days after bathing in unchlorinated contaminated water

34. What is the treatment?

35. Folliculitis treatment
Topical antiseptics such as Chlorhexidine
Topical antibiotics, such as Fusidic acid or Mupirocin
More resistant cases may need oral antibioics such as Flucloxacillin
Hot tub folliculitis – ciprofloxacin2
Gram negative – trimethoprim

36. Cellulitis Infection of the deep subcutaneous layer of the skin
Presents as a hot, tender area of confluent erythema of the skin
Can cause systemic infection with fever, headache and vomiting.
Erysipelas is more superficial and has a more well demarcated border
Treatement same and can coexist

37. Erysipelas

38. What is the most common causative organsism?

39. Cellulitis Streptococcus – Group A Strep Pyogenes.
Others include Group B, C, D strep, Staphylococcus Aureus, haemophilus influenzae (children) and anaerobic bacteria (e.g Pasteurella spp. After animal bites)

40. Treatment of cellulitis
Oral Flucloxacillin or erythromycin if allergic
Co-amoxiclav in facial cellulitis
If severe systemic upset, may require admission for IV antibiotics.
After the acute attack has settled, especially in recurrent episodes – consider the underlying cause

41. Orbital cellulitis – refer urgently

42. Furunculosis (boils) and carbuncles
Deeper Staphylococcal abscess of the hair follicle
Coalescence of boils leads to the formation of a carbuncle
Treatment is with systemic antibiotics and may need incision and drainage.
Consider looking for underlying causes, such as diabetes