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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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%

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???

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

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

What is the likely causative organism?

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

What is the treatment?

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

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.

What is the causative organism?

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

What is the treatment?

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

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

Erysipelas

What is the most common causative organsism?

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)

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

Orbital cellulitis – refer urgently

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