Bacterial Skin
Infections
Professor Sudheer Kher
Learning Objectives
Enumerate the microbes causing skin
infections.
Describe the






characteristic clinical manifestations
methods of laboratory diagnosis
principles of management
methods of prevention of each of the
infections listed.
Bacterial
Infection of Skin
The Skin
Definition
Skin is largest organ of body. Maintains
homeostasis, protects underlying tissues and
organs, protects body from mechanical injury,
damaging substances, and ultraviolet rays of
sun.
Recurrent skin
infections

Recurrent skin infections should raise
suspicion of colonization





Staphylococcal nasal carriage
Resistant strains of bacteria (eg, methicillinresistant Staphylococcus aureus [MRSA]),
Cancer
Poorly controlled diabetes
Other reasons for immunocompromise (eg, HIV,
hepatitis, advanced age, congenital susceptibility).
Pyoderma

Pyoderma is a group name for pyococcal dermatoses
which are generally purulent. In tropical countries,
pyoderma is a common problem, particularly in the
summer and the monsoon.

The two important pyogenic organisms are the
Staphylococcus aureus and the Streptococcus pyogenes.

Follicular infections are mainly due to staphylococci;
while erysipelas and cellulitis are caused by streptococci.

Besides these, other organisms which occasionally come
across in pyodermas are Proteus, Pseudomonas and
Coliform bacilli.
Skin Infections
Infection
Site
Causal Organism
Boil
Hair follicle
Staphylococcus aureus
Carbuncle
Multiple Hair follicles
Staphylococcus aureus
Stye
Hair follicle of eye lash
Staphylococcus aureus
Sycosis barbae
Shaving area
Staphylococcus aureus
Pemphigus neonatorum
Infant’s skin
Staphylococcus aureus
Toxic epidermal
necrolysis
Infant’s skin
Staphylococcus aureus
Pemphigus neonatorum
Infant’s skin
Staphylococcus aureus
Toxic epidermal
necrolysis
Infant’s skin
Staphylococcus aureus
Erysipelas
Face, sometimes limbs
Streptococcus pyogenes
Acne vulgaris
Face & Back
Propionibacterium acnes
S. aureus produces
skin infection
I. Direct infection of skin and adjacent tissues
a.
b.
c.
d.
e.
f.
Impetigo
Ecthyma
Folliculitis
Furunculosis
Carbuncle
Sycosis barbae
II. Cutaneous disease due to effect of bacterial
toxin
a.
b.
Staphylococcal scalded skin syndrome
Toxic shock syndrome
ß-hemolytic
streptococcus produces
skin infection
I. Direct infection of skin or subcutaneous
a.
b.
c.
d.
e.
Impetigo (non bullous)
Ecthyma
Erysipelas
Cellulitis
Necrotizing fascitis
II. Secondary infection
Eczema infection
Folliculitis
Folliculitis is a bacterial infection of hair
follicles.
 Folliculitis is usually caused by
Staphylococcus aureus but occasionally
Pseudomonas aeruginosa (hot-tub
folliculitis) or other organisms. Hot-tub
folliculitis occurs because of inadequate
treatment of water with chlorine or
bromine.

Folliculitis manifests as superficial pustules or
inflammatory nodules surrounding hair follicles.
Furuncles and
Carbuncles
 Furuncles
are skin abscesses caused
by staphylococcal infection, which
involve a hair follicle and surrounding
tissue.
 Carbuncles are clusters of furuncles
connected subcutaneously, causing
deeper suppuration and scarring. They
are smaller and more superficial than
subcutaneous abscesses
Furuncles (boils) are tender nodules or pustules caused
by staphylococcal infection. Carbuncles are clusters of
furuncles that are subcutaneously connected.
Carbuncles
Treatment of
folliculitis

Because most folliculitis is caused by S. aureus, clindamycin 1%
lotion or gel may be applied topically bid for 7 to 10 days.
Alternatively, benzoyl peroxide 5% wash may be used when
showering for 5 to 7 days. Extensive cutaneous involvement may
warrant systemic therapy (eg, cephalexin 250 to 500 mg po tid to
qid for 10 days).

If these measures do not result in a cure, or folliculitis recurs,
pustules are Gram stained and cultured to rule out gram-negative or
methicillin-resistant S. aureus (MRSA) etiology, and nares are
cultured to rule out nasal staphylococcal carriage. Potassium
hydroxide wet mount should be done on a plucked hair to rule out
fungal folliculitis.

Treatment for MRSA usually requires two oral antibiotics, and the
choice of therapeutic drugs should be based on culture and
sensitivity reports.

Hot-tub folliculitis usually resolves without treatment. However,
adequate chlorination of the hot tub is necessary to prevent
recurrences and to protect others from infection.
Hidradenitis suppurativa
 Hidradenitis
suppurativa is a chronic,
scarring inflammation of apocrine glands
of the axillae, groin, and around the
nipples and anus.
Cellulitis
 Cellulitis
is acute bacterial infection of
the skin and subcutaneous tissue most
often caused by streptococci or
staphylococci.
Treatment of
cellulitis

Treatment is with antibiotics. For most patients, empiric
treatment effective against both group A streptococci and S.
aureus is used.

Oral therapy is usually adequate with dicloxacillin 250 mg or
cephalexin 500 mg po qid for mild infections. Levofloxacin 500
mg po once/day or moxifloxacin
400 mg po once/day works well for patients who are unlikely to
adhere to multiple daily dosing schedules.

For more serious infections, oxacillin or nafcillin 1 g is given IV
q 6 h.

Immobilization and elevation of the affected area help reduce
edema; cool, wet dressings relieve local discomfort.
Cutaneous Abscess
A
cutaneous abscess is a localized
collection of pus in the skin and may
occur on any skin surface.
Erysipelas





Erysipelas is a type of superficial cellulitis with dermal
lymphatic involvement.
Erysipelas is characterized clinically by shiny, raised,
indurated, and tender plaque-like lesions with distinct
margins.
Erysipelas is most often caused by group A (or rarely
group C or G) β-hemolytic streptococci and occurs
most frequently on the legs and face.
Other causes - Staphylococcus aureus (including
methicillin-resistant S. aureus [MRSA]), Klebsiella
pneumoniae, Haemophilus influenzae, Escherichia
coli.
It is commonly accompanied by high fever, chills, and
malaise. Erysipelas may be recurrent and may result
in chronic lymphedema.
Erysipelas is characterized by shiny, raised, indurated,
and tender plaque-like lesions with distinct margins. It is
most often caused by β-hemolytic streptococci and
occurs most frequently on the legs and face.
Erythrasma
 Erythrasma
is an intertriginous
infection with Corynebacterium
minutissimum.
 Most common among patients with
diabetes and among people living in
the tropics.
Impetigo and
Ecthyma
 Impetigo
is a superficial skin infection
with crusting or bullae caused by
streptococci, staphylococci, or both.
 Ecthyma is an ulcerative form of
impetigo.
Impetigo (Non-Bullous)
Non-bullous impetigo is a
superficial skin infection that
manifests as clusters of
vesicles or pustules that
rupture and develop a honeycolored crust.
Impetigo (Bullous)
Bullous impetigo is a superficial
skin infection that manifests as
clusters of vesicles or pustules that
enlarge rapidly to form bullae. The
bullae burst and expose larger
bases, which become covered with
honey-colored varnish or crust.
Ecthyma is a skin infection
similar to impetigo, but more
deeply invasive. Usually caused
by a streptococcus infection,
ecthyma goes through the outer
layer (epidermis) to the deeper
layer (dermis) of skin, possibly
causing scars.
Ecthyma gangrenosum is a
bacterial skin infection (caused
by Pseudomonas aeruginosa)
that usually occurs in people
with a compromised immune
system.
Necrotizing Subcutaneous Infection
(Necrotizing Fasciitis)

Typically caused by a mixture of aerobic and anaerobic
organisms that cause necrosis of subcutaneous tissue, usually
including the fascia.

This infection most commonly affects the extremities and
perineum. Affected tissues become red, hot, and swollen,
resembling severe cellulitis.

Without timely treatment, the area becomes gangrenous. Patients
are acutely ill. Diagnosis is by history and examination and is
supported by evidence of overwhelming infection.

Treatment involves antibiotics and surgical debridement.
Prognosis is poor without early, aggressive treatment.
Necrotising fasciitis
Treatment
1.Surgical
debridement
2.Antibiotics
3.Amputation if necessary
Bacterial Infection
of Skin
Lab. Diagnosis
Specimen collection.
1. Skin biopsy
2. Skin swab
3. Pus swab
4. Nasal / skin swab
Lab. Diagnosis
Suspected organisms
 Impetigo:
Group A Streptococcus, Staphylococcus
aureus
 Folliculitis: Staphylococcus aureus, Pseudomonas
aeruginosa
 Furuncles: Staphylococcus aureus
 Carbuncles: Staphylococcus aureus
 Cellulitis:
Group A Streptococcus, Staphylococcus
aureus, Hemophilus influenzae
 Erysipelas: Group A Streptococcus
 Necrotizing fasciitis: Group A Streptococcus,
Clostridium perfringens and
other species, Bacteroides fragilis,
the anaerobes, Enterobacteriaceae,
Pseudomonas aeruginosa
Principles of therapy of
pyoderma
Good personal hygiene
 Management of predisposing factors
 Local

Attend to traumas, Pressure, Sweating, Bites
 Treat pre-existing dermatosis
 Investigate carrier sites: Nose, Axilla, Perineum

Systemic
Treatment of disease like DM
 Nutritional deficiency
 Immunodeficiency

Principles of therapy of
pyoderma
 Local

therapy
Cleaning with soap-water and weak
KMN04 solution

Removal of crusts with KMN04 solution

Application of antibacterial cream
 Systemic

therapy
Antibiotics
Recurrent staphylococcal
infection

Persistent nasal carriage

Abnormal neutrophilic chemotaxis

Deficient intracellular killing

Immunodeficient status

D.M.
Staph. carriage elimination

Nasal & perineal care

Rifampicin 600 mg/d 7-10 days

Clindamycin 150 mg/d 3 months

Topical mupirocin

Replacement of microflora with a less
pathogenic stains of S.aurus (strain 502)
Antibiotic Resistance Profiles
of MRSA








100% B-lactam antibiotics
94% resistant to clindamycin and erythromycin
89% resistant to ciprofloxacin
56% resistant to trimethoprimsulfamethoxazole
33% resistant to tetracycline
3% resistant to rifampin
3% resistant to fusidic acid
2% resistant to mupirocin