Staphylococcus

Skin Infections
Introduction
Skin:

 The skin has the largest surface area of all of the body organs and is the
most exposed organ.
 It is very effective in providing protection against the external
environment.
 skin infections are common presentations.

Normal flora of the skin:

 Mainly Gram positive – Staphylococci, Streptococci, Cutibacterium acnes,
etc.
Pathogens
 Bacteria:
 Genus: Staphylococci
 Genus: Streptococci
 Genus Clostridium
 Fungi:
 Genus: Candida
 Parasite:
 Ectoparasitic skin infection
 by Sarcoptes scabei, variety hominis
Introduction

 Staph infections are caused by Staphylococcus bacteria,

types of germs commonly found on the skin or in the nose
of even healthy individuals. Most of the time, these
bacteria cause no problems or result in relatively minor
skin infections.
Contd..

 But staph infections can turn deadly if the bacteria invade

deeper into your body, entering your bloodstream, joints,
bones, lungs or heart. A growing number of otherwise
healthy people are developing life-threatening staph
infections.
Staphylococcus

 Gram positive bacteria that are small, round (cocci) and

occur as clusters appearing like a bunch of grapes.

 ‘Staphyle’ in Greek means ‘Bunch of grapes’ ‘kokkos’ – means

Berry

 S. aureus was discovered in Aberdeen, Scotland in 1880 by

the surgeon Sir Alexander Ogston in pus from surgical
abscesses.
Contd..

 More than 20 species of Staphylococci are identified but,

only Staphylococcus aureus and Staphylococcus
epidermidis are significant in their interactions with
humans.

 S. aureus colonizes mainly the nasal passages, but it may

be found regularly inmost other anatomical locales while, S.
epidermidis is an inhabitant of the skin.
Contd..

Common species:
• Staphylococcus aureus
• Staphylococcus epidermidis
• Staphylococcus saprophyticus
 Staphylococcus aureus ~ Gram Staphylococcus aureus: As seen
Stained. Staphylococcus aureus are under electron Microscope..
Gram Positive Organisms, hence they
are stained violet. Observe their
characteristic “Grape clusters”
arrangement.
 Growth Characteristics on Culture Media
Yellow pigmented colonies on a Nutrient agar
plate
Contd..
 Staphylococcus is a germ normally found on the skin or inside the
nose of many people.

 Most people with Staph on their skin or in their nose have no

symptoms.

 Because staph can easily enter a cut or scrape, it is a common cause

of skin infections.
Virulence factors

 S. aureus causes disease by multiplying in tissues and causing

inflammation, and also by liberating toxin.
 S. aureus produces several virulence factors, which include the
following:
(a) Cell wall associated proteins and polymers
(b) Extracellular enzymes
(c) Toxins
Cell wall associated proteins and
polymers
 These include capsular polysaccharide, protein A, peptidoglycan,
and teichoic acid that contribute to pathogenesis of
staphylococcal diseases.
 Capsular polysaccharide: Few strains of S. aureus are capsulated.
 These strains are more virulent than the noncapsulated ones.
 The capsule protects the bacteria from phagocytosis.
 The capsule also facilitates adherence of the cocci to host cells
and to prosthetic implants.
 Protein A: Protein A is an important virulence factor since
it has non-specific interaction with Fc portion of the
immunoglobulin G (IgG) leaving the Fab portions free to
combine with specific antigen.
 It is chemotactic, anticomplementary, and
antiphagocytic.
 It causes platelet injury and elicits hypersensitivity
reactions.
Contd..

 Peptidoglycan: It activates the complement, stimulates

production of the antibodies, and inhibits chemotaxis by
inflammatory cells.

 Teichoic acid: It mediates attachment of Staphycocci to

mucosal cell.
What does S. aureus cause?

 Local Pyogenic Infections

 Systemic Infections

 Toxin Mediated Infections

Clinical Syndromes

 The diseases caused by S. aureus can be divided into

two groups:
 (a) inflammatory and
 (b) toxin-mediated staphylococcal diseases.
Inflammatory staphylococcal
diseases
 Staphylococcal skin infections include impetigo, folliculitis,
furuncles, carbuncles, paronychia, surgical wound infection,
blepharitis, and postpartum breast infection.
 S. aureus is the most common cause of boils. The infection is
acquired either by self-inoculation from a carrier site, such as
the nose or through contact with another person harboring
the bacteria.
 Bacteremia and septicemia may occur from any localized
lesion, especially wound infection or as a result of intravenous
drug abuse.
Contd..

 S. aureus is an important cause of acute bacterial endocarditis,

of normal or prosthetic heart valves, which is associated with
high mortality.
 S. aureus is the most common cause of osteomyelitis in children.
The bacteria reach bone through blood stream or by direct
implantation following trauma.
 S. aureus causes pneumonia in postoperative patients following
viral respiratory infection, leading to empyema; it also leads to
chronic sinusitis.
 S. aureus causes deep-seated abscesses in any organ after
bacteremia.
Local infections
Abscess formation is a hallmark of Staph infection.

Staphylococcal skin lesions are centered around hair

follicles

 Boils.

 Impetigo

 Cellulitis

 Staphylococcal scalded skin syndrome.

What are the symptoms?

 Skin infections caused by staph are usually red and painful.

Some start as a painful bump that seems like a spider bite,
but quickly become an abscess (boil) filled with pus and
germs.
1. Furuncle/ Boil

 Focal, suppurative inflammation

of the skin and subcutaneous
tissues.
 Most frequently seen in moist
hairy areas (face, axillae and
groin).
2. Carbuncle
 Collection of furuncles

3. Impetigo
 Highly contagious
 Mainly affects infants
and children
4. Staphylococcal scalded skin syndrome
 Staphylococcal scalded skin
syndrome (SSSS) is a serious skin infection
caused by the bacterium Staphylococcus
aureus.

 This bacterium produces an exfoliative toxin

that causes the outer layers of skin to blister
and peel
5. Cellulitis
 It is a painful bacterial skin infection.
 It may first appear as a red, swollen
area that feels hot and tender to the
touch.
 The redness and swelling can spread
quickly.
 It most often affects the skin of the
lower legs, although the infection can
occur anywhere on a person's body or
face.
How does staph spread?
 Touching skin-to-skin can spread staph from one
person to another.

 Staph can be picked up from surfaces that are

often touched, like phones or doorknobs.

 Sometimes shared personal items, like towels,

soap, or sports equipment can spread staph.

 Pus from an abscess is especially contagious on

skin or surfaces.
Laboratory Diagnosis

 Gram stain

 Culture

 Biochemical analysis
How can I avoid staph
infections?
 Wash your hands regularly with soap and water or hand
sanitizer.

 Use your own towels, soap, and other personal items; do

not share these.
Streptococcal skin
infections
Introduction- Morphology

• Gram positive cocci arranged in

chains.
• Human /animal normal flora
• Some are human pathogens
Classification

1. Based on oxygen requirement

 Obligate anaerobe , Eg :- Peptostreptococci
 Facultative anaerobe
2. Hemolytic property , facultative anaerobic streptococci
classified
 Alpha hemolytic [greenish]
 Beta hemolytic [golden yellow]
 Gamma/non hemolytic streptococci [no color]
Contd..

Based on beta hemolysis, streptococci are classified

serologically into groups based on the nature of
carbohydrate [c]antigen present on cell wall by Lancefield
of known as Lancefield groups.
 20 groups
 Group A is known as Streptococcus pyogenes, which
causes the majority of human infections.
Virulence factors

 Hemolysins
 Pyrogenic exotoxin
 Streptokinase
 DNAase
 Hyaluronidase
Pathogenicity

 Str. Pyogenes causes a variety of suppurative

infections of the skin, including infections of
wounds and burns.
 The two typical streptococcal infections of the
skin are erysipelas and impetigo
Clinical manifestations

NAME OF DISEASE:
1. Invasive (cellulitis)
a. Erysipelas
b. Puerperal fever
c. Surgical scarlet fever
d. Myositis
e. Necrotizing fasciitis
Contd..

2. Localized
a. Impetigo
b. Ecthyma - hardbase
c. Hidradenitis
Contd..

ETIOLOGICAL AGENT: Streptococcus pyogenes

 All beta-hemolytic streptococci are grouped from A to U based

on the C-antigen (Lancefield classification).

 Most human diseases are due to group A organisms but few can
be caused by members of group B, C and G also.

 A pus-generating infection of the skin or mucous membranes.

Surgical wounds are often infected by this organism as well as the
uterus after childbirth.
 Contd..
PATHOLOGY:
Pathology is the result of toxin production:
1. Streptolysin - two types (S and O). They kill leukocytes, lyse RBC's and destroy
heart tissue.
2. Streptokinase - a plasma activator that initiates the fibrinolytic dissolution of
fibrin clots.
3. Hyaluronidase
4. Erythrogenic toxin - produces the generalized erythematous rash of scarlet
fever.
5. Streptodornase - DNAase
6. NADase
7. Exotoxin A - a super antigen which causes over production of cytokines
8. Cysteine protease (Exotoxin B)
Contd..

 Pyoderma strains of S. pyogenes can colonize or survive on

normal skin surfaces for extended periods.

 Epidermal carriage or acquisition appears to be the initial

event predisposing to the development of impetigo in some
patients.

 Following acquisition on the normal skin, minor trauma may be

a prerequisite for initiating infection.
MANIFESTATIONS:
1. Invasive infections (cellulitis)

A. Erysipelas - portal of entry is the skin or outer mucous membrane.

Erysipelas is characterized by acute toxicity; the typical lesion is a raised,

demarcated, bright red area of dermal and subcutaneous inflammation
which advances as the disease progresses.

B. Puerperal fever - uterus is infected

C. Surgical scarlet fever - surgical wound is infected

D. Myositis - muscle is destroyed

E. Necrotizing fasciitis - muscle sheath is destroyed

Erysipelas

• Erysipelas is a diffuse infection involving the

superficial lymphatics
• The affected skin will be swollen and sharply
demarcated from the surrounding healthy area
• Rare and seen only in older patients
Scarlet fever

 Scarlet fever is a rash most commonly associated with

bacterial pharyngitis in school-age and adolescent
children.
 It is a blanching, papular rash that is classically described
as a “sandpaper” rash.
 It generates an exotoxin mainly responsible for the skin
manifestation of the infection
Scarlet fever
Necrotizing Subcutaneous Infection
(Necrotizing Fasciitis)

 “Flesh Eating Strep” Streptococcus pyogenes (Group A β

hemolytic Streptococci (GABHS) is the causative agent

 The disease starts as localized infection that rapidly

spreading cellulitis with necrosis (skin and deeper fascia;
may involve muscle).

 Begin with fever, systemic toxicity and severe pain

Contd..

 The development of a painful, red swelling that rapidly

progress to necrosis of the subcutaneous tissue and
overlying skin.

 The Invasive & spreading cellulitis may lead to loss of limb

 May lead to toxic shock

2. Local infections (pyodermas)

A. Impetigo - infection of superficial layer of skin in small

children.

 Brown crust on skin is major symptom.

 The typical lesions of impetigo are crusted and vesicular.

 Systemic manifestations are minimal or absent.

 The lesions begin as vesicles with little erythema.

 They rapidly progress to pustules that are subsequently covered

with thickened, yellow crusts, with thin pus beneath.
Contd..

 Such lesions commonly occur over exposed areas,

especially on the extremities.

 Itching is frequent.

 Urticaria or erythema multiform occasionally develops.

 Transient lymphadenitis occurs, and significant regional

lymphadenopathy is characteristic of streptococcal
impetigo.
Impetigo

• Found mainly in young children

• Usually appears as red sores especially
around nose and mouth
• On progression, the sores burst and
develop into honey colored crusts
Impetigo

 The initial lesion of streptococcal impetigo is a vesicle in

the superficial epidermis; capillary dilation and infiltration
with leukocytes occurs in the upper cutis.

 Older lesions are frankly purulent and ecthyma is

characterized by an ulcer with thickened margins.
Contd..

 Lymphatic channels and regional lymph nodes are

involved; lymphangitis is more common in cellulitis and
deeper wound infections.

 Bacteremia may result from pyoderma, but it is more

likely in erysipelas or deeper, suppurative infection.
Contd..

B. Ecthyma: Ecthyma is an ulcerative form of impetigo.

 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 immunocompromised individuals.
Ecthyma
Contd..

 Hidradenitis suppurativa is a skin condition that causes

small, painful lumps to form under the skin.

 The lumps can break open, or tunnels can form under

the skin.

 The condition mostly affects areas where the skin rubs

together, such as the armpits, groin, buttocks and
breasts.
Hidradenitis
DIAGNOSIS:

 The etiologic diagnosis of streptococcal pyoderma is

confirmed by the isolation of S. pyogenes in cultures of
material from typical lesions.

 Underlying skin diseases that predispose to streptococcal

pyoderma, such as tinea capitis and eczema, may
become more apparent.
Laboratory Diagnosis

 Diagnosis of acute suppurative infections is made by

bacterial culture, non suppurative complications
diagnose by demonstration of antibodies

 Gram staining

 Culture- BA at 370c for 24hrs

 Biochemical reactions
Thank you