Chapter 21: Skin and Eye Infections

Genus Staphylococcus

• Normal flora of the skin and mucous membranes

• Spherical cells arranged in irregular clusters

• Gram-positive

• Catalase-positive

• Lack spores and flagella

• May have capsules

Examples:

• S. epidermidis and S. hominis (Normal skin flora)

• S. aureus (Skin/nasal passages)

Staphylococcus Aureus

• Well-defined virulence factors

  • Exoenzymes and toxins

• Highly resistant

  • Survive in harsh conditions; high salt, desiccation, etc.

• High carriage rate; easily transmissible

  • High contagious; skin to skin, nose → hands → fomites

• Culture (for ID): catalase-positive, coagulase-positive, mannitol fermentation-positive, high salt tolerance.

• Superficial Infections of the skin:

  • Furuncles, carbuncles, impetigo, scaled skin syndrome

Conjunctivitis

Is inflammation of the conjunctiva

Blepharitis

Is inflammation of the eyelids

Keratitis

Is inflammation of the cornea.

Keratoconjunctivitis

Inflammation of both the cornea and the conjuctiva

S. aureus

Most common cause of pyrogenic infection of the skin.

• Furuncles, carbuncle, acne.

Impetigo

Pathogen: Staphylococcus aureus, S. pyogenes.

Signs: vesicles, pustules, or bullae that rupture, producing encrusted sores.

Transmission: Highly contagious through contact

Staphylococcal scalded skin syndrome (SSSS)

Pathogen: S. aureus

Signs and Symptoms: Erythema and severe peeling of skin.

Transmission: Infection of skin and mucous membranes, especially in children.

Coagulase-negative staphylococci

Frequently involved in nosocomial and opportunistic infections.

• S. epidermidis

• S. saprophyticus

All may cause wound infections by penetrating through broken skin.

S. epidermidis

Lives on the skin and mucous membranes; endocarditis, bacteremia, UTI

S. saprophyticus

Infrequently lives on the skin, intestine, and vagina; UTI

Clinical Concerns and Treatment for Staphylococci

• 95% have penicillinase (Beta-lactamase) and are resistant to penicillin and ampicillin.

• MRSA - Methicillin-Resistant S. aureus

• VRSA - Vancomycin-Resistant S. aureus

  • HAI/Community Acquired

• Abscesses have to be surgically perforated

• Systemic infections require intensive lengthy therapy.

Prevention of Staphylococcal infections

• Universal precautions by healthcare providers to prevent nosocomial infections.

• Hygiene and cleansing

  • Handwashing

Genus Streptococcus

• Gram-positive spherical/ovoid cocci arranged in long chains

• Non-spore-forming, nonmotile, can form capsules and slime layers.

• Facultative anaerobes (peroxidase system present).

• Well-defined virulence factors

• Sensitive to drying, heat, and disinfectants.

• Can be classified based on hemolysis

Cellulitis

Pathogen: Streptococcus pyogenes

Signs/symptoms: painful, red rash

Transmission: Cut or abrasion

Erysipelas

Pathogen: S. pyogenes

Signs/Symptoms: raised rash, usually with clear borders.

Transmission: cut or abrasion

Erythema nodosum

Pathogen: S. pyogenes

Signs/Symptoms: red lumps or nodules, typically on lower legs.

Transmission: Associated with other streptococcal infection.

Necrotizing Fasciitis

Pathogen: S. pyogenes, Klebsiella, Clostridium, others.

Signs/Symptoms: infection of fascia and rapidly spreading tissue death; can lead to septic shock and death.

Transmission: cut or abrasion.

Exotoxin

A produced by S. pyogenes that acts as a superantigen.

Pseudomonas aeruginosa

“We love water”

• Common inhabitant of soil and water and human skin

• Resistant to soaps, dyes, quaternary ammonium, disinfectants, drugs, and drying.

• Opportunistic pathogen

• Common cause of nosocomial infections in hosts with burns, neoplastic disease, cystic fibrosis.

• Grapelike odor and greenish-blue pigment (pyocyanin)

• Multidrug resistant - antibody resistant.

Otitis externa

Pathogen: Pseudomonas aeruginosa

Signs/Symptoms: inflammation of the outer ear and ear canal can lead to painful swelling.

Transmission: enters ear canal via pool or other water.

Acne

Pathogen: Propionibacterium acnes

Signs/Symptoms: Comedones

Transmission: Not transmissble

Comedones

Non-inflammatory acne

Genus Bacillus

• Gram-positive, endospore-forming, motile rods.

• Mostly saprobic

• Primary habitat is soil

• 2 species of importance

  • Bacillus anthracis

  • Bacillus cereus

Saprobic

Dead material

Anthrax (cutaneous)

Pathogen: Bacillus anthracis

Signs/Symptoms: Eschar at site of infection; may lead to septicemia and can be fatal.

Transmission: Endospores through cut or abrasions.

• Least dangerous

Pulmonary Anthrax

Inhalation of spores: respiratory failure

• Bio weapon

• Most dangerous form of anthrax

Gastrointestinal Anthrax

Ingested spores

Injection Anthrax

New outbreak in heroin users.

Eschar

Necrotic tissue

Acute Bacterial Conjunctivitis

Pathogen: Haemophilus influenzae

Sign/Symptom: Inflammation of conjunctiva with purulent discharge.(pink eye)

Transmission: Exposure to secretions from infected individuals.

Neonatal Conjunctivitis

Pathogen: Chlamydia trachomatis, Neisseria gonorrhoeae.

Sign/Symptoms: Inflammation of conjunctiva, purulent discharge, scarring and perforation of cornea; may lead to blindness.

Transmission: Neonate exposed to pathogens in birth canal of mother with chlamydia or gonorrhea.

Trachoma

(granular conjunctivitis)

Pathogen: Chlamydia trachomatis

Signs/symptoms: Chronic conjunctivitis, trichiasis, scarring, blindness.

Transmission: Contact with infected individuals or contaminated fomites; transmission by eye-seeking flies.

Bacterial Keratitis

Pathogen: Staphylococcus epidermidis, Pseudomonas aeruginosa.

Signs/Symptoms: Redness and irritation of eye, blurred vision, sensitivity to light; progressive corneal scarring, which can lead to blindness.

Transmission: Exposure to pathogens on contaminated contact lenses.

Viral Infections

Viruses that use the skin as portal of entry

• Human papillomavirus (HPV)

• Herpesvirus

• Human Parvovirus (Flu)

• Adenovirus → conjunctivitis

Papillomas

Pathogen: Human papillomavirus

Signs/Symptoms: Common warts, plantar warts, flat warts, filiform warts, and others.

• Warts can regress over time or be removed

• Warts can reoccur (Latency)

• Cause persistent infections and tumors

Transmission: Contact with infected individuals or contaminated fomites.

Oral Herpes

Pathogen: Herpes simplex virus 1 (HSV-1)

Signs/symptoms: May cause initial systemic symptoms; cold sores.

Transmission: Highly contagious via direct contact with infected individuals.

• HSV 1 and HSV 2 are potentially fatal in the neonate and fetus

HSV-2

Lesions on the genitalia, possibly the oral cavity.

Herpetic whitlow

HSV-1 or HSV-2 can penetrate a break in the skin of a finger/thumb and cause a localized infection.

Fifth Disease

Pathogen: Parvovirus B19

Signs/Symptoms: May have initial cold-like symptoms; “Slapped cheek” rash.

Transmission: Highly contagious via respiratory secretions of infected individuals.

Roseola

Pathogen: Human herpesvirus 6 (HHV-6), human herpesvirus 7 (HHV-7).

Signs/Symptoms: Initial cold-like symptoms with high fever, followed by a macular or popular rash three to five days later.

Transmission: Spread by viral and respiratory secretions of infected individuals.

Herpes Keratitis

Pathogen: Herpes simplex virus 1 (HSV-1)

Signs/Symptoms: Inflammation of conjunctiva and cornea; irritation, excess tears, sensitivity to light; lesions to blindness.

Transmission: Direct eye contact with discharge from herpes lesions elsewhere in the body or from another infected individual.

Viral conjunctivitis

Pathogen: Adenoviruses and others

Signs/Symptoms: Inflammation of the conjunctiva; watery, nonpurulent discharge.

Transmission: Associated with common cold; contagious via contact with pink eye discharge.

Acanthamoeba Keratitis

Pathogen: Acanthamoeba

Signs/Symptoms: Inflammation and damage to cornea; vision impairment or blindness.

• Difficult to treat.

Transmission: Exposure to pathogens in contaminated water or on contact lenses.

• Prompt treatment is necessary to prevent the condition from progressing

  • pain, redness/irritation, light sensitivity, foreign body sensation, blurred vision.

Cutaneous mycoses

Superficial fungal infections

Subcutaneous mycoses

fungal infections infect deeper tissues

Systemic mycoses

Fungal infection throughout the body.

Tineas

Pathogen: Trichophyton spp., Epidermophyton spp., Microsporum spp.

Signs/Symptoms: Itchy, ring-like lesions (ringworm) at sites of infection.

Transmission: Contact with dermatophytic fungi, especially in warm, moist environments conductive to fungal growth.

Dermatophytes

Fungi that require keratin for growth (skin/hair/nails)

Tinea Corporis

(Ringworm)

Body

Tinea Capitis

(Ringworm)

Scalp

Tinea Pedis

(Athletes foot)

Feet

Tinea Barbae

(Barber’s itch)

Beard

Tinea Cruris

(Jock itch)

Groin

Tinea unguium

(onychomycosis)

Toenails, fingersnails.

Cutaneous Aspergillosis

Pathogen: Aspergillus fumigatus, Aspergillus flavus.

Signs/Symptoms: Distinctive eschars at site(s) of infection.

• Both primary and secondary.

Transmission: Entry via wound (primary cutaneous aspergillosis) or via the respiratory system (secondary cutaneous aspergillosis); commonly a hospital-acquire infection.

Candidasis

Pathogen: Candida albicans

Signs/Symptoms: Intertrigo, localized rash, yellowing of nails.

Transmission: Overgrowth of normal skin microbiota, especially in moist, dark areas.

Candida albicans

Normal flora of the oral cavity, genitalia, large intestine, skin.

Sporotrichosis

Pathogen: Sporothrix schenkii

• Saprobic (dead or alive)

• Dimorphic (mold or yeast)

Signs/Symptoms: Subcutaneous ulcers and abscesses; may spread to large area, e.g., hand or arm.

Transmission: Entry via thorn prick or other wound.

Loiasis

Pathogen: Loa Loa

Signs/Symptoms: Recurring fever and localized Calabar swelling, itching, and skin or eye pain during subcutaneous migration of worms.

Transmission: Larvae transmitted between humans by deerfly vector.