Eye and skin infections

What kind of defense is the skin?

A great physical defense

Is the skin prone to infection?

Yes

What are most skin infections considered?

Most are local infections and non-life-threatening

What are the layers of the skin?

Epidermis, dermis, hypodermis

Epidermal stratum corneum

• Relatively thin- Rich in keratin- Waterproof

Shedding

Desquamation (can shed microbes)

What are the two types of glands in the skin?

Sweat glands and sebaceous glands

What does perspiration provide?

Moisture

What 3 things are in sweat?

Salt, lysozyme, and AMP

Is everyone's skin microbiome the same? Why or why not?

No, composition varies by person

True or False: Moist skin has different makeup than dry skin

True

What else can be present in the skin microbiome? (Other than bacteria)

Some viruses and fungi also present in the skin microbiome

Where is MRSA located?

Residence inside nares

What skin is unaffected by MRSA? What is at risk?

• Healthy skin unaffected- Open wounds at risk

Where is MRSA common?

Common in hospitals/healthcare

What does injury allow?

Allows microbes access to more nutrients

What can microbes cause? (Think: cuts, etc.)

• Can cause a variety of skin lesions- Some of them look very similar

What are the types of skin lesions? (There are 8)

-Crust- Cyst- Macule- Papule- Pustule- Ulcer- Vesicle- Wheal

Staphylococcus aureus

• Highly contagious - skin-to-skin contact- Prevalent in community settings- Antibiotic resistance common & a problem (MRSA)

How can S. aureus be transmitted?

Nasal carriers transfer to hands, then to fomites or others

How is antibiotic resistance measured? How is it treated?

• Measure antibiotic sensitivity- Often treated with TMP/SMZ, tetracycline, or linezolid

Staphylococcal virulence

• Can be positive for coagulase to help with abscess formation- Inhibit phagocytosis by binding antibodies

Staphylolysins

Cytotoxic for multiple cell types

Leukocidins

• Kill white blood cells and help form pus- Some produce toxins

What two things help identify causative agents?

Wound sampling and culture

What are the two types of species of Staphylococcus? (Think: positive and negative)

• Coagulase-positive species (CoPS)- Coagulase-negative species (CoNS)

What are CoPS likely to cause? Where are CoNS prevalent?

CoPS more likely to cause human disease, but CoNS prevalent in critical/semi-critical items

What are coagulase-positive species typically assumed to be?

S. aureus

How are coagulase-positive species identified? (Think: testing)

Passive agglutination testing

Purulent skin infections

Have pus

Staphylococal scalded skin syndrome

• Commonly seen in infants (S. aureus)- Red skin- Severe peeling- IV antibiotics

Impetigo (+ 2 species)

• Characteristic pustules or blisters around the nose and mouth- S. aureus or S. pyogenes

How is impetigo treated?

Treatment using topical or oral antibiotics

Streptococcus Infections

• Distinguished by surface carbohydrates- Group A streptococcus: S. pyogenes

S. pyogenes

• Produces streptolysin O & S, hyaluronidase, streptokinase- Aid in transmission & stimulate inflammation- Capsule & M protein to avoid phagocytosis- Wide variety of diseases

What are some common streptococcal infections?

• Cellulitis- Necrotizing fasciitis- Pseudomonas infections come from water and soil

Necrotizing fasciitis (LONG RESPONSE)

• Also caused by Klebsiella, Clostridium, E. coli, S. aureus- Fascia becomes infected after overcoming host defenses- Bacterial proteases destroy tissues & prevent neutrophil migration- Not always skin infection, can be unknown/blunt force trauma

What kinds of pseudomonas infections come from water and soil?

• Phospholipase C- Exoenzyme S- Exotoxin A

What is anthrax caused by?

Bacillus anthracis

What does anthrax infect?

Mainly infects animals, but endospores can cause disease in people

What does cutaneous anthrax create?

Black eschar, death ~20%

Anthrax exotoxins

• Protein antigen & enzymatic lethal factor to form LeTX- Also EdTX, edema toxin

Anthrax mortality (GI and respiratory)

• GI ~ 40%- Respiratory ~45-85%

How is anthrax a biological weapon?

Mail order anthrax killed 5 of 11 people in 2001

Papillomas

• Warts- Commonly human papillomavirus (HPV)- Variety of presentations on skin- Strong immune system rid skin of warts, otherwise, removal or topicala

What else can HPV cause?

Oral herpes

Where do HPV warts present on the skin? (Think: areas of the body)

Feet, face, hands

What does the lacrimal gland secrete?

Tears

What is the function of the lacrimal puncta?

Drainage for tears

What is in the nasolacrimal duct?

Defensins and lactoferrin

What do lysozymes in the nasolacrimal duct do?

Prevent colonization

Surface and inner eyelid

Mucous membranes aka conjunctiva

What size is the microbiome in the inner eye?

SMALL microbiome (~12 genera)

The use of what can cause microbiome changes in the eye?

Contact lens use

What in the inner eye is always sterile?

Vitreous humor

Conjunctivitis

Commonly pink eye

Are deeper infections common in the eye?

No

Blepharitis

Eyelid inflammation

Keratitis

Corneal inflammation

What can conjunctivitis lead to? (Think: symptoms)

Pus formation and bleeding

What is the most common cause of conjunctivitis?

Viral infection

What 3 things can be irritants/inflammatory mediators?

Allergens, pollutants, and chemicals

What is bacterial conjunctivitis most often caused by?

Haemophilus influenzae

Does bacterial conjunctivitis resolve on its own?

Usually, but antibiotics may be necessary

Who is at risk for bacterial conjunctivitis?

Contact users

Neonatal conjunctivitis

May be transferred during birth, especially gonorrhea & chlamydia

Trachoma

• Granular conjunctivitis- Cause of preventable blindness - rare in the US- Chlamydia trachomatis- Forms necrotic follicles & scarring in upper eyelid- Antibiotics help if treated early

What is keratitis caused by?

S. aureus or P. aeruginosa

What is keratitis common in?

Contact users

What does keratitis cause?

Blindness