Chapter 19: Microbial Diseases of the Skin and Wounds

What are some functions of the skin?

• Prevents excessive water loss

• Regulates temperature

• Involved in sensory phenomena

• Vitamin D formation

• Barrier against microbial invaders

The skin is composed of these two main layers:

Epidermis & Dermis

Wounds

Trauma to any tissue of the body. Ex. Cuts, scrapes, surgery, burns, and bites. Can be fatal.

Skin Microbiota

Normally harmless microbes present on the skin. Grow in moist areas. Cannot be completely removed through cleansing.

Skin microbiota is made up of various microbes such as

Yeast and Bacteria, which may produce disease if immune system is suppressed or penetrated epidermis.

What are the general characteristics of Staphyloccocus ?

A facultative anaerobe, meaning it can survive without oxygen but growth is slow.

Tolerant of salt and desiccation or drying.

Which two species is commonly found on skin?

Staphylococcus aureus and Staphylococcus epidermis

Which species that is commonly found on skin is not restricted to only skin?

Staphylococcus aureus

Pyogenic

Produces pus, mix of dead tissue and bodily fluids.

What are the virulence factors for Streptococcus pyogenes?

Hyaluronidase

Streptokinase

Exotoxin A

Streptolysin S

M protein

Hyaluronidase

Dissolves intercellular cement. Helps hold cells together, physical barrier.

Streptokinase

Dissolves blood clots.

Exotoxin A

Triggers inflammation that causes more tissue damage.

Streptolysin S

Kills many types of human cells including neutrophils.

M Protein

Allows bacteria to attach to nose and throat cells, allows bacteria to survive phagocytosis.

Folliculitis

Causative agent: Staphylococcus aureus

Classification: Low G+C Gram Pos.

Signs/Symptoms: furuncles or boils, carbuncles

Pathogenesis: Staphylococcus aureus

Epidemiology: transmitted via direct contact, fomites

Diagnosis: isolate of gram-positive bacteria in grape like clusters from pus.

Treatment: Mupirocin, Dicloxacillin, Vancomycin

Prevention: hand antisepsis, proper procedures in hospitals

Scalded Skin Syndrome

Causative agent: Some staphylococcus aureus strains

Classification: Low G+C Gram pos.

Signs/Symptoms: Skin is red, wrinkled, blistered, outer epidermis peeled.

Pathogenesis: Certain strains cause exfoliative toxins.

Epidemiology: primarily in infants, person to person.

Diagnosis: sloughing of skin.

Treatment: antimicrobial drugs

Prevention: Widespread of staphylococcus aureus makes prevention difficult.

Impetigo

Causative agent: some caused by streptococcus pyrogens. Most cases caused by Staphylococcus aureus.

Classification: Low G+C Gram pos.

Signs/Symptoms: red patches form on face and limbs.

Pathogenesis: bacteria invade where skin is comprised.

Epidemiology: person to person, fomites. Most common in children

Diagnosis: presence of vesicles.

Treatment: oral or topical antimicrobials and cleaning the area.

Prevention: proper hygiene and cleanliness.

Erysipelas

Causative agent: most cases caused by Staphylococcus aureus and some by streptococcus pyrogens.

Classification: Low G+C Gram pos.

Signs/Symptoms: infection spreads to lymph nodes.

Pathogenesis: bacteria invade where is compromised.

Epidemiology: person to person via fomites, mostly in ederly

Diagnosis: visual examination of skin.

Treatment: penicillin

Prevention: proper hygiene and cleanliness.

Necrotizing Fasciitis

Causative agent: Streptococcus pyrogens

Classification: Low G+C Gram Pos.

Signs/Symptoms: redness, pain, swelling, fever.

Pathogenesis: can be fatal. Can enter through skin.

Epidemiology: person to person, death in 20% of patients.

Diagnosis: Early diagnosis is difficult, non specific symptoms.

Treatment: Clindamycin and penicillin

Prevention: difficult to prevent. Very common

Acne

Causative agent: Propionibacterium acne’s

Classification: High G+C Gram Pos.

Signs/Symptoms: whiteheads, blackheads, pustule formation

Pathogenesis: interaction of host factors

Epidemiology: found on skin, begins in adolescence but can be later.

Diagnosis: visual examination

Treatment: antimicrobial drugs, accutane, uv light

Prevention: topical treatments and keep clean

Gas Gangrene

Causative agent: several clostridium species

Classification: Low G+C gram pos. Endospore.

Signs/Symptoms: blackening of infected gas bubbles.

Pathogenesis: negative cells secrete 11 toxins.

Epidemiology: traumatic event introduces spores. Mortality rate is 40%.

Diagnosis: by appearance

Treatment: rapid and surgical removal of dead tissue, antimicrobials

Prevention: proper cleaning of wounds.

Herpes

Causative agent: human herpes viruses 1 & 2

Classification: ds DNA, herpesviridae family.

Signs/Symptoms: slow spreading lesions, reoccurrence is common.

Pathogenesis: produces proteins, virulence factors

Epidemiology: spread between mucous membranes mouth and genitals.

Diagnosis: presence of characteristic lesions.

Treatment: chemotherapeutic drugs but no cure.

Prevention: healthcare workers wear gloves to limit exposure.

Measles

Causative agent: measles virus

Classification: negative sense, single strand RNA virus.

Signs/Symptoms: fever, runny nose, cough, conjunctivitis, kopliks spots

Pathogenesis: immune response to infected cells cause most symptoms.

Epidemiology: highly contagious via respiratory droplets. Humans are the only host.

Diagnosis: based on signs of measles including rash, koplik spots, fever.

Treatment: Vitamin A, antibodies, ribavirin, supportive, no antiviral drug.

Prevention: MMR vaccine (2 doses)