Lecture 7: Skin and Soft Tissue Infections Flashcards
What is the main function of the epidermis in the skin?
To act as a physical barrier against infection.
Describe the composition of the skin epidermis.
Several layers of tightly packed epithelial cells. The outer layers (closest to the surface) are dead and keratinised, giving them additional strength.
Describe the composition of the skin dermis.
Made up of connective tissue, blood vessels, hair follicles sweat glands and sebaceuos glands. The sebaceous glands produce sebum, which contains lactic and fatty acids. This maintains skin at pH 3-5, inhibiting microbial growth.
Outline the key steps of the inflammatory response to a local skin trauma.
- Damaged tissues release histamines which cause localised vasodilation, increasing blood flow to the area (redness and heat).
- Walls of capillaries become more permeable, allowing plasma, white blood cells, and proteins to leak into the surrounding tissue. - This causes swelling (oedema).
- Neutrophils and macrophages attracted to the site of injury by chemotaxis, where they engulf and digest pathogens (phagocytosis).
- Accumulation of dead pathogens, white blood cells, and tissue debris forms pus.
Which type of microorganism causes the majority of skin and soft tissue infections?
Bacteria
Give 7 risk factors that may result in more severe skin and soft tissue infections?
- Diabetes (microorganisms thrive on the sugar)
- Critical illness
- Elderly age
- Immunocompromised state
- Liver disease
- Kidney disease
- Vascular insufficiency
What is an erysipela?
A skin infection that can also affect the superficial layers of soft tissue. It can spread to the lymphatic system, resulting in secondary infections. It presents as red rashes, more commonly on the face or legs
What are the 3 main examples of mild skin infections that I should know, from least to most severe?
- Folliculitis (pimples)
- Furuncles (boils)
- Carbuncles (abscesses). Typically self-contained and don’t require antibiotics; involve pus.
How are erysipelas and cellulitis treated?
Topical antibiotics: IV antibiotics for more severe infections. Diagnosis is necessary for effective treatment.
Why is bacteraemia so dangerous?
We have a very low tolerance for microbes in the bloodstream. Infection can become systemic, meaning that it can colonise, causing secondary infections elsewhere in the body - very difficult to treat.
What is a biofilm?
An aggregate of microorganisms attached to a surface or each other, embedded in a self-produced matrix of sticky substances like polysaccharides and proteins, making them more resistant to treatment.
Systemic infections affect tissues around the body. Why are they so dangerous to humans?
Can cause the toxic-Shock Response (an inappropriately big immune response, resulting in a cytokine storm, give rise to significant tissue damage). Drugs can reduce immune response, but difficult to balance against ensuring the immune system is still able to fight the infection. THey can also cause secondary infections.
What is osteomyelitis?
Chronic infection of the bone.
Where are Candida fungi generally found?
Variety of locations around the body, particularly moist areas of the skin, the oral mucosae and GI mucosae.
Describe the 3 different morphologies of C. albicans.
- Commensal (yeast cells).
- Pseudohyphae.
- Pathogenic (Hyphae).
How do hyphae invade host tissues?
Either between cells or by producing the toxin: Candidalysin which it uses to scavenge nutrients.
What are 2 examples of candidal skin infections?
- Interdigital candidosis (white plaques in between fingers), generally superficial.
- Oral candidosis (more common in people who have dentures, generally only significant in immunocomprimised individuals).
What are 3 examples of viral skin infections and how are they treated?
- Chickpenpox
- Hand foot and mouth (Coxsackievirus)
- Mollescum contagiosum.
Generally self-resolving with minimal issues.
How does Toxic-Shock Sydrome occur and how is this beneficial to the bacteria?
Tsst-1 superantigen upregulates the inflammatory response - meaning that antigen not required for signal transduction. Beneficial: Inflammation leads to cell lysis (release of contents for nutrients)
Streptococcus pneumoniae produce pneumolysin toxins. What type of toxins are these and what are the negative implications for the bacteria when producing these toxins?
There are pore-forming toxins, causing leakage from host cell. Streptococcus pneumoniae must produce this in order to adhere to hosts but if hosts cannot function, bacteria cannot survive.
Fungi produce mycotoxins which are secondary metabolites. What does this mean?
They don’t need to produce these toxins in order to survive and grow, but there is a benefit e.g. adhesion / lysis of host for nutrients.
Candida produce candidalysin when in its hyphae form. What is the mechanism of action of this toxin?
Pore-forming peptide toxin that causes influx of Calcium ions. Activates EGFR pathway, causing host to produce lots of pro-inflammatory mediators. Neutrophils are recruited but they cannot engulf hyphae.
How can bacterial SSTIs be treated generally?
Bactericidal antibiotics (actively kill bacteria cell), Bacteriostatic antibiotics (stop bacteria from proliferating).
How are fungal SSTIs treated?
Antifungals - can be topical, IV or ingested. We only have 4 different classes of antifungals though…
What is prophylaxis?
Measures taken to prevent disease or infection before it occurs.
What is neutropenia?
Abnormally low levels of neutrophils. It increases the risk of bacterial and fungal infections.
Some fungi produce mycotoxins. What are the 4 main families of mycotoxins mentioned in the lecture?
Aflatoxins, Gliotoxins, Ochratoxins, Fumonisin.
