It can be caused by Exfoliative toxin A. The phyogenic superficial infection can be divided into two other subdivisions; Impetigo, and non-bullous impetigo. Bullous impetigo is caused by Staphylococcus aureus, which produces exfoliative toxins, whereas non-bullous impetigo is caused by either Staphylococcus aureus, or Streptococcus pyogenes. Bullous Impetigo can cause deaths in fewer than 3% of infected children, but up to a 60% death rate in adults. 30% of all Impetigo cases are related to Bullous impetigo.
S. aureus Pathogenesis
A phyogenic non-motile Gram-positive cocci which forms into grape like clusters. Just like other forms of staph, S. aureus has a variety of virulence factors which include surface proteins involved in adherence, secretion of enzymes that degrade proteins, and secrete toxins which damage the host’s cells. S. aureus expresses surface receptors for fibrinogen, fibronectin, and vitronectin. These surface receptors allow a bridge to be formed which binds to host endothelial cells. Lipases allow for the degradation of lipids on the skin surface and its expression can be directly correlated with its ability of the bacteria to produce abscesses.
Bullous impetigo Pathogenesis
Exfoliating toxins are serine proteases that specifically bind to and cleave desmoglein 1 (Dsg1). Previous studies suggested that exfoliating toxins bind to gangliosides, causing a release of protease by keratinocytes acting as superantigens in stimulating the skin’s immune system. A more recent proposal states there are three known exfoliating toxins; ETA, ETB, and ETD which act as a glutamic acid-specific serine protease with concentrated specificity. Which results in the cleavage of human Dsg1 at a unique site after glutamic acid residues causing deactivation. Proteolysis of the peptide bond leading up to the dysfunction of Dsg1 and the desmosome allows for an understanding as to why the bullous forms, making the peptide bond crucial for proper function if Dsg1.
Bullous impetigo can appear around the diaper region, axilla, or neck. The bacteria causes a toxin to be produced that reduces cell-to-cell stickiness (adhesion), causing for the top layer of skin (epidermis), and lower layer of skin (dermis) to separate. Vesicles rapidly enlarge and form the bullae which is a blister more than 5mm across. Bullae is also known as Staphylococcal scalded skin syndrome. Other associated symptoms are itching, swelling of nearby glands, fever and diarrhea. It should also be noted that pain is very rare.
Long-term effects: Once the scabs on the bullous have fallen off, scarring is minimal. Possible long-term effects are kidney disease.
Observing the skins physical appearance, or swabbing a culture of the lesion for S. aureus. Nasal swabs from the patient’s immediate family members are necessary to identify them as being asymptomatic nasal carriers of S. aureus.
- insect bites
Uncommon Bullous with other variants
Where outbreaks can occur
Hospital wards and, nurseries, and can be passed from person to person. Also many close contact sports. Therefore, it is advised that the patient has to try to limit as much human contact as possible to limit transmission of infection.
After 48 hours the disease is considered no longer contagious assuming the proper antibiotic treatments have been administered. Antibiotic treatment typically last 7–10 days, and although highly effective some cases of Methicillin resistance S. aureus/MRSA may require longer therapy depending on the severity of infection and how much it has spread.
Antibiotic creams are the preferred treatment for mild cases of impetigo, despite their limited systemic absorption. Such prescribed ointments include Neosporin, Fusidic Acid, Chloramphenicol and Mupirocin. More severe cases of impetigo however (especially bullous impetigo) will likely require oral agents with better systemic bioavailability, such as cephalexin. Cases that do not resolve with initial antibiotic therapy or require hospitalization may also be indicative an MRSA infection, which would require the use of agents specifically able to treat it, such as clindamycin.
Since the common pathogens involved with impetigo are bacteria naturally found on the skin, most prevention (especially in children), is targeted towards appropriate hygiene, wound cleaning, and minimizing scratching (i.e. by keeping nails trimmed and short). Avoiding close contact and sharing of items such as towels with potentially infected individuals is also recommended.
Histology of normal epidermal tissue through H&E. Composed of four layers, Stratum basale, Stratum spinosum, Stratum granulosum, and Stratum corneum. Normal pathology of the skin, displaying the dermis which is attached to underlying loose connective tissue which subsequently contains primary adipose tissue.
Histology of Bullous Impetigo through H&E. The cleavage plane can be found either subcorneal or within the upper stratum granulosum. The roof of the pustule is parakeratotic stratum cirneum, and the floor is formed of keratinocytes, which may or may not be acantholytic. Neutrophils begin to fill the pustule. Toxins are produced by S. aureus and target desmoglein, which is a desmosomal cell-cell adhesion molecule that is found in the upper levels of the epidermis. Stratum Lucidum is no longer present and can be seen infiltrated with inflammatory cells. This correlates with the subcorneal localization of the bullae.
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