Bacteria, fungi and yeast of skin (part 1) Flashcards
What are the chemical and mechanical defenses of the skin?
- mechanical - keratinocytes, keratin layer, continuous renewal
- chemical - antimicrobial compounds, resident microflora
What is the role of TLRs?
- recognise specific compunds
- activation of TLRs, production of chemokines, attracts immune cells - starts the cascade
What does the innate immune system recognise?
- PAMPs: pathogen associated molecular patterns
- peptidoglycan fragments (bacteria)
- proteins (bacteria)
- nucleic acids (viruses and bacteria)
- cell wall lipids (gram negative bacteria)
- carbs (fungi, bacteria)
- DAMPs: damage associated molecular patterns
- stress-induced proteins (heat shock proteins)
- nuclear proteins
What are some of the normal microbiota of the skin?
- staphylococcus
- s. epidermidis
- s. aureus
- micrococcus
- diptheroids
- malassezia furfur
all of these stop other bacteria colonising
Name some diseases associated with skin infections?
- pruritis (itchy)
- alopecia
- scaling/ crusts
- pyoderma (pustules, superficial or deep)
- erosions, ulcers, pigment disorders, nodules and tumours, sinus tracts
What types of infection can bacteria produce? (2)
- superficial infections
- surface pyodermas and superficial folliculitis
- deep infections
- furunculosis and nodules/ sinus tracts
What are the aetiologies of pruritus?
- allergy
- atopy
- fleas
- arthropods
- food
- contacts
- infectious agents
- staphylococci
- other bacteria
- malassezia
- dermatophytes
- ectoparasites
- sarcoptes
- cheyletiella
- demodicosis
- lice
- trombicula
- others
- neoplasia
- immune mediated
- contact dermatitis
How does alopecia occur?
- bacteria colonise/ infect hair follicle
- infection triggers innate and adaptive immune responses
- folliculitis
- damage to hair shafts
- atrophy
What is this showing? and what are the different coloured dots?
- folliculitis/ sinus formation
- red/ yellow = bacteria
- blue = immune cells
What is pyoderma caused by?
- commonyl caused by staphylococci/ streptococci
- cats, dogs - S. pseudintermedius
- horse, cattle, sheep - S. aureus
- also Group A strepococci
- pasteurella
What are the types of pyoderma?
- superficial
- coagulase + staphylococci
- pasteurella. streptococci
- exudative dermatitis: staphylococcus hyicus, dermatophilus congolenis
- deep (damage)
- subcutaneous abscess
- cellulitis
- necrotising fascitis (rare) < streptococcus canis
How does a pustule form?
- bacteria start growing
- influx of neutrophils
- neutrophils and dead bacteria form the pustule at the surface
Label
What condition does this dog have?
What is this an example of?
- deep pyoderma
What are the characteristics of Staphylococci?
- aerobic/ facultative anaerobic
- gram positive
- catalase positive
What are 2 subtypes of Staphylococci?
- coagulase-negatuce (CoNS, CNS): S.epidermidis
- commensal on skin, opportunisitic pathogen
- coagulase-positive: S.pseudintermedius, S.intermedius, S.aureus
How do you test for MRSA and MRSP?
- MRSA- cefoxitin
- MRSP- oxacillin (false negative with cefoxitin)
What are some virulence factors?
- cell wall polymers - peptidoglycan, techoic acid
- adhesins - Ig-binding
- toxins - enterotoxin
- lysins
- coagulase
- DNase
Describe Strept A
- GAS
- G+ve, catalase +ve, oxidase +ve, beta haemolytic
- Strep pyogenes
- pathology due to release of toxins and aggressins
- streptolysin - S + O
- streptokinase - fibrinolysin
- hyalurinonidase - disrupts tissue connectivity
- exotoxins
- eyrogenic toxin
- DNases
