skin microbiology 1+2 Flashcards
explain why different locations on the body will have different microbiology
- secretions vary by site
- immune cell distribution varies in layers
- local humidity varies
- mucosa vs keratinocyte
- local environments have an impact on microbiology
explain how skin is a barrier and defended environment against microorganisms
- barrier = keratinised cells
- turnover of cells sheds potential resident organisms (unless top layer is punctured)
- environment is dry and has specific ph
- lipids and antimicrobial peptides and immunoglobulins secreted
- immune cells within the skin (neutrophils, macrophages, intraepithelial lymphocytes and NK cells
what type of cell is indicative of bacterial infection
neutrophils
what type of cell is indicative of deeper skin infection
macrophages as they live in lower layers of skin
what are resident pathogens
commensals
can replicate on the skin and can persist
what is an opportunistic pathogens
organism that would normally be commensal but in position or condition it can cause disease
what is a nomad pathogen
organism that can colonise and reproduce on the skin for short times
what is a transient pathogen
cannot replicate so stay for a short period of time but can grow out of control if imbalance
what are pathogens
organisms that become established and can proliferate on the skin surface and deeper that are deterious to normal physiology of the skin
what does dysbiosis mean
changes from balanced (normal) to unbalanced microflora
what factors increase risk for infection
- moisture/humidity
- damage
- normal tissue maintenance
- washing (overwashing esp)
- behaviour
- health
- physical breaches to the barrier
- veterinary interventions
describe staphylococcal bacteria and its pathogenicity
- gram positive, facultative anaerobes. coccoid and often seen in clusters but sometimes in small groups and pairs
- commensals but often occur as opportunistic pathogen
- confim via Mass spec, PCR or serology
- infection can cause pyogenic lesions (neutrophil related) leading to pus and can form abscesses OR granulomatous inflammation (macrophage related) or combo (pyogranulomatous)
- minor trauma damage may predispose to disease and they can possess a number of virulence factors (coagulase, lipases, protein A inhibits opsonisation, toxins)
name clincially important staphylococcus species
- S hyicus (a species whose procine subspecies are opportunistic pathogens associated with epidermal infection in pig (greasy pig disease))
- S. pseudointermedius (commensal and can infect the skin of domestic dogs and cats)
- S. Aureus (derm infections of a number of animals and one of the possible causes of mastitis in cattle)
desribe pseudomonas and its pathogenicity
- gram neg rods, aeroibic, motile
- common in the environment and are both pathogenic and non-pathogenic strains
- colonies tend to be slimy due to a biofilm (polysaccharide mucous secreted by them)
- non spore forming but hardy. biofilms help make them refractive to treatment
describe proteus mirabilis and its pathogenicity
- gram negative rods, facultative anaerobes
- motile, swarm can be observed on plates and have characteristic fishy smell
- can cause ear infections but also associated with UTIs (likely due to fecal contamination as is an enteric commensal)
describe dermatophilosis and its pathogenicity
- gram positive filamentous bacterium, actinomyecete
- motile zoospore stage is activated to form a mycelium. the zoospores can remain dormant in skin debris and scabs for many months in dry conditions
- associated with heavy prolonged rainfall or skin damage.
- initial infection requires at least superficial skin damage
- confined to the epidermis
- more prevalent in younger animals
- lesions are papules early on followed by serous exudative dermatitis with scab formation
- (mud fever)
list general factors critical to establishment of infection
- exposure (esp ringworm)
- critical mass of infective material (or critical time)
- grooming effectively to remove material
- spores require warm humid conditions to infect
- pre-existing conditions
- immune status
list contributing factors for oppotunistic malassezia infection
- hypersensitivity disorders
- keratinisation defects
- hot, humid weather
what species have higher levels of malassezia than other breeds
- bassets
- dachshunds
- cocker spaniels
- west highland white terriers
describe dermatophytosis infections
- grow exclusively in the non-living tissue of skin, nails and hair
- secrete enzymes and absorb nutrition from tissues
- septate, filamentous fungi
- reproduce both sexually and asexually
- grow aerobically at 25 degrees (outside body)
- slow growing (antibac materials needed in culture plates)
ringworm
how long is the incubation period of ringworm
1 week
what type of hair does ringworm invade in cattle
anagen hairs
why is alopecia a common symptom of ringworm
hair breaks off due to weakening as the pathogen digests keratin
what class of dermatophyte is most commonly seen in cattle
Trichophyton verrucosum
why is youngstock commonly affected by ringworm infections
less resistant
what is the most common dermatophyte species seen in horses
trichophyton equinum
