skin microbiology 1+2

Question 1

explain why different locations on the body will have different microbiology

Answer 1

• secretions vary by site
• immune cell distribution varies in layers
• local humidity varies
• mucosa vs keratinocyte
• local environments have an impact on microbiology

Question 2

explain how skin is a barrier and defended environment against microorganisms

Answer 2

• 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

Question 3

what type of cell is indicative of bacterial infection

Answer 3

neutrophils

Question 4

what type of cell is indicative of deeper skin infection

Answer 4

macrophages as they live in lower layers of skin

Question 5

explain how staphylococcal super antigen causes hypersesnitivity

Answer 5

• superantigens over activate T-lymphocytes by

Question 6

what are resident pathogens

Answer 6

commensals
can replicate on the skin and can persist

Question 7

what is an opportunistic pathogens

Answer 7

organism that would normally be commensal but in position or condition it can cause disease

Question 8

what is a nomad pathogen

Answer 8

organism that can colonise and reproduce on the skin for short times

Question 9

what is a transient pathogen

Answer 9

cannot replicate so stay for a short period of time but can grow out of control if imbalance

Question 10

what are pathogens

Answer 10

organisms that become established and can proliferate on the skin surface and deeper that are deterious to normal physiology of the skin

Question 11

what does dysbiosis mean

Answer 11

changes from balanced (normal) to unbalanced microflora

Question 12

what factors increase risk for infection

Answer 12

• moisture/humidity
• damage
• normal tissue maintenance
• washing (overwashing esp)
• behaviour
• health
• physical breaches to the barrier
• veterinary interventions

Question 13

describe staphylococcal bacteria and its pathogenicity

Answer 13

• 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)

Question 14

name clincially important staphylococcus species

Answer 14

• 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)

Question 15

desribe pseudomonas and its pathogenicity

Answer 15

• 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

Question 16

describe proteus mirabilis and its pathogenicity

Answer 16

• 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)

Question 17

describe dermatophilosis and its pathogenicity

Answer 17

• 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)

Question 18

list general factors critical to establishment of infection

Answer 18

• 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

Question 19

list contributing factors for oppotunistic malassezia infection

Answer 19

• hypersensitivity disorders
• keratinisation defects
• hot, humid weather

Question 20

what species have higher levels of malassezia than other breeds

Answer 20

• bassets
• dachshunds
• cocker spaniels
• west highland white terriers

Question 21

describe dermatophytosis infections

Answer 21

• 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

Question 22

how long is the incubation period of ringworm

Answer 22

1 week

Question 24

what type of hair does ringworm invade in cattle

Answer 24

anagen hairs

Question 25

why is alopecia a common symptom of ringworm

Answer 25

hair breaks off due to weakening as the pathogen digests keratin

Question 26

what class of dermatophyte is most commonly seen in cattle

Answer 26

Trichophyton verrucosum

Question 27

why is youngstock commonly affected by ringworm infections

Answer 27

less resistant

Question 28

what is the most common dermatophyte species seen in horses

Answer 28

trichophyton equinum