Bacteriology - skin infections Flashcards
What type of lesion does Staphylococcus pseudointermedius infection create?
Pustules; erythema, papules, collarettes
Function of Langerhan cells
Reside in epidermis (stratum spinosum / squamous cell layer) and take up/process antigens in skin infections => APCs
A part of the skin’s immune system // normal host defense mechanisms that prevent bacterial skin infections
What are the skin’s resident microflora and where do they reside?
Staphylococcus epidermis (coagulase negative)
- Reside in stratum corneum
- highest in moist, protected skin areas of the body (folds of skin, abdomen)
Opportunisitic
Surface Pyoderma
- inciting cause
- sterile or non-sterile site?
Staphylococcus pseduointermedius causes >90% of canine surface pyodermas
- Non-sterile site b/c within stratum corneum
S. pseudointermedius = coagulase+, transient flora
Superficial Pyoderma
- Two most common types
- sterile or non-sterile sites?
- Impetigo - puppy pyoderma
- Superficial Follculitis
Sub-corneal infections = Sterile site!
Describe the pathogenesis of Deep Pyodermas:
S. pseudointermedius +/- gram negatives (e.g., E. coli, Proteus spp., Pseudomonas aeruginosa)
- invade hair follicle -> infection spreads to the dermis, +/- subcutaneous tissue
Bacterial Furuculosis (draining tract), Acral Lick Dermatitis/Granuloma, Callous Pyoderms
Bumble Foot
- Inciting cause
- Pathogenesis
- Staphylococcus aureus = opportunistic pathogen (normal flora)
- BIRDS: poor perching -> trauma of foot -> S. aureus invades
Greasy Pig Disease
- Inciting cause
- Pathogenesis
- Streptococcus hyicus ss hyicus = opportunisitc pathogen (normal flora)
- PIGS: damage/trauma to skin -> S. hyicus ss hyicus invades
Diamond Skin Disease
- Inciting cause
- Pathogenesis
- Erysipelothrix rhusiopathiae
- ingested via environmental contamination (mostly by carrier animals) -> myocardial disease, septic arthritis from septicemic spread -> raised, erythemic diamond-shaped lesions
Pustular Dermatitis
- Inciting cause
- Signalment
- Streptococci spp.
- Nursing piglets
Dermatophilosis
- Inciting cause
- Pathogenesis
- Dermatophilus congolensis
- CATTLE & HORSES!
- prolonged wetting of skin by rain creates the ideal moist environment for the bacteria, which is spread by direct contact with carrier animals and/or fomites
Contagious Foot Rot (Sheep)
- Inciting cause
- Pathogenesis
- Dichelobacter nodosus and Fuseobacterium necrophorum
- warm/wet environment -> normal flora/opportunisitc F. necrophorum causes initial interdigital dermatits -> pathogenic D. nodosus attaches (via pili) & release protease
Mycobacteria
- habitat
- how are these bacilli organisms gram(+), yet stain gram(-)?
- differential stain to determine?
- VFs and pathogenesis?
- habitat = obligate parasites (permanent host) OR are saprophytic (environment // decaying vegetation)
- Gram positive: catalase (+)
- Stain gram negative b/c they have a lipid-rich cell wall => Acid-fast stain for differentiation!
- VFs: = Cord Factor (inhibit chemotaxis of neuts, leukocytes) and can survive/replicate in tissue MØ => granulomatous inflammation
Mycobacterial infections
Canine Leproid Granuloma Syndrome
- transmission
- canine signalment
- clinical signs
- tx
- transmission = mycobacteria transmitted via biting insects
- canine signalment = short-coated breeds (boxers)
- clinical signs = absence of systemic signs; non-pruritic and non-panful nodules (usually on head) that may ulcerate if large enough
- tx = self-limiting/curable condition :)
Mycobacterial infections
Feline Lepropsy Syndrome
- pathogenesis
- lesions
- pathogenesis = mycobacteria transmitted through wounds
- lesions = granulomatous cutaneous or SQ nodules (usually head / limbs) that may ulcerate
Mycobacterial Infections
Feline / Canine Panniculitis Syndrome
- pathogenesis
- dx technique
- tx
- Pathogenesis = trauma to skin (e.g., cat fight) -> dirt w/ mycobacteria contaminates the wound -> the mycobacteria grow rapidly in fatty tissues (inguinal area!!)
- Dx = FNA + cytology of nodules (NEVER from a draining tract!)
- Tx = Surgery!
“Panniculitis” = inflammation of subcutaneous fat
Staphylococcal infections
How would you sample and treat a surface pyoderma versus superficial pyoderma?
Surface Pyoderma - NONSTERILE site
- direct impression smears; sticky tape, swab -> looking for NON normal flora organisms (transient bacteria like Staph pseudointermedius) that can cause surface pyodermas
Superficial Pyoderma - STERILE site
- presumptive dx and treat empirically -> C&S if non-responsive to therapy from an *intact pustule
Superficial pyodermas typically respond WELL to empirical tx :)
Staphylococcal infections
How to collect a sample of a deep pyoderma?
Punch biopsy! (need to enter the deep dermis layer!)
- NEVER FROM A DRAINING TRACT!
Staphylococcal infections
Why is Culture +/- Susceptibility Testing contraindicated for surface and superficial pyodermas?
- Surface: susceptibility tests are based on drug concentrations reached in the serum and NOT on the surface (topical antimicrobials)
- Superficial: b/c these pyodermas typically respond well to empirical treatment
Staphylococcal infections
Why can pyodermal infections caused by Staphylococcus pseduointermedius be difficult to treat?
Staphylococcus pseudointermedius:
1. facultative intracellular parasites (won’t be killed by hydrophilic abx like cephalosporins)
2. increasing antimicrobial resistance (methicillin-resistance)
3. biofilm production (overcome action of ABXs)
S. pseudointermedius = transient organism of skin’s flora; coagulase+
Methicillin (INN, BAN) or methicillin (USAN) is a narrow spectrum beta-lactam antibiotic of the penicillin class.A
