Bacterial Pathogens of the Skin Flashcards
describe morphology and staining characteristics of mycobacterium spp. (5)
- hydrophobic outer layer rich in mycolic acid
-protects against host killing and interferes with gram stain reaction (retains dye (carbol fushion) despite acid decolorizing wash)
-acid-fast (ziehl-neelsen) staining used to aid diagnosis - rod-shaped (bacilli), 3 groups
-mycobacterium-tuberculosis complex (MTBC) mycobacteria
-non-tuberculous mycobacteria (NTM)
-fastidious mycobacteria - MTBC species are slow growing, cause disease in immune competent hosts, survive poorly outside of host reservoir, and are facultative intracellular pathogens of macrophages
-all MTBC species cause clinical tuberculosis (TB)
-ZOONOTIC potential!!
-10 species, including M. bovis, M. tuberculosis, etc. - NTM are opportunistic environmental saprophytes
-some slow grow like M. avium complex
-some rapidly growing like M. abscessus, M. smegmatis, M. fortuitum - fastidious mycobacteria (lepramatous) are difficult or impossible to culture using standard means
describe transmission of mycobacterium spp.
- inhalation of M. tuberculosis or M. bovis-containing respiratory droplets
-if you see an animal with M. tuberculosis, there IS A HUMAN somewhere in their life who also has M. tuberculosis (it is a human pathogen!!) - ingestion of raw milk or meat from infected cattle
-M. bovis - ingestion of M. avium complex in water and feedstuffs
- contamination of wound with environmental mycobacteria (MAC and RGM)
-common route in cats, less common route in dogs - ingestion or bite of M. microti-infected vole/mouse
-seen in cats and dogs in Europe
describe host granuloma formation as relates to mycobacterium spp.
- granuloma formation, also called granulomatous/pyogranulomatous host response is characteristic of this bacterium
-granuloma formation functions to contain bacterial spread - lesions due to intracellular and extracellular growth of the bacterium AND host responses
describe cutaneous disease associated with mycobacterium spp.
- more common in cats than dogs
-outdoor lifestyle
-contamination of wound by bacteria in environment - suspect in animals with chronic granulomatous/pyogranulomatous skin lesions unresponsive to antibiotics, especially in immunosuppressed animals
- MTBC causes nodular lesions +/- draining tracts in outdoor cats in EUROPE, NOT the US
- slow-growing NTB MAC organisms can cause ulcerated nodular lesions +/- draining tract +/- local LN enlargement
-may disseminate
-FIV/immunosuppressive drugs may predispose - suspect RGM in cats with chronic, draining, nodular/ulcerated lesions with SQ tissue involvement in inguinal area (panniculitis)
- fastidious mycobacteria (M. lepraemurium and others) can’t be cultured
-can cause single or multiple subcutaneous nodules of feline leprosy
describe diagnosis and treatment of mycobacterium spp.
diagnosis:
1. aspirate or biopsy of lesions
2. ID of acid-fast bacteria
-ALWAYS perform acid fast/ziehl-neelson staining if cytology/histology shows granuloma or granulomatous or pyogranulomatous inflammation
3. PCR/culture of biopsy tissue is definitive diagnosis because staining and culture so difficult
treatment:
1. months long
2. 2-3 drug combo therapy: fluroquinolone +macrolide (azithromycin or clarithromycin) + rifampin
3. REPORTABLE if MTBC organism but zoonotic risk of cutaneous lesions is low
describe morphology and staining characteristics of nocardia spp.
- gram positive, filamentous rods
- widely distributed in the soil and water
-NOT considered normal flora of animals
-opportunistic disease that causes pyogranulomatous inflammation - nocardia asteroides complex: includes many species of veterinary significance (often don’t determine the species)
describe transmission of nocardia spp.
- most often by contamination of wounds
- rarely by inhalation or ingestion
describe clinical disease caused by nocardia spp.
- disease may reflect underlying immunosuppression
- 3 disease forms
-localized skin form
-thoracic form: pneumonia, pleuritis
-septicemic/generalized form
-all 3 forms occur in dogs and cats - localized SQ lesions (mycetoma) with or without lymph node enlargement
-infection begins as a pustule or nodule that ruptures
-draining tracts form
describe diagnosis and treatment of nocardia spp.
diagnosis:
1. cytological prep of tissue biopsy with gram stain of lesion shows gram positive branching filamentous rods
2. culture/PCR confirmative
treatment:
1. surgical debridement with systemic antibiotics
2. treatment of thoracic and systemic forms often unrewarding
describe morphology and staining characteristics of dermatophilus congolensis
- gram positive, filamentous, branching
-hyphal form divides longitudinally and then transversely to form parallel rows of motile, coccoid organisms called zoospores (railroad trad appearance) - replicates only on animals
-carrier animals are primary source of infection
describe transmission of D. congolensis
- carriers maintain organism in population!
- transmission routes:
-direct contact with affected animals
-by contaminated fomites (grooming equipment, blankets)
-mechanically by flies - can survive for up to 3 years in crusts in the environment
- prolonged rainfall!!!, high humidity, higher temps, and trauma to skin favor transmission
-can see epidemics during rainy seasons
describe D. congolensis pathogenesis
- soaking or trauma to skin favors germination of motile coccoid zoospores what form hyphal-like branches in epithelium and invade hair follicles
- neutrophilic inflammation occurs and scab-like crusts develops
- organisms eliminated as epithelium regenerates and crusts are shed
-scabs are easily lifted by grasping hair
describe clinical disease of D. congolensis
- called dermatophilosis
-in horses: rain scald
-in sheep: lumpy wool
-affects cattle, horses, sheep, and goats
-rare in pigs, dogs, cats, and humans - causes purulent crusts and matted hair
- more common in animals exposed to chronic moisture, and in young and immunosuppressed hosts
- removal of crusts reveal a moist, gray to pink surface with hair roots protruding through the undersurface of crust
describe diagnosis and treatment of D. congolensis
diagnosis:
1. most often by clinical signs
2. stained, cytological prep of crusts for characteristic bacterial morphology
treatment/control:
1. remove crusts by grooming
-do NOT discard crusts into animals’ environment
-wear gloves due to ZOONOTIC potential
- topical chlorhexidine-based shampoo +/- systemic antibiotics
- control:
-shelter for prolonged rain exposure is most important
-fly control may also help
describe morphology and staining characteristics of erysipelothrix spp.
- gram positive rod (sometimes filamentous)
-primary pathogen is E. rhusiopathiae (a pathogen of swine and humans (erysipeloid)) - widespread in nature
-can survive for long periods in water and soil
-normal flora on skin of FISH
-also found on MM and in GIT of carrier swine
describe E. rhusiopathiae transmission
- mostly by ingestion of contaminated material: food, soil, water, feces
- found on skin of fresh and saltwater fish
-may be transmitted by ingestion of fishmeal (dietary supplement) - carrier pigs shed organism in nasal secretions, saliva, and feces
-infection can be acquired by direct contact with carriers, infected pigs, and fomites
describe erysipelas, the swine clinical disease of E. rhusiopathiae
- younger animals (3-18months) are most susceptible
- also called diamond skin disease
-reddish purple rhomboid-shaped skin infarct: thrombus with associated loss of blood supply, leading to tissue death (scab, necrosis) - can develop acute septicemia!!, endocarditis, arthritis
-can see one or any combo of symptoms
describe diagnosis, treatment, and control of E. rhusiopathiae
diagnosis:
1. blood culture
2. culture/PCR of tissues taken at necropsy confirms septicemia
treatment:
1. antibiotics: penicillin effective in outbreak
2. treatment not effective in chronic forms (arthritis)
control:
1. vaccines available (live-attenuated strains or formalin-fixed killed vaccines) to protect pigs
2. humoral/antibody immunity is protective
describe erysipeloid
- zoonotic disease in humans!
- enters via broken skin
- usually localized erythematous swelling at entry site (hands and fingers most common)
- occasional systemic complications observed
- penicillin treatment usually resolves infection
describe morphology and staining characteristics of staphylococcus spp.
- resides on skin and mucosal surface of ALL animals and people
- invade upon epithelial damage
-opportunistic - disease characterized by neutrophilic inflammatory response (pus)
- many make beta-lactamase
- S. hyicus causes disease in swine
describe S. hyicus transmission
- organism seeds skin during birth or transfers from skin of sow
- CANNOT penetrate intact skin!
-enters following injuries: lacerations, abrasions, caused by fighting or rough concrete floors or mites - virulent strains produce exfoliative toxin, which damages adhesions between keratinocytes
describe clinical disease of S. hyicus/greasy pig disease
- contagious exudative dermatitis in 1-8 week old pigs
- vesicles and pustules (esp around head) develop and rupture
- body covered in moist, greasy exudate (serum/pus), becomes crusty and contaminated with dirt
- disease probably systemic due to toxin absorption, resulting in degenerative changes in renal tubular epithelium
describe diagnosis, treatment, and prevention of S, hyicus
diagnosis: clinical signs and culture
treatment:
1. abx: susceptibiltiy testing is important!
2. skin wash: dilute chlorhexidine spray
3. oral electrolytes
prevention:
1. minimize fighting by maintaining stable pig groups
2. clip needle teeth before 3 days old to reduce biting damage
3. clean pens and provide soft bedding
describe morphology and staining characteristics of corynebacterium spp.
- small gram positive pleomorphic rods or coccobacillis
-genetically related to mycobacterium, nocardia, and rhodococcus - facultative intracellular bacteria of macrophages
-many species; few are pathogenic, some are normal flora
