BACTERIAL INFECTIONS OF

SKIN

Ishtiaq ahmed

• Portal of entry for bacteria into skin include

1. Pore (follicular openings)

2. Hematogenous spread

3. Direct entry through damages skin

Cutaneous bacterial infections vary in

1. Location (Epidermis, dermis, sub cut, adnexa or systemic)

2. Morphology (Pyogenic, granulomatous, necrotizing)

3. Distribution (focal, multifocal, regional, systemic, interdigital)

4. Severity (Mild, asymptomatic to sever with systemic signs)

Variation is due to specific organism involved, host-immune

response, predisposing/co-existing factors

• Involve epidermis & upper infundibulum of hair follicles

• Usually heal without scaring

• Etiology: Staphylococcus spp

• Gross lesions include erythema, alopecia, papules,

pustules, crusts and peripheral expanding rings of scale

called “ epidermal collarettes”

• Microscopically intra-epidermal pustuler dermatitis which

may rupture leading to formation of crust and scales

• Superficial luminal suppurative folliculitis

• Follicular injury leads to alopecia

• Impetigo is a superficial pustular dermatitis that does not

involve hair follicles

• Observed in dogs, cats, cow, does, ewes, piglets

• Caused by Coagulase + Staphylococci (S. intermedius)

• Cutaneous abrasions, viral infections, increased moisture

predispose for infection

• Protein A produced by bacteria binds to Fc part of IgG

leading to activation of complement system

• Chemo -attractants for leukocytes are produced leading to

inflammation and tissue damage

• Older dogs with hyperadrenocorticism induced

immunosuppression may develop bullous impetigo

• Cows, does, ewes have usually lesions on udder

• Kittens: shoulders and neck due to overzealous mouthing

of the queen.

• Streptococcus and Pasteurella are cause

• Grossly pustules, crusts in non haired skin except kitten

• Non follicular neutrophillic subcorneal pustule

Impetigo in dog

Subcorneal pustule

Superficial spreading pyoderma

• Common bacterial infection in dog, often pruritic

• St. intermedius

• Pathogenesis poorly understood

• May be bacterial hypersensitivity as IgE agianst

Staphylococcus has been detected

• Protein A may also contribute

• Lesions mostly on ventral thoracic and abdominal skin,

dorsal and lateral trunk as well

• Erythematous macules, papules, transient pustules

• Older lesion: epidermal collarettes, alopecia, crusts,

hyperpigmentation

• Superficial spongiotic pustules ….crust….basophilic

debris

• Dermal lesions inculde superficial perivascular or

interstitial accumulation of neutrophils, eosinophils,

macrophages

Mucocutaneous pyoderma

• Putative bacterial infection of muco-cutaneous junction in

dog

• German Shepherd

• Erythema, depigmentation, crusting, ulceration

• Histologically: Lymphoplasmacytic infiltration at

epidermal-dermal junction (lichenoid)

• No basal cell degeneration

• Spongiosis, cellular exocytosis, neutrophillic pustular

crust, folliculitis

Dermatophilosis

• cutaneous streptothricosis, mycotic dermatitis,

cutaneous actinomycosis, lumpy wool, strawberry foot rot,

rain scald, rain rot, Kirchi, Gasin-Gishu, Senkobo disease,

Drodo-Boka, Savi, Ambarr-Madow

• Acute, subacute, or chronic superficial exudative

dermatitis caused by the actinomycete Dermatophilus

congolensis

• Worldwide occurrence, wide host range

• Hot humid tropics and subtropics and in areas with

prolonged rain

• In hot monsoon cattle usually affected

• In temperate climates sheep, goat primarily affected

• Lesions tend to develop on dorsum of back and distal

extremities

• Ectoparasites, trauma, wetting of skin allow zoospores to

enter in epidermis

• Bacterium grow in outer rootsheath of hair follicle

• Produces gram positive filamentous branches

• Induce acute inflammatory response

• Intraepidermal microabcess

• Repeated bacterial growth cycles and inflammation lead

to multilaminated pustular crusts

• Papule, pustule, crust that can mat the hairs/wool

• Hyperplastic superficial perivascular dermatitis

• Multilaminated crusts of alternating layers of keratin and

neutrophils covering the skin

Exudative Epidermatis pigs

• Greasy pig disease

• Staphylococcus hyicus

• In neonatal pigs fatal, mild in old pigs

• Bacteria produces exotoxin “ exfoliatin”

• Exfoliatin binds to filaggrin in the keratohyalin granuels in

st. granulosum

• It causes focal erosion of epidermis

• Dermatitis and brown exudate develop around the eyes,

pinnae, snout, chin, medial legs, spread to ventral thorax

& abdomen

• It gives animal an over all greasy appearance

• Lesions rapidly coalesce to become generalized

• Malodourous exudate cover skin

• If animal survive, exudate hardens, cracks and form

fissures

• Sub acute disease in older pigs with lesions face, pinnae

and perioccular lesions (Epidermal thickness and scaling)

• Histopathology:

• Subcorneal pustular dermatitis

• Superficial suppurative folliculitis

Ovine fleece rot

• Superficial dermatitis

• Excessive moisture due to rain cause proliferation of

Pseudmonas spp

• Approximately 1week wetting required

• Acute inflammatory response with serum exudation and

fleece mating

• Fleece discolored because of chromogens produces by

bacteria and has rotten odour

• Epidermal pustular dermatitis and folliculitis

• Secondary Myasis

Deep bacterial pyodermas

• Bacterial infections of hair follicles, dermis and sub cutis

• Staphylococcus, streptococcus, corynebacterium,

pseudotuberculosis, pseudomonas, Proteus, E.coli,

pasturella

• Staphylococcus intermedius is primary pathogen of

canine skin

• Immunosupperssion and demodicosis are predisposing

factors

Staphylococcal folliculitis & furunculosis

• Folliculitis may be superficial or deep

• Superficial involve infundibulum, it can spread deeper

• Severe folliculitis can result in frunculosis

• Most common in dog. Horse, sheep, goat may also

develop disease

• In dog lesions on dorsal nose, pressure points, interdigital

areas

• Deep pyoderma in German Shepherd with genetic

predispostion

• In horses lesions develop under the saddle, tail, pastern

• Pastern or fetlock (equine pastern folliculitis)

• In goats, face, pinnae, udder, ventral abdomen, medial

thigh, perineum

• Grossly: initially papules, crusted papules, pustules,

collarettes, alopecia

• Deep lesions have hemorrhagic bullae, nodules, draining

tracts

• Microscopically: luminal folliculitis, pyogranulomatous

furunculosis , draining sinuses and occasionally

panniculitis

•

Subcutaneous abscess

• Localized collection of purulent exudate in dermis and sub cutis

• Common in cats because of contamination of puncture wounds

• Also common in large animals

• Foreign bodies, shearing and clipping wounds, injections

• Granulation tissue or fibrous tissue surrounds the exudate

• Abscess drain and heal with scarring

• Commonly isolated bacteria Pasteurella multocida (dog, cat

bite wounds), Corynebacterium pseudotuberculosis (horse,

sheep, goat), Arcanobacterium pyogenes (sheep, goat, cattle,

pig)

• Other bacteria include b-hemolytic streptococci, staphylococci,

fusobacterium, bacteroids, clostridium

Bacterial Granulomatous dermatitis

• Usually due to traumatic implantation of bacteria

• Mostly saprophytes of low virulence

• Initiate strong cell mediated immune response

• Grossly lesion can be slow progressing, nodular or diffuse

• Mixed cellular population , chiefly macrophages

• Granulomas, giant cells, caseous necrosis

Mycobacterial granulomas

• Mycobacteria produce granulomatous to

pyogranulomatous dermatitis in skin especially in cats

• Intracellular bacteria

• Survive and multiply by preventing formation of

phagolysosome

• Tissue destruction with persistence of antigen and CMI

response

• Obligate (M. bovis, M. tuberculosis, M. lepraemurium) or

saprophytic bacteria(M. fortuitum, M. smegmatis etc),

opportunistic (M. avium-intracellular complex)

• Infection via wound contamination or traumatic

implantation

• Infection with M. bovis & M. tuberculosis is referred as

tuberculosis

• Infection with other is called mycobacteriosis (atypical,

avian etc)

Mycobacterial infection is more common with rapidly

multiplying opportunistic organism

More common in cat

Lesions are recurrent nodules with draining sinuses in the

inguinal areas

• Organisms mostly found in extracellular space line by neutrophils

• In cattle skin lesions caused by opportunistic mycobacteria historically called skin tuberculosis occur as single or multiple nodules (1-8 cm ) in dermis and sub cutis especially in lower legs.

• Lesions may spread via lymphatic to other regions

• Udder skin is sometimes involved

• Causative agent is mostly saprophytic atypical mycobacteria e.g. M. kansasii

• Firm (pyogranulomas with fibrosis & mineralization) or fluctuating nodules (thick wall abcess) connected by thin cords of tissue

• False positive reaction for tuberculosis

Atypical mycobateriosis, pyogranuloma

cat

• Feline leprosy caused by M. lepraemurium is common in cats in cold areas of the world

• Biting of cats or rodents, insect vectors, soil contamination of wounds

• Lesion develop on head, neck and limbs

• Does not grow in culture with routine techniques

• PCR used for identification

• M. visibile also identified in skin lesions

• Two histological pattern of lesion

• One with diffuse granulomatous without necrosis and large number of acid fast bacilli

• Other central necrosis surrounded by lymphocytes

•

• Cutaneous infection with M. bovis & M. tuberculosis are

rare

• Mycobacteria in macrophages ZN staining

Botryomycosis

• Granulomatous dermatitis caused by non-filamentous bacteria typically staphylococcus spp, streptococcus, pseudomonas aeruginosa, proteus, actinobacilluslignierisii

• These bacteria form small yellow “ sulfur” containing granules with centrally located bacterial colonies surrounded by radiating club shaped eosinophilic bodies called splendore hoeppli material.

• The material is considered antigen antibody material

• Lesions are progressive nodular lesions in cutaneous or subcutaneous areas

• Differential: Actinomycotic mycetomas, Eumycoticmycetomas (fungi)

• Filamentous bacteria also cause granulomatous

dermatitis

• Nocardia, Actinomyces

• Differentiated from botryomycosis by gram stain and

culture

• Granulomas contain mycelial filaments upto 1 cm

• Progressive nodular lesions can involve underlying bones

• E.g. lumpy jaw

• Source: Jubb kennedy and palmer’s Pathology of

domestic animals