Chapter 4 - Bacteria Flashcards
What is the most common metabolic cause of skin infection in horses?
Pituitary pars intermdia dysfunction
Are the below antibiotics bacteriostatic or bactericidal? TMPS Macrolides FQs Gentamicin Tetracyclines
TMPS - bactericidal Macrolides - bacteriostatic FQs - bactericidal Gentamicin - bactericidal Tetracyclines - bacteriostatic
Macrolides concentrate in phagocytic cells; true or false?
True
Why should chloramphenicol not be given to animals in the food chain?
It causes a severe, idiosyncratic bone marrow dyscrasia in people
Name two Staphylococcal superantigens that can trigger local cutaneous and immunological responses
Protein A
Enterotoxin C
Name two Strep equi equi virulence factors
- A hyaluronic acid capsule
- M(SeM) protein which inhibits phagocytosis and complement deposition and bactericidal mechanisms of neutrophils and macrophages (can test for antibody titres)
Corynebacterium spp. are gram-positive, pleomorpohic bacteria, true or false?
True
Which virulence factor of Corynebacterium pseudotuberculosis can:
Hydrolyse lysophosphatidylcholine and sphingomyelin, degrading endothelium and increasing vascular permeability (oedema) AND inhibit neutrophil chemotaxis and degranulation of phagocytic cells.
Phospholipase D
Which insect vector is through to be involved in the development of Corynebacterium pseudotuberculosis abscesse in horses?
Biting flies, especially horn flies (Haematobia irritans).
Stomoxys calcitrans, and Musca domestica also likely
Does moisture or heat cause the release of infective, motile, flagellated zoospores form of D. congolensis?
Moisture
D. congolensis possess an alkaline ceramidase gene; this catalyses the cleavage of ceramide to _____ and ______ in the epidermis.
Fatty acids and sphingosine
Why are white areas of skin affected with D. congolensis often associated with severe erythema?
They may represent a type of photodermatitis caused by D. congolensis.
Name three differentials for dermatophilosis
Dermatophytosis Staph. folliculitis Demodicosis PF Sterile eosinophilic folliculitides
Which histopath stains can be used to visualise D. congolensis?
Giemsa
Brown and Brenn
Acid orcein-Giemsa
Can be seen with H&E
When active lesions are not present, avulsed thick crusts can be used to demonstrate D. congolensis organisms on histopath or culture?
Histopath
Culture in chronic, non-exudative stages can be overgrown by secondary invaders and saprophytes
Do horses previously affected by dermatophilosis have lasting immunity to prevent reinfection?
No
Which special stains help demonstrate Actinomyces on histopathology?
Gram (+ve)
Grocott methenamine silver
Which systemic disease process should be considered in horses that develop bacterial pseudomycetoma?
Pituitary pars intermedia dysfunction
Most reported cases of clostridial infections in horses are associated with what?
IM injections
Which aerobic, gram-negative rod causes glanders?
Burkholderia mallei
Is Burkholderia mallei a zoonotic agent?
Yes - infection is usually fatal
Which systemic sign accompanies nodular skin lesions in glanders?
Mucopurulent nasal discharge
In the chronic form, nasal and subcutaneous nodules develop, eventually ulcerating. Lymph vessels are enlarged and nodular abscesses form along their course and discharge yellow pus.
What are the main cutaneous signs associated with purpura haemorrhagica?
S/C limb oedema
Haemorrhage on mucous membranes
Which Staph. most often causes folliculitis in horses?
S. aureus
Name three follicular causes of pustules/crust in horses
Staph. folliculitis
Demodicosis
Dermatophytosis
Name three non-follicular causes of pustules/crust in horses
Dermatophilosis
Mites (e.g. Chorioptes)
Allergic skin disease (e.g. IBH, contact)
PF
In the study by Kaiser‑Thom et al. (2022), were Staph. isolates higher in horses with pastern dermatitis compared to healthy controls?
Yes - from pastern (59.0 % vs. 6.3 % in unaffected horses; P<0.001), and nose (59.0 % vs. 8.4 %; P<0.001).
In horses with pastern dermatitis, how did Staph. populations differ from pastern and nasal swabs?
Antimicrobial resistance genes were almost equally frequent in pastern and in nasal samples, whereas some virulence factors such as the beta‑hemolysin, ESAT‑6 secretion system, and some enterotoxins were more abundant in isolates from pastern samples, possibly enhancing their pathogenic potential
Other than Staph. aureus, which other Staph. can be associated with pyoderma in horses?
Staphylococcus hyicus subsp. hyicus
Staphylococcus delphini
Which antisepetic shampoos/sprays can be used to treat Staph. infection in horses?
Chlorhexidine
Benzyl peroxide
Iodophors (e.g., povidone-iodine)
In the study by Van den Eede et al. (2012), what % of long-term hospitalised horses carried MRSP? Which body site was most frequently positive?
40%
Nostrils
How was bacterial diversity affected in horses with equine pastern dermatitis (affected limb compared to non-affected limb)?
Bacterial alpha diversity was reduced in affected pasterns (P<0.001) and this reduction was significantly associated with the EPD forms (P<0.001), and not with the type of pretreatment (P>0.14)
Name four differentials for Staphylococcal pastern folliculitis and furunculosis
- Other bacterial infection
- Dermatophilosis
- Spirochetes
- Dermatophytosis
- Chorioptic mange
- Trombiculiasis
- Pelodora
- Vaccinia
- Irritant contact dermatitis
- Allergic contact dermatitis
- Photosensitisation
- Trauma
- Vasculitis
- PF
- CPL
Name two toxins produced by CoPS
- Enterotoxins A, B, C, D (C = superantigen)
- Protein A (= superantigen)
- Haemolysins
- Leukocidins
- Dermonecrotoxins
Which haematological finding was associated with the development of purpura haemorrhagica in horses with Strep equi subsp. equi infection?
Anaemia
Are S. equi M protein (SeM) antibody titers elevated with complications?
No - SeM antibody titers can be increased after infection in the absence of complications of strangles
Cutaneous and internal abscesses and ulcerative lymphangitis are clinical features of Corynebacterium pseudotuberculosis infection in horses. Most commonly, abscesses develop in the ________, ________, _________, and _______ areas. Local wound care should be an integral part of treatment.
Pectoral, axillary, ventral abdominal and inguinal areas
Severe cellulitis, panniculitis, and skin sloughing of the head region has also been described
What treatment is indicated for Corynebacterium pseudotuberculosis infection in horses?
Drainage and systemic antibiotics are necessary to cure the lesions. The organism is typically sensitive to penicillin and oral sulfonamides
Occasionally, C. pseudotuberculosis infection can progress causing lymphangitis. Name other organisms than can cause ulcerative lymphangitis
Bacterial = Pseudomonas, Pasteurella and Actinomyces spp. Fungal = Histoplasma
True or false; Dermatophilus congolensisis a Gram-positive coccobacillary actinomycete that causes an exudative dermatitis in a variety of species, most notably in ruminants and horses, although rare infections occur in cats, dogs, and humans.
True
Which molecular test can be performed on crusts in suspected cases of dermatophilus congolensisis if cytology is negative?
RT-qPCR
What is the primary source of infection for dermatophilosis?
Chronically infected horses
What are mechanical vectors of dermatophilosis?
- Biting and non-biting flies
2. Contaminated clippers
The environment may be a source for recontamination with Dermatophilosis because the zoospores resist drying at 100ºC and can survive in dry scabs at 28–31ºC for ___ months
42
What are the primary lesions of dermatophilosis in horses?
Follicular and non-follicular papules and pustules
What are the four types of lesion distribution commonly seen with dermatophilosis in horses?
- Rump and topline (‘rain scald’)
- Saddle area (associated with tack)
- Face and neck (associated with tack)
- Pasterns, coronets and heels (‘grease heel’, ‘scratches’, ‘mud fever’ – associated with poorly drained/muddy pastures)
Which stains can be used to identify Dermatophilosus congolensis on cytology?
Diff Quik, Gram, methylene blue
How do you prepare a macerated crust slide for cytology?
- Place 1–2 drops of saline on a clean slide.
- Clip off excess hair from the crust sample and place crust into saline.
- Macerate/soften for 15 minutes then remove larger pieces.
- Crush remaining material on the slide and allow to air dry.
- Heat fix slide for a few seconds.
- Stain with Diff Quik or methylene blue and allow to dry.
How do you treat dermatophilosis in the horse?
- Keep the animal dry (may spontaneously regress in 4 weeks)
- Remove and dispose of crusts (may require sedation as painful)
- Topical treatment e.g. lime sulfur, iodophors or chlorhexidine
- Systemic antibiotics e.g. penicillins, TMPS, erythromycin
- Improve hygiene and management practices
What is in the circle in this image?
Dermatophilus congolensis
True or false; It is important to burn or properly dispose of crusts to prevent spread of dermatophilosis to other animals.
True
CoPS are isolated from what % of cases of equine cellulitis?
> 80%
Which breed of horse are most commonly reported with cellulitis?
Thoroughbreds
What are the clinical signs of ulcerative lymphangitis in the horse?
- Hindlimb fetlock most common site, rarely above hock
- Hard to fluctuant nodules/abscesses that ulcerate and develop draining tracts
- Corded regional lymphatics
- Oedema, cellulitis and fibrosis (particularly with C. pseudotuberculosis)
- Lameness, fever, anorexia
Rhodococcus equi rarely causes cutaneous abscesses, cellulitis and ulcerative lymphangitis in horses; what clinical signs are more common with this infection?
Pneumonia and lymphadenitis in foals
True or false; in dermatophilosis, intracellular oedema and reticular degeneration of keratinocytes is a striking feature on histopathology
True
Are most horses with Nocardia infection immunocompromised?
Yes
Actinobacillus equi causes which diseases in horses?
- ‘Shigellosis’ a fatal septicaemia in foals
- Bacterial pseudomycetoma
Skin biopsy from a granulomatous skin lesion; what is the arrow pointing at?
Eosinophilic tissue grain
Splendore-Hoeppli
What is the most commonly isolated bacteria from subcutaneous abscesses in the horse?
Corynebacterium pseudotuberculosis
Name two differential diagnoses for bacterial pseudomycetoma in horses
- Other bacterial and fungal granulomas
- Foreign body granuloma
- Habronemiasis
- Granulation tissue
- Neoplasia
What are the clinical signs of clostridial infection in horses?
- Warm, painful, pitting, deep swelling
- Serosanguinous, foul-smelling draining fluid
- Develops to cool, hypoesthetic, blue-purple skin
- Necrosis and sloughing
- Fever, depression, tachycardia
- Toxaemia and death can occur within a week
- Laminitis is a common complication
How do you treat clostridial infection in horses?
- IV potassium penicillin
- Surgical wound management (disrupt anaerobic environment)
- Analgesia (very painful!)
Which are the most common anaerobes involved in cellulitis, abscesses and draining tracts in horses?
Clostridium spp.
Bacteroides spp.
Fusobacterium spp.
Which special stain can be used to identify bacillus anthracis?
Gram
How long can Burkholderia mallei (glanders) survive outside the body?
3-5 weeks
What is the main differential diagnosis for Burkholderia mallei (glanders)?
Histoplasma farcinimosi (epizootic lymphangitis) - lymphangitis and respiratory disease
What is the mallein test?
Mallein, a heat-extracted protein from B. mallei, is injected intradermally into the lower eyelid and measured 24-48 hours later
PCR an alternative
Which strain of MRSA is commonly found in horses in Europe?
Clonal complex (CC)398
In rural Germany, what % of non-hospitalised horses carried MRSA and ESBL E. coli?
MRSA - 0.9%
ESBL E. coli - 4%; associated with prior antibiotic treatment and veterinary examinations
