Derm 5 - bacteria Flashcards
how common is pyderma?
- Bacterial pyoderma is one of the most frequently encountered skin diseases in the dog. In fact, studies have shown that pyoderma is the second most common presenting dermatological complaint (the first is “not determined”!).
- Other than abscesses, it is a much less common reason for presentation in the cat.
types of pyoderma
- surface
- superficial
- deep
what characterizes a surface pyoderma?
Erythema, superficial exudation and erosions in the absence of pustules and epidermal collarettes
4 common types of surface pyoderma
- Intertrigo (fold dermatitis)
- pyotraumatic dermatitis
- mucocutaneous pyoderma
- bacterial overgrowth syndrome
BOG syndrome
(Bacterial OverGrowth)
- what is this? what does does it look like?
- lesions?
- underlying cause?
Bacterial hyperproliferation
No deep lesions noted
Marked pruritus
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Erythema
Lichenification
Hyperpigmentation
Malodorous greasy seborrhea
Excoriation
Alopecia
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2/3 are due to allergy
Superficial Bacterial Folliculitis (SBF)
- how common?
- signs/ lesions?
most common form of skin infection in the dog
Erythematous papules
Pustules
Epidermal collarettes
Crusts
Alopecia
Deep pyderma > types of lesions
- nodules
- ulcers
- draining tracts
recurrent pyoderma - common underlying etiology
- 67% of patients with recurrent pyoderma had
allergic dermatitis as an underlying etiology - Endocrine, cutaneous, metabolic or immunologic abnormality
- Immunodeficiency syndromes are really quite rare
why do dogs develop pyoderma?
Defective lipid barrier favours colonization and
multiplication of staphylococci = increased adherence
> Biofilm formation
> Bacterial overgrowth promotes adherence
> Quorum sensing: a switch is made from proliferation
to toxin production, leading to inflammation and
further reduction of skin barrier function
Reasons for treatment failure in the treatment of a papulopustular dermatitis
- Incomplete duration of treatment. The surface heals more rapidly than the deeper tissues. Discontinue treatment once lesions have resolved
- Overwhelming competitive factors. Recurrent or poorly responsive pyoderma could simply be a result of the inability of the antibiotics to keep the bacteria under control in the face of severe pruritus
- The lesion may not be bacterial in origin. Skin biopsies would be indicated
- Bacterial resistance
- inappropriate dose > consider minimum bactericidal conc / mutant prevention conc
- innappropriate choice of abx
- poor owner compliance
bacterial culture should be performed in cases where:
- There is less than 50% reduction in extent of lesions within 2 weeks of appropriate systemic antimicrobial therapy
- New lesions (papules, pustules, collarettes) are occurring in the face of treatment 2 weeks or more after the initiation of appropriate therapy
- Lesions persist and cocci are identified on cytology after 6 weeks of appropriate systemic antimicrobial therapy (while a typical course of therapy may be 21–28 days, several studies indicate that therapy for up to 6 weeks may be necessary to resolve the infection in some cases)
- Intracellular rod-shaped bacteria are present on cytology (rod susceptibility is difficult to predict)
- There is a prior history of multidrug-resistant infection in the dog or in a pet from the same household as the affected dog
- There is a history of recurrent infections or repetitive antibiotic use, even for unrelated disease (e.g., recurrent bladder infections?)
- when long-term treatment is likely to be needed
- poorly responsive cases > differentiate bacterial resistance from inability for antibiotics to overcome the pruritus
- Always???????
most common bacteria cultured from pyoderma
The most common organism cultured from bacterial pyoderma is Staphylococcus pseudintermedius.
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Most of the organisms formerly called Staphylococcus intermedius are more appropriately named S. pseudintermedius based on molecular phenotyping.
Methicillin resistant Staphylococcus (MRSP, MRSS)
- most common organsims cultured?
- what gene?
- resistance profile?
- MR staphylococcus pseudintermedius
- MR Staphylococcus schleiferi
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o They carry the mecA gene which alters the penicillin binding protein
> These organisms can be identified using MecA PCR or Penicillin Binding Protein 2a (PBP2a) latex
agglutination
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Resistant to ALL beta lactam antimicrobials but often multidrug resistant
when we send a sample to the lab, is it enough to know the genus? why?
no, we need species for resistance profile
> There are many coagulase negative organisms that are inherently methicillin resistant and yet of no clinical concern
Key Clinical Diagnostic Points in bacterial infections:
- what should we look for in recurrent cases?
- pruritus and pyoderma - which comes first?
- inexpensive tool that should regularly be performed.
- when to culture?
- how to culture deep infections
Always look for an underlying etiology in recurrent cases
Separate pruritic pyoderma from pyoderma leading to pruritus
Cytology is an inexpensive tool that should regularly be performed.
o All patients with rods on cytology should be cultured
All patients with non-responsive or recurrent pyoderma should be cultured
Cultures should be considered in patients that have been on multiple antibiotics, even for non-dermatological diseases
Deep infections should be cultured by biopsy: Studies have shown that surface culture predicted deep tissue isolates in only eight of 22 cases; “the majority of cases yielded positive growth of bacteria differing from superficial culture and often resistant to empirical drugs.”
