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have markedly altered metabolism, enhanced cell-to-cell communication, and are able to evade the host immune response and the effects of antimicrobials through their isolated metabolism along with physical and chemical protection of the biofilm matrix.
Biofilm formation is influenced by a number of factors including:
treatment of a Pseudomonas otitis, the concentration of the medication should be increased. (Pye 2013)
N-acetyl cysteine (NAC) is a mucolytic with antibacterial and antioxidant properties. It is also otoprotective and can prevent chemotherapy induced hearing loss and contributes to detachment of biofilms associated with P.aeruginosa. Recently it has been demonstrated
that NAC has an inhibitory effect in vivo against
common pathogens isolated from canine otitis externa; S.pseudintermedius, Pseudomonas aeruginosa, Corynebacterium and haemolytic Streptococcus. The product appears to be safe and well tolerated and has an inhibitory effect at a concentration of 1%; middle ear mucosal inflammation was reported at concentrations > 2% and conductive hearing loss at 4%. (May 2016). NAC could be incorporated as part of the ear cleaning routine if a biofilm is suspected.
REFERENCES
Bradley CW, Morris DO, Rankin SC, Cain CL, Misic AM, Houser T, Mauldin EA, Grice EA. Longitudinal evaluation of the skin microbiome and association with microenvironment and treatment in canine atopic dermatitis. Journal of Investiga- tive Dermatology. 2016 Jun 1;136(6):1182-90.
de Jongh GJ, Zeeuwen PL, Kucharekova M, Pfundt R, van der Valk PG, Blokx W, Dogan A, Hiemstra PS, van de Kerkhof PC, Schalkwijk J. High expression levels of keratinocyte antimicrobial proteins in psoriasis compared with atopic dermati- tis. Journal of investigative dermatology. 2005 Dec 1;125(6):1163-73.
Hoffmann AR, Patterson AP, Diesel A, Lawhon SD, Ly HJ, Stephenson CE, Mansell J, Steiner JM, Dowd SE, Olivry T, Suchodolski JS. The skin microbiome in healthy and allergic dogs. PloS one. 2014 Jan 8;9(1):e83197.
May ER, Conklin KA, Bemis DA. Antibacterial effect of N-acetylcysteine on com- mon canine otitis externa isolates. Veterinary dermatology. 2016 Jun 1;27(3):188.
Pierezan F, Olivry T, Paps JS, Lawhon SD, Wu J, Steiner JM, Suchodolski JS, Rodrigues Hoffmann A. The skin microbiome in allergen-induced canine atopic dermatitis. Veterinary dermatology. 2016 Oct 1;27(5):332.
Pye CC, Yu AA, Weese JS. Evaluation of biofilm production by Pseudomonas aeruginosa from canine ears and the impact of biofilm on antimicrobial suscepti- bility in vitro. Veterinary dermatology. 2013 Aug 1;24(4):446.
· Bacterial species:
· Environmental conditions: temperature, pH,
oxygen concentration, iron availability · Surface: rough versus smooth
The stages of biofilm formation progress from initial attachment to the surface, through a phase of maturation, to a final phase of dispersion. Once the biofilm has formed, it confers a number of survival advantages
for the bacteria that can have significant effects on pathogenicity including:
· Creates a high density of bacteria
· Increased metabolic efficiency
· Evasion of host defences such as phagocytosis
· Exchange of genes resulting in more virulent strains
· Increased production of toxins
· Protection against microbial agents
· Provides a nidus of infection that permits detach-
ment allowing spread to other sites
How are they relevant?
Biofilms have a major impact on treatment and antimicrobial resistance, particularly in canine otitis externa. They are common and under-diagnosed, although they can be easily identified on otoscopy or cytology. Clinically, they form an adherent, thick and slimy discharge that is often dark brown or black in
both the external ear canal and middle ear cavity. On cytology they appear as variably thick veil-like material that may obscure bacteria and cells. Biofilms are clinically important as they inhibit cleaning, prevent penetration
of antimicrobials and provide a protected reservoir
of bacteria. Also, antimicrobials that require bacterial division will be less effective, as bacteria in biofilms are usually in a quiescent state. Biofilms may also enhance the development of antimicrobial resistance, especially in Gram-negative bacteria that acquire stepwise resistance mutations to concentration-dependent antimicrobials.
Biofilm production by canine otitis isolates of
P. aeruginosa is common and may play a role in
the pathogenesis of disease. The MICs for biofilm- embedded bacteria differ from their planktonic counterparts, potentially leading to a lack of response
to treatment. In one study, 40% of canine otic isolates
of P. aeruginosa were classified as biofilm producers. Biofilm MICs for polymyxin B, neomycin, gentamicin
and enrofloxacin were significantly higher than for the planktonic form. If these medications are used for topical
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