Atividade in vitro de agentes antimicrobianos contra biofilmes de Staphylococcus ssp. de otite canina

Abstract

Historically, bacteria have been seen as isolated organisms; however, it is now clear that the vast majority of bacteria exist in complex communities known as biofilms. Bacteria in biofilms are adhered to various surfaces, both abiotic and biotic (teeth, bones, mucosa), often forming a highly dynamic ecosystem, which is structured and organized. An example of infection, which can involve the formation of biofilm is otitis - defined as an acute or chronic inflammation of the ear, which may extend from the external ear canal to the inner ear. Described as the most common disease of the external ear canal in dogs, it has a multifactorial etiology, including fungi and bacteria, especially of the genus Staphylococcus. Bacteria of this genus are commensal to skin and mucous membranes, but can act as opportunistic pathogens in favorable conditions and are often associated with a wide variety of infections in humans and animals with many reports of refractoriness to usual treatments. In biofilm, bacteria can be ten to a hundred times more resistant to antibiotics when compared to the same bacteria in planktonic growth. The struggle to fight infections involving bacterial biofilms is a major challenge of microbiology today, which, in turn, leads to the search for new therapeutic options. Thus, this study aimed to evaluate the in vitro inhibitory effect of six substances – three classic antimicrobial agents ciprofloxacin, chloramphenicol, gentamicin; and three non-classic antimicrobial agents thymol, carvacrol, hydrogen peroxide (H2O2) - against staphylococcal strains from canine otitis in planktonic growth and in biofilm. We analyzed 54 clinical strains isolated from purulent secretion of canine otitis, divided into five species: S. intermedius, S. simulans, S. haemolyticus, S.epidermidis and S. lugdunensis. The 16 strains classified as biofilm producers (11 S. intermedius and five S. simulans), according to result obtained by the Congo red agar test and confirmed by scanning electron microscopy (SEM), were used in broth microdilution assay for determination of minimum inhibitory concentration (MIC) and minimum biofilm inhibitory concentration (MBIC). With regards to the biofilm-producing strains, the following results were observed: the values for ciprofloxacin were 0,12 ≤MIC≤0,5 mcg/mL (mean 0,28 mcg/mL) and 0,5≤MBIC≤8 mcg/mL (mean 1,79 mcg/mL); for chloramphenicol 2≤MIC≤16 mcg/mL (mean 7,41 mcg/mL) and 8≤MBIC≤32 mcg/mL (mean 20,71 mcg/mL); for gentamicin 0,5≤MIC≤4 mcg/mL (mean 2,09 mcg/mL) and 4≤MBIC≤64 mcg/mL (mean 24,24 mcg/mL); for thymol 32≤MIC≤512 mcg/mL (mean 137,41 mcg/mL) and 256≤MBIC≤2048 mcg/mL (mean 768 mcg/mL); carvacrol 32≤MIC≤512 mcg/mL (mean 128 mcg/mL) and 256≤MBIC≤4096 mcg/mL (mean 993,88 mcg/mL); and for H2O2 for 32≤MIC≤128 mcg/mL (mean 99,76 ppm) and 128≤MBIC≤4096 ppm (mean 1874,82 ppm). The presented data indicates the therapeutic potential of the six antibiotics studied in the treatment of staphylococcal infections associated with biofilm, which warrants further studies to investigate the mechanisms of action of these drugs on biofilms and the design of in vivo experiments to confirm the significance of these findings.