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Staphylococcus aureus is one of the most common pathogens that cause recurrent, chronic, and biofilm-related diseases. Biofilms are the major form of bacterial structures capable of secreting polysaccharides that provide intrinsic protection against environmental stress like high concentrations of antibiotics. This, along with the emergence of multidrug-resistant strains, has made S. aureus infections a worldwide problem as a result of the inefficiency of the conventional medications. Plant essential oils (EOs) are an important source for drug discovery and pharmaceutical development due to their diverse biological activities, such as antimicrobial agents. The EOs' microbicide action is extensively reported at the scientific literature and frequently associated with bioactive molecules, such as aldehydes and terpenes. However, the ability of some EOs to inhibit biofilm formation has been poorly explored and it is still unclear how they could be applied in specific treatments against well-known infections. Therefore, this chapter will address virulence factors and biofilm formation of S. aureus, as well as bioprospecting of essential oil as a promising source in the search for new bioactive compounds employed in the fight against this microorganism.

The aim of this study was to evaluate the phytochemical profile of Cinnamomum zeylanicum essential oil (CZEO) and their antimicrobial and antibiofilm activity against Staphylococcus strains isolated from canine otitis. First, the CZEO chemical composition was determined by gas chromatography-mass spectrometry (CG-MS). External otitis samples collected from dogs were submitted to staphylococcal isolation, followed by MALDI-TOF mass spectrometry identification. The antimicrobial action was tested against the isolates using the disk-diffusion and microdilution methods. The antibiofilm activity was evaluated by CZEO-based concentrations, subMIC for biofilm formation and supraMIC against preformed biofilm, quantified by crystal violet (CV) staining and CFU counting. The chemical analysis revealed that (E)-cinnamaldehyde, eugenol and (E)-cinnamyl acetate were the main compounds in the CZEO, representing 77.42, 8.17 and 4.50%, respectively. Two strains of three different species, S. saprophyticus, S. schleiferi and S. pseudintermedius, were identified. The disk-diffusion test showed an inhibitory zone diameter, ranging from 34.0 to 49.5 mm, while the MIC and MBC values were around 500 and 1000 µg/mL. SubMIC demonstrated an inhibition on biofilm formation against 4 out the 6 strains tested. On mature biofilm, the CZEO-based supraMIC groups had slightly change on biomass, however, the biofilm cell viability decreased the CFU in 3 magnitude orders.

Palabras clave: diversidad bacteriana, carga bacteriana, contaminación con metales, normativas ambientales RESUMEN La contaminación de ambientes naturales por metales es básicamente producto de actividades antrópicas, tales como siderurgia, minería, galvanoplastia y Curtiembre es el lugar donde ocurre el proceso de curtido de pieles, no el proceso en sí de pieles y cuero. Como consecuencia, los microorganismos en los ambientes impactados se someten a condiciones estresantes, provocando una disminución de la biomasa y diversidad biológica, particularmente la bacteriana. En este estudio se reportan disminuciones estadísticamente significativas en el contenido de carbono orgánico total (70 %), actividad ureásica (54 %), biomasa bacteriana (47 %) y carga bacteriana (30-80 %) en suelos que contienen metales en niveles considerados permisibles por la legislación venezolana. El cociente respiración basal/biomasa microbiana se incrementó en 58 % respecto al suelo testigo. La diversidad bacteriana se redujo y se lograron aislar sólo 12 morfotipos en placas de agar LB suplementadas con sales ) fueron parámetros determinantes en la reducción de la diversidad y carga bacterianas. Los datos reportados deberían constituir un llamado de alerta a la autoridad ambiental venezolana para revisar y establecer los niveles permisibles de metales en ambientes naturales, de tal manera de que los parámetros bioquímicos y fisiológicos del suelo no se afecten negativamente; adicionalmente, la carga y diversidad microbianas deberían ser incluidas como bioindicadores de salud para suelos.Key words: bacterial diversity, bacterial load, contamination by metals, environmental normative ABSTRACT Contamination of natural environments by metals is basically due to anthropogenic activities such as iron and steel industries, mining, electroplating and tannery. As a A.J. Armado-Matute et al. 442consequence, proliferating microbes in such environments are subjected to stress conditions which induce decreases of the microbial diversity and biomass, particularly the bacterial one. This study reports statistical significant reductions of the total organic carbon content (70 %), urease activity (54 %), microbial biomass (47 %), and bacterial load (3080 %) in soil samples containing permissible levels of metals according to the Venezuelan legislation. Besides, the basal respiration/microbial biomass ratio increased 58 % respect to the witness soil. The bacterial diversity was severally reduced and only 12 bacterial morphotypes were isolated from agar LB plates supplemented with Cr ) were the most important parameters involved in reducing the bacterial diversity and load. The reported data should constitute an alarm call to the Venezuelan environmental authority to revise and set the metal permissible levels in natural environments, in such a way the soil biochemical and physiological parameters are not negatively affected; besides, microbial load and diversity should be included as health bioindicators to soils. INTRODUCCIÓNEl suelo es uno de ambientes na...

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