Bacteriocin-like inhibitory substances (BLIS) produced by wild lactic bacteria with effect on resistant methicillin-Staphylococcus aureus

VASEK, OM, A MARTURET, JA VALENZUELA LÓPEZ

Málaga

Conferencia; BioMicroWorld 2018 Conference; 2018

BioMicroWorld

Staphylococcus aureus (SA) is a microorganism of particular importance because of its ability to cause a wide range of diseases in humans, from a simple infection to inflammation of the meninges and septicaemia, and its capacity to adapt to diverse environmental forms. In addition, S. aureus causes inflammation of the mammary gland in bovine, then, the milk and milk products may become contaminated with SA through milking of infected animal. Certain strains of SA developed resistance known as methicillin resistant Staphylococcus aureus (MRSA). In Argentina, the prevalence of MRSA reached 54%, with predominance of the MRSA phenotype from the community setting (37%) on MRSA from the hospital setting (17%). However, a quarter of Associated to Community-MRSA infections are invasive and their treatment can be difficult.42 strains of presumptive Staphylococcus spp. were isolated and purified from human and food (raw milk and artisanal cheeses) samples. Phenotypic identification, according to Bennett and Lancette [1] showed that among the 42 isolates, 29 were classified as SA coagulase (+), 7 as Staphylococcus epidermidis and 6 as Staphylococcus spp. These strains were challenged against 5 strains of Lactococcus (Lc.) lactis subsp. lactis autochthonous and potentially bacteriocinogenic, using the agar well diffusion assay AWDA [2]. The growth of SA coagulase (+) strains was inhibited by the metabolites generated by 3 strains of Lc. lactis subsp. lactis.The profile of antibiotic sensitivity was made according to Coyle [3] and included Ampicillin, Bacitracin, Cefoxitin, Gentamicin, Nalidixic acid, Nitrofurantoin, Novobiocin, Oxacillin, and Vancomycin. 29 SA strains corresponded with methicillin resistant (MRSA), 16 for them isolated from humans and 13 from raw milk and artisanal cheeses. Lc. lactis subsp. lactis 35c BiMIA-UNNE (108 UFC.mL-1) presented the highest activity, inhibiting the growth of 19 MRSA strains, the strain 140c BiMIA-UNNE inhibited 6 MRSA strains and the strain 207c BiMIA-UNNE (108 UFC.mL-1) inhibited 8 MRSA strains, some of them with multiple sensitivity. Cell density of the producing strains was 108 UFC.ml-1 and the sensitive strains was 107 UFC. mL-1. The counts were performed on Elliker agar and Baird Parker agar, respectively.Acid inhibition was ruled out by the adjustment of pH samples to pH 6.5 with 1 N of NaOH. Inhibitory activity from hydrogen peroxide was ruled out by the addition of catalase (300 IU.mL-1). The antagonistic activities of these samples were determined for each isolate by the AWDA as it was previously mentioned using MRSA strains as indicator microorganism. Proteinaceous nature of the antimicrobial compounds was confirmed by the addition of Trypsin, Proteinase K and alfa-chymotrypsin at a final concentration of 1 mg.mL-1 to the cultures. The samples were incubated for 3 h at 37 °C and immediately after, the residual activity was determined by the AWDA for the indicator strains mentioned above.These results will allow evaluating the mechanism of this antagonism and the concrete possibilities of industrial application in the alimentary or clinical field. However, and due to its restricted spectrum of activity, these antimicrobial metabolites have greater possibilities to be applied in the pharmaceutical industry than in the food industry.