Assessment of vancomycin resistance transfer among enterococci of clinical importance in milk matrix

Resistance profile and biofilm production of Enterococcus spp., Staphylococcus sp., and Streptococcus spp. from dairy farms in southern Brazil

Milk is a high nutritional value food that helps in human development and growth. However, it can also harbor microorganisms. Therefore, the objective of this study was to isolate, identify and evaluate the resistance profile and pathogenicity factors of gram-positive cocci isolated from liners in milking rooms in the south of Rio Grande do Sul, Brazil. Biochemical and molecular tests were performed for the identification. The following were isolated: Enterococcus faecalis (10), Enterococcus faecium (4), Staphylococcus intermedius (1), Streptococcus uberis (1), and Streptococcus dysgalactiae (1). The susceptibility of isolated microorganisms to eight antibiotics was evaluated according to CLSI, and the genus that proved to be resistant to most of those was Enterococcus. In addition, all 17 isolates were able to form biofilm, which remained viable after the use of neutral, alkaline and alkaline-chlorinated detergent. The only product that was effective against biofilm of all microorganisms was chlorhexidine 2%. The results obtained highlight the importance of pre- and post-dipping tests on dairy properties, in which chlorhexidine is one of the disinfectants used. As observed, products indicated for cleaning and descaling pipes were not effective on biofilms of the different species tested.

Nisin Influence on the Antimicrobial Resistance Ability of Canine Oral Enterococci

Periodontal disease (PD) is one of the most common diseases in dogs. Although previous studies have shown the potential of the antimicrobial peptide nisin for PD control, there is no information regarding its influence in the development of antimicrobial resistance or horizontal gene transfer (HGT). Nisin's mutant prevention concentration (MPC) and selection window (MSW) were determined for a collection of canine oral enterococci. Isolates recovered after the determination of the MPC values were characterized for their antimicrobial profile and its nisin minimum inhibitory and bactericidal concentrations. The potential of vanA HGT between Enterococcus faecium CCGU36804 and nine clinical canine staphylococci and enterococci was evaluated. Nisin MPC values ranged from 400 to more than 600 μg/mL. In comparison with the original enterococci collection, the isolates recovered after the determination of the nisin MPC showed increased resistance towards amoxicillin/clavulanate (5%), vancomycin (5%), enrofloxacin (10%), gentamicin (10%) and imipenem (15%). The HGT of vanA gene was not observed. This work showed that nisin selective pressure may induce changes in the bacteria's antimicrobial resistance profile but does not influence horizontal transfer of vanA gene. To our knowledge, this is the first report of nisin's MPC and MSW determination regarding canine enterococci.