Bactericidal activity and synergy studies of peptide AP-CECT7121 against methicillinresistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium isolated from bovine mastitis

Abstract

Bovine mastitis impacts negatively on animal production and on the quality of milk. AP-CECT7121, anantimicrobial peptide produced by Enterococcus faecalis CECT7121, shows a variety of interesting biological properties(e.g. immunomodulation, anti-infective action and food bio-preservative activity) of potential use in clinical practice withoutundesirable side effects. It is considered a bacteriocin, but has a wide spectrum of bactericidal activity against Grampositivebacteria. The aim of this study was to evaluate the bactericidal activity of AP-CECT7121 alone and withgentamicin against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium isolatedfrom bovine mastitis. 11 methicillin-resistant Staph.aureus and 4 vancomycin-resistant Ent. faecium strains isolated from15 different mastitic dairy cows were tested. Animals from four dairy operations located in Province of Buenos AiresArgentina,during the period 2014-2015 were included. AP-CECT7121 (12 mg/L) potency was assessed by time-killcurves alone or with sub-inhibitory concentrations of gentamicin (MIC/4). All tested staphylococcal isolates weresusceptible to gentamicin (MIC ≤ 4 mg/L); enterococci not shown high level gentamicin resistance (MIC < 500 mg/L). A100 µL sample was used to determine colonies counts at 0, 2, 4, 8 and 24 h of incubation. AP-CECT7121 exhibitedbactericidal activity against all enterococci tested (- 4.3 to - 6.2 log10 CFU/mL). Among staphylococci, AP-CECT7121 wasbactericidal against 7/11 strains (- 3.8 to ? 4.9 log10 CFU/mL). Drug interactions with gentamicin showed early synergy (4-8 h) for all staphylococci and synergy (8/11 strains) and indifference (3/11 strains) at 24 h. The activity of AP-CECT7121with gentamicin was slightly enhanced against enterococci. AP-CECT7121 showed bactericidal activity alone against allenterococci and most of staphylococci. Synergy with gentamicin was detected against staphylococci. AP-CECT7121constitutes an attractive candidate for use as a natural therapeutic tool for the control and prevention of bovine mastitisproduced by multi-resistant bacteria like Staph.aureus and vancomycin-resistant Ent. faecium.