Artisanal Pico cheese as reservoir of Enterococcus species possessing virulence and antibiotic resistance properties: implications for food safety

Abstract

ABSTRACT Enterococci are part of the dominant microbiota of artisanal Pico cheese and could be used as adjunct cultures for improving this traditional dairy product. However, the genus lacks Qualified Presumption of Safety (QPS) status. The aim of this study was to assess virulence factors, antibiotic resistance and biogenic amine production in 28 autochthonous Enterococcus from Pico cheese. Isolates were identified by sequencing of the 16S rRNA gene and physiological characteristics (hemolysis, DNase, gelatinase, biogenic amine production, and antibiotic resistance), prior to phenotypic and genotypic (asa1, gelE, cylA, esp, efaA, ace, tdc, odc, hdc1, and hdc2) testing for virulence properties. All enterococci displayed antibiotic resistance, mainly to high doses of aminoglycosides (kanamycin and netilmicin). Furthermore, two of the studied isolates displayed vancomycin resistance, not attributable to vanA and vanB. No isolate produced DNase and only one was β-hemolytic, but gelatinase production was observed in 54% of the isolates. The most frequently present virulence genes were efaA (100%), gelE and tdc (86%) and ace (71%). The less represented genes were esp (46%), asa1 (43%), cylA (21%) and hdc2 (4%). No isolate was devoid of virulence factors, making them unsuitable for use as Pico cheese adjunct cultures. Our results stress the importance of assessing the safety of each E. faecalis isolate from artisanal cheeses intended for use in food fermentations.