Abstract
Enterococci represent the most controversial group of dairy bacteria. They are found to be the main constituent of many traditional Mediterranean dairy products and contribute to their characteristic taste and flavor. On the other hand, during the last 50 years antibiotic-resistant enterococci have emerged as leading causes of nosocomial infections worldwide. The aim of this study was to determine the diversity, technological properties, antibiotic susceptibility and virulence traits of 636 enterococci previously isolated from 55 artisan dairy products from 12 locations in the Western Balkan countries (WBC) of Serbia, Croatia and Bosnia and Herzegovina. All strains were identified both by microbiological and molecular methods. The predominant species was Enterococcus durans, followed by Enterococcus faecalis and Enterococcus faecium. Over 44% of the isolates were resistant to ciprofloxacin and erythromycin, while 26.2% of the isolates were multi-resistant to three or more antibiotics belonging to different families. 185 isolates (29.1%) were susceptible to all 13 of the antibiotics tested. The antibiotic-susceptible isolates were further tested for possible virulence genes and the production of biogenic amines. Finally, five enterococci isolates were found to be antibiotic susceptible with good technological characteristics and without virulence traits or the ability to produce biogenic amines, making them possible candidates for biotechnological application as starter cultures in the dairy industry.
Highlights
Bacteria of the genus Enterococcus, or enterococci, are considered lactic acid bacteria (LAB) (Schleifer and Ludwig, 1995)
The results showed that the dairy samples analyzed contained five Enterococcus species: E. durans, E. faecalis, E. faecium, E. italicus, and E. avium
The highest diversity and the lowest index of dominance of enterococci species were scored by samples from cheeses from the Prigorje region, Croatia (H = 1.61; D = 0.36) and Pirot region, Serbia (H = 1.5; D = 0.34), where four of five enterococci species were identified (E. durans, E. faecalis, E. faecium, E. italicus)
Summary
Bacteria of the genus Enterococcus, or enterococci, are considered lactic acid bacteria (LAB) (Schleifer and Ludwig, 1995). Enterococcus faecium, Enterococcus faecalis, and Enterococcus durans are the most prevalent species of enterococci in raw milk cheeses (Terzic-Vidojevic et al, 2007, 2009a,b, 2013, 2014a,b; Golicet al., 2013) They break down lactose and citrate during cheese ripening, which leads to Antibiotic susceptibility of enterococcal isolates the production of various volatile compounds, such as acetaldehyde, acetoin, diacetyl, and ethanol, which are responsible for the formation of the unique aroma and flavor of the final product (Andrighetto et al, 2001; Sarantinopoulos et al, 2001; Giraffa, 2002; Abeijón et al, 2006; FoulquiéMoreno et al, 2006). Each strain that is intended to be used in a starter culture should be tested individually before any use in food or medicine, must not possess a single virulence factor and should be susceptible to relevant clinical antibiotics (Domig et al, 2003; Franz et al, 2003)
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