Diversity and antibiotic susceptibility of autochthonous dairy enterococci isolates: are they safe candidates for autochthonous starter cultures?

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.

New Insight into Biofilm Formation Ability, the Presence of Virulence Genes and Probiotic Potential of Enterococcus sp. Dairy Isolates

“…Due to the controversial status of enterococci, the focus of this study was the evaluation of presence of antibiotic resistance, virulence genes, and biofilm formation in 75 previously isolated dairy enterococci from WBC region (Table S1 , Figure S1 ; Terzić-Vidojević et al, 2015 ) and their correlation with the origin and phylogenetic relatedness. To our knowledge, this is the first study combining data on virulence and probiotic traits in order to improve our understanding of the dairy products as a potential reservoir of virulent strains, as well as the implications for the safety use of dairy enterococci isolates as potential probiotics.…”

“…Although all 75 strains were previously determined as antibiotic susceptible, according to the results obtained by disc diffusion method (Terzić-Vidojević et al, 2015 ), the antibiotic susceptibility to nine of the most clinically relevant antibiotics of 56 enterococci strains without haemolytic and gelatinase activity were additionally tested by microdilution test, according to CLSI. In total, only 23 out of 56 strains were antibiotic susceptible, while 57% were resistant to ciprofloxacin (27 strains) or gentamicin (6 strains).…”

“…The 75 previously isolated enterococci dairy isolates belonging to five distinct species were used (Table S1 ; Terzić-Vidojević et al, 2015 ). Enterococci were grown in M17 broth (Merck, GmbH, Darmstadt, Germany) supplemented with glucose (0.5% w/v) (GM17) at 37°C.…”

“…Our previous results based on analysis of 50 antibiotic resistant enterococci in environmental waters of Belgrade (Serbia) suggested the anthropogenic impact on the spread of antibiotic resistance genes among enterococci in urban surface waters that is most likely attributed to the uncontrolled use of antibiotics (Veljović et al, 2015 ). However, our work related to dairy enterococci isolates revealed that autochthonous dairy products from the Western Balkan Countries (WBC) region are a rich source of novel enterococci strains with substantial genetic, metabolic and technological potential, although the presence of antibiotic resistance and virulence genes were revealed, pointing out that the determination of the safety status of each potential probiotic enterococci strain is mandatory in order to prevent the potential risks of their administration to humans and animals (Terzić-Vidojević et al, 2015 ).…”

Novel Aggregation Promoting Factor AggE Contributes to the Probiotic Properties of Enterococcus faecium BGGO9-28

“…Considering the importance of aggregation phenomena for human health, the laboratory collection of enterococci was screened for strains exhibiting strong aggregation ability for further analysis. Fourteen Enterococcus strains were selected from among 636 examined enterococcal isolates (Terzić-Vidojević et al, 2015 ) from a laboratory collection, based on their ability to cause auto-aggregation of the cells, using an aggregation visual assay. All of them were isolated from artisanal homemade cow's milk cheeses, produced in households of the Golija and Valjevo mountain regions of the Republic of Serbia (Table 1 ).…”