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. 2021 Mar 2;11(3):661.
doi: 10.3390/ani11030661.

Molecular Characteristics of Enterococcus faecalis and Enterococcus faecium from Bulk Tank Milk in Korea

Sunghyun Yoon  1   2 , Young Ju Lee  2
Affiliations

Molecular Characteristics of Enterococcus faecalis and Enterococcus faecium from Bulk Tank Milk in Korea

Sunghyun Yoon et al. Animals (Basel). .

Abstract

Enterococci are considered to be environmental mastitis-causing pathogens that can easily spread antimicrobial resistance or virulence genes via horizontal transfer. In this study, the molecular characteristics of enterococci from bulk tank milk were investigated to assess the importance of dairy herd management. A total of 338 enterococci (305 Enterococcus faecalis and 33 Enterococcus faecium) were isolated from 1584 batches of bulk tank milk samples from 396 farms affiliated with four dairy companies in Korea, and significant differences (40.6-79.7%) (p < 0.05) in the prevalence of enterococci were observed in the samples from different companies. Enterococci showed the highest resistance to tetracycline (TET) (73.4%), followed by doxycycline (DOX) (49.7%) and erythromycin (ERY) (46.2%), while two enterococci isolates showed resistance to vancomycin (VAN). Among 146 tetracycline (TET) and ERY-resistant enterococci, each 50 (19.4%) enterococci carried combination-resistance and transposon gene types erm(B) + tet(M) + IntTn and erm(B) + tet(L) + tet(M) + IntTn, respectively. The virulence genes such as ace (99.0%), efaA (97.7%), cad1 (95.7%), and gelE (85.9%) were highly conserved in E. faecalis and significantly predominated over E. faecium (p < 0.001). Our results indicate that pathogens from bulk tank milk can also become a reservoir for the dissemination of antimicrobial resistance and virulence factors through cross-contamination processes.

Keywords: Enterococcus; antimicrobial resistance; bulk tank milk; transposon; virulence.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Figures

Figure 1
Figure 1
Prevalence of Enterococcus faecalis and Enterococcus faecium in bulk tank milk samples from four dairy companies. Values not sharing a common subscript letter (a, b, c) are statiscally different (p < 0.05).
Figure 2
Figure 2
Distribution of multidrug resistant Enterococcus faecalis and Enterococcus faecium in bulk tank milk from four dairy companies. Values not sharing a common subscript letter (a,b) are statistically different (p < 0.05).
See this image and copyright information in PMC

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