Emerg Infect DisEmerging Infect. DisEIDEmerging Infectious Diseases1080-60401080-6059Centers for Disease Control and Prevention22172303331116910-158410.3201/eid1712.101584Letters to the EditorLetterPorcine and Human Community Reservoirs of Enterococcus faecalis, DenmarkCommunity Reservoirs of E. faecalisLarsenJesperSchønheyderHenrik C.SinghKavindra V.LesterCamilla H.OlsenStefan S.PorsboLone J.Garcia-MiguraLourdesJensenLars B.BisgaardMagneMurrayBarbara E.HammerumAnette M.Statens Serum Institut, Copenhagen, Denmark (J. Larsen, C.H. Lester, S.S. Olsen, A.M. Hammerum);Aarhus University Hospital, Aalborg, Denmark (H.C. Schønheyder);University of Texas Medical School, Houston, TX, USA (K.V. Singh, B.E. Murray);Technical University of Denmark, Søborg, Denmark (L.J. Porsbo);Technical University of Denmark, Kgs. Lyngby, Denmark (L. Garcia-Migura, L.B. Jensen);University of Copenhagen, Frederiksberg, Denmark (M. Bisgaard)Address for correspondence: Jesper Larsen, Department of Microbiological Surveillance and Research, Statens Serum Institut, Artillerivej 5, DK-2300 Copenhagen S, Denmark; email: jrl@ssi.dk122011171223952397Keywords: Enterococcus faecalisendocarditisdisease reservoirsswinemultilocus sequence typingelectrophoresisgelpulsed-fieldbiofilmsvirulence factorsdrug resistancebacteria

To the Editor: Enterococcus faecalis, which exists commensally in the gut in warm-blooded animals and humans, is an opportunistic pathogen that causes a variety of community-acquired and health care–associated infections, such as urinary tract and intraabdominal infections, bacteremia, and endocarditis (1). Only a few studies have assessed the relationships between clinical E. faecalis strains; strains endemic to the health care setting; and community strains residing in humans, animals, or animal-origin food (2).

Recently we showed that the emergence of high-level gentamicin-resistant (HLGR) E. faecalis among patients with infective endocarditis (IE) coincided with an increase in HLGR E. faecalis in the pig population in Denmark (3). The majority of isolates belonged to the same clonal group (sequence type [ST] 16), suggesting that pigs constitute a community reservoir of HLGR E. faecalis. We investigated human and porcine community reservoirs of other E. faecalis clonal types associated with IE in humans in Denmark.

A total of 20 consecutive gentamicin-susceptible E. faecalis isolates were obtained from IE patients in North Denmark Region during 1996–2002 (Table A1). Cases of IE were classified as definite (n = 12) or possible (n = 8) according to the modified Duke criteria (4). A case of community-acquired E. faecalis infection (n = 6) was defined in accordance with strict criteria applied for methicillin-resistant Staphylococcusaureus (5); otherwise, cases were deemed to be health care associated (n = 14) (Table A1). HLGR ST16 isolates recovered from 2 IE patients during the study period have been characterized (3) and were excluded from the present study.

Using multilocus sequence typing (6), we identified 14 STs among the 20 IE isolates (Table A1), then compared them with STs from 2 collections of E. faecalis isolates collected as part of the Danish Integrated Antimicrobial Resistance Monitoring and Research Program (www.danmap.org): 1) all 14 isolates recovered from community-dwelling humans in North Denmark Region during 2002–2006 with approval from the local ethics committee ([KF] 01-006/02), which were classified into 10 STs in this study (Table A1); and 2) 19 pig isolates from 2001 that were shown in a previous study to belong to 12 STs (7).

Among the 14 STs identified in IE isolates, 4 (ST19, ST21, ST72, and ST306) and 2 (ST40 and ST97) were also found among isolates from community-dwelling humans and pigs, respectively (Table A1). Isolates belonging to these 6 STs were further characterized by pulsed-field gel electrophoresis (PFGE) by using SmaI and grouped into PFGE pulsotypes as described (3). STs and PFGE pulsotypes (A–F) were largely concordant (ST97:A, ST72:B, ST19:C, ST40:D, ST21:E, and ST306:F), except for 2 isolates belonging to ST72 and ST40, for which PFGE banding patterns (U1 and U2, respectively) were unrelated to the major PFGE pulsotypes (A–F), and 1 ST306 isolate exhibiting the ST21-like PFGE banding pattern E (Table A1).

These findings confirm the genetic relatedness of IE isolates with those from community-dwelling humans (ST72:B, ST19:C, ST21:E, and ST306:F) and pigs (ST97:A and ST40:D). Seven (64%) of 11 IE isolates belonging to these 6 clonal types originated from IE patients with health care–associated risk factors (Table A1), which suggests that health care users are predisposed to colonization and infection with E. faecalis strains residing in human and porcine community reservoirs.

Previous reports have shown that epidemiologically distinct E. faecalis populations differ in terms of biofilm formation, virulence gene content, and antimicrobial drug susceptibility profiles (2,8). Therefore, we characterized all isolates with respect to these traits. Isolates were categorized into strong, medium, weak, and nonbiofilm formers by using the method of Mohamed et al. (8). The presence of 12 virulence-associated and pathogenicity island genes (ebpA, gelE, ef1824, hylA, ef1896, ef2347, ef2505, hylB, ace, cbh, esp, and ef0571) was investigated by using colony lysates and probes that have been described elsewhere (9). The antimicrobial drug susceptibility profiles (ampicillin, chloramphenicol, ciprofloxacin, erythromycin, gentamicin, kanamycin, linezolid, penicillin, streptomycin, teicoplanin, tetracycline, and vancomycin) were determined by the Sensititre system (Trek Diagnostic Systems, East Grinstead, UK) in accordance with Clinical and Laboratory Standards Institute guidelines (10). The isolates were generally homogenous within each clonal type in terms of biofilm formation, presence of virulence-associated and pathogenicity island genes, and resistance profiles (Table A1), further supporting that IE isolates are genetically related to those from community-dwelling humans and pigs, respectively. Notably, most IE isolates were susceptible to ampicillin (100%), penicillin (100%), vancomycin (100%), high-level gentamicin (100%), and high-level streptomycin (80%), which are the drugs of choice in therapeutic regiments for E. faecalis endocarditis.

In conclusion, our results suggest that the normal intestinal microflora of humans and pigs are community reservoirs of clinical E. faecalis and link 2 porcine-origin clonal types of gentamicin-susceptible E. faecalis, ST97:A, and ST40:D to IE in humans in Denmark. This finding strengthens existing evidence that pigs can be a source of serious infections in humans.

Suggested citation for this article: Larsen J, Schønheyder HC, Singh KV, Lester CH, Olsen SS, Porsbo LJ, et al. Porcine and human community reservoirs of Enterococcus faecalis, Denmark [letter]. Emerg Infect Dis [serial on the Internet]. 2011 Dec [date cited]. http://dx.doi.org/10.3201/eid1712.101584

Acknowledgments

We thank Karin S. Pedersen for help with antimicrobial drug susceptibility testing and genotyping and Lena Mortensen for providing clinical isolates.

This work was supported by grant 271-06-0241 from the Danish Medical Research Council, the Danish Ministry of Family and Consumer Affairs, and the Danish Ministry of the Interior and Health as part of the Danish Integrated Antimicrobial Resistance and Research Program, and the European Union Sixth Framework Program “Approaches to Control Multiresistant Enterococci: Studies on molecular ecology, horizontal gene transfer, fitness and prevention” under contract LSHE-CT-2007-037410.

Origins and molecular and phenotypic characteristics of <italic>Enterococcus</italic> <italic>faecalis</italic> isolates*
ID (other name)Origin†SettingSampling
yearMLST†PFGE‡Biofilm formationVirulence-associated genesPAI genesResistance profile
31438-1IE patientHA199797AWeakebpA gelE hylA ef1896 ef2505 acecbhNone
130529IE patientHA200097AWeakebpA gelE hylA ef1896 ef2505 acecbhNone
67190IE patientCA200297AWeakebpA gelE hylA ef1896 ef2505 acecbhNone
7330616-3 (D30)PigNA200197AWeakebpA gelE hylA ef1896 ef2505 acecbhNone
28137IE patientHA199672BNoneebpA gelE ef1824 hylA ef2505 hlyB acecbhNone
7684IE patientHA199772BWeakebpA gelE ef1824 hylA ef2505 hlyB acecbhNone
33873IE patientHA200272BMediumebpA gelE ef1824 hylA ef2505 hlyB acecbhNone
1293CD humanNA200372BMediumebpA gelE ef1824 hylA ef2505 hlyB acecbhNone
3527CD humanNA200672BMediumebpA gelE ef1824 hylA ef2505 hlyB acecbhNone
1745CD humanNA200472U1WeakebpA gelE ef1824 hylA ef2505 hlyB acecbhTET
43674IE patientCA199919CMediumebpA gelE ef2505 hlyB aceNoneERY TET
2247CD humanNA200419CMediumebpA gelE ef2505 hlyB acecbh espCIP ERY TET
54869IE patientHA199740DWeakebpA gelE hylA ef2505 hlyB acecbhKAN STR TET
7330082-2 (D1)PigNA200140DMediumebpA gelE hylA ef2505 hlyB acecbh espNone
7330321-1 (D27)PigNA200140DMediumebpA gelE hylA ef2505 hlyB acecbh espCHL ERY KAN STR TET
7331063-5 (D37)PigNA200140DNoneebpA gelE hylA ef2505 hlyB acecbhSTR
7330887-1 (D32)PigNA200140U2NoneebpA gelE hylA ef2505 hlyB acecbhERY STR
26669IE patientHA199821EWeakebpA gelE hylA ef2505 hlyB acecbhNone
3162CD humanNA200521EWeakebpA gelE hylA ef2505 acecbh espTET
105049IE patientCA1997306EMediumebpA gelE hylA ef1896 ef2505 acecbh espNone
127801IE patientCA1999306FMediumebpA gelE hylA ef1896 ef2505 acecbh espNone
2421CD humanNA2004306FMediumebpA gelE hylA ef1896 ef2505 acecbh espNone
57690IE patientHA200022NAWeakebpA gelE ef1824 hylA ef2505 hlyB acecbhNone
20505-1IE patientHA200030NAWeakebpA gelE hylA ef1896 ef2505 aceespTET
100087IE patientHA199941NAWeakebpA gelE hylA ef1896 ef2505 acecbh espERY KAN STR TET
105158IE patientHA199755NAMediumebpA hylA ef1896 ef2505 hlyB acecbh espCHL ERY KAN STR TET
134125IE patientHA200055NAStrongebpA hylA ef1896 ef2505 hlyB acecbh espCHL ERY KAN STR TET
29783IE patientHA199981NAMediumebpA gelE ef1824 hylA ef2505 hlyB acecbh ef0571None
120903IE patientCA1999192NAMediumebpA gelE ef1824 hylA ef2505 hlyB aceNoneTET
107137IE patientHA2001241NAWeakebpA gelE ef1824 hylA ef2505 hlyB acecbh ef0571None
83232IE patientCA1997326NAStrongebpA gelE hylA ef1896 ef2505 acecbh espNone
1149CD humanNA2003133NAStrongebpA hylA ef1896 ef2505 acecbhTET
3392CD humanNA2005133NAMediumebpA hylA ef1896 ef2505 acecbhNone
1732CD humanNA2003141NANoneebpA gelE ef1824 hylA ef2505 hlyB aceNoneCIP
1028CD humanNA2003168NAStrongebpA gelE ef1824 hylA ef2505 hlyB acecbhNone
1309CD humanNA2003168NAStrongebpA gelE ef1824 hylA ef2505 hlyB acecbhNone
1413CD humanNA2003199NAMediumebpA gelE ef1824 hylA ef2505 acecbhNone
2174CD humanNA2004206NAWeakebpA hylA ef2505 acecbhTET
2041CD humanNA2004327NAWeakebpA hylA ef2505 acecbhTET

*MLST, multi-locus sequence typing; PFGE, pulsed-field gel electrophoresis; PAI, pathogenicity island; IE, infective endocarditis; CD, community-dwelling; HA, healthcare-associated infection; CA, community-acquired infection; NA, not applicable; CHL, chloramphenicol; CIP, ciprofloxacin; ERY, erythromycin, KAN, kanamycin; STR, streptomycin; TET, tetracycline.
†STs from 5 pig isolates (in italics) have been published previously (7); the remaining 14 pig isolates belonging to other STs (ST1, ST6, ST16, ST26, ST47, ST63, ST96, ST98, ST99, and ST100) were not included in further analysis.
‡Isolates with similar PFGE banding patterns (>82% relatedness) received the same letter designation (A–F) to reflect their genetic relatedness; highly divergent PFGE banding patterns were designated as unique (U) types (U1 and U2).

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