The occurrence of vanA-positive Enterococcus faecium in food animals and meat has been associated with the use of the glycopeptide avoparcin for growth promotion.1vanA is relatively common in E. faecium isolates from meat and animals, whereas this resistance trait is rarely found in Enterococcus faecalis. Most vanA-positive E. faecalis have been isolated from hospitalized patients. vanA-positive E. faecalis with relation to meat or animals were found to be associated with poultry production in Asia and New Zealand.2,3
Extended sampling of poultry meat in the Danish Integrated Antimicrobial Resistance Monitoring and Research Programme (DANMAP) was performed in 2005 through 2006 resulting in 3116 samples collected from chicken meat (imported meat, n = 1060 and Danish meat, n = 1149) and turkey meat (imported meat n = 862 and Danish meat, n = 45). Enterococci were isolated without selective enrichment and identified as previously described in DANMAP 2006.4 No vancomycin-resistant E. faecalis (VREF) isolates were obtained from chicken meat. Three VREF were isolated from imported turkey meat (0.7%). The turkey meats with VREF originated from at least two different German slaughterhouses. The three VREFs were isolated in three different regions of Denmark, in October 2005, December 2005 and March 2006. To our knowledge, VREF has not been detected in turkeys before. Faecal samples from 525 healthy human volunteers were collected from March 2002 through December 2006. The Scientific Ethics Committee for the Copenhagen and Frederiksberg municipalities approved the protocol [(KF) 01–006/02]. Two VREF isolates were isolated from healthy human volunteers using a vancomycin-resistant enterococci selective method as previously described in DANMAP 2005.4 One VREF isolate was obtained in October 2005 from a male living in Jutland, Denmark, who had been travelling to Thailand, whereas the other VREF isolate was obtained in November 2005 from a woman with Japanese citizenship residing in Zealand, Denmark. For comparison, three vancomycin-resistant E. faecium isolates were obtained during the same period.
The vanA-positive E. faecalis isolates from turkey meat and healthy human volunteers were compared with the only Danish clinical vanA-positive E. faecalis isolate received at the Statens Serum Institut during the last 6 years. The clinical isolate was obtained from a male patient with leukaemia, hospitalized in 2003 for an allogeneic bone marrow transplantation. The patient was treated with sulphonamide/trimethoprim and ceftazidime for prophylaxis and with vancomycin due to a staphylococcal bloodstream infection. After the transplantation, VREF was isolated from blood cultures and in faecal swabs. The VREF infection was treated with ampicillin for ∼1 month until blood cultures and faecal swabs were negative.
All six VREF isolates were resistant to vancomycin/teicoplanin, tetracycline and erythromycin encoded by vanA, tet(M) and erm(B), respectively. All six isolates had multilocus sequence typing (MLST) type ST116. PFGE showed highly similar gel patterns with less than three band differences, indicating a clonal relationship. The resistance profile encoded by the resistance genes vanA, tet(M) and erm(B) has previously been reported in clonally related VREF from human patients, broilers and a dog in New Zealand.2,5
VREF has never been isolated from retail meat in Denmark, even though retail samples of pork, broiler meat and beef have been collected in Denmark for the past 11 years. Turkey meat, on the other hand, has not been routinely sampled in DANMAP. Thus, only 67 turkey meat samples (in DANMAP 1997 and DANMAP 2001) have been collected.4 The finding of 0.7% vancomycin resistance in E. faecalis from imported turkey meat may seem low, but the finding of clonally related VREF from faecal samples from human volunteers during the same period and a hospitalized patient a couple of years before suggests imported turkey meat as a source for VREF in humans. The patient with the allogeneic bone marrow transplantation was treated with several antimicrobial agents that may have selected for the VREF infection. The patient had VREF-positive faecal swabs that could indicate a faecal origin of the VREF blood infection. An E. faecalis isolate with MLST type ST116 has only been detected once before in the MLST database consisting of 350 E. faecalis isolates, i.e. from a catheter from a patient in Havana, Cuba (Rob Willems, University Medical Center Utrecht, personal communication). Whether this type is more likely to cause infection is unknown.
In the European Union, avoparcin has not been approved for use in animal production since 1999, whereas tetracyclines and macrolides are extensively used for animal production and also for the treatment of infections in humans. The use of tetracycline and macrolide may co-select for VREF.
To our knowledge, vanA-positive E. faecalis isolates have not been previously detected in healthy humans in the community or in retail meat in Europe.
In conclusion, imported turkey meat containing VREF may be a source of VREF in the gut of healthy human subjects. The VREF from the intestine can cause infections if an individual is intensively treated with antimicrobial agents due to other severe illness.
This work was supported by 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 Monitoring and Research Programme (DANMAP), the Danish Research Agency ref. no. 274-05-0117 and the European Union Sixth Framework Programme ‘Approaches to Control Multiresistant Enterococci (ACE): Studies on molecular ecology, horizontal gene transfer, fitness and prevention’ under contract LSHE-CT-2007-037410.
None to declare.
We would like to thank Karin S. Pedersen and Frank Hansen at Statens Serum Institut and Inge M. Hansen at The National Food Institute, DTU, for excellent technical assistance. We thank Professor Henrik Schønheyder for helpful comments.