Persistence of glycopeptide resistance determinants in Enterococcus faecium in the absence of antibiotic selection

Project leader(s)   Arnfinn Sundsfjord and Gunnar S Simonsen

Co-workers / Project staff
Pål Johnsen, Hege Sletvold, Marit Sørum, Torill Rosvoll, Bettina Aasnes, Hilde Kruse, Kristin H Dahl, Johanna E Sollid, Kaare Nilssen

Main Objects:
Reservoirs of VanA-type glycopeptide resistant enterococci (GRE) were discovered in food animals in several European countries in the early 1990s. The findings were causally linked to the use of avoparcin, a glycopeptide animal growth promoter. Avoparcin resistance mediates cross-resistance to vancomycin, a clinically important glycopeptide antibiotic considered as a drug of last resort in the treatment of multiresistant Gram-positive bacteria. Several studies have provided indirect evidence for the transfer of GRE and/or their resistance determinants from animal reservoirs to humans. The EU ban on avoparcin usage in 1997 was introduced to reduce the human exposure to GRE, also allowing us to monitor the dynamics of antibiotic resistance in large scale after the removal antibiotic selection. Follow-up studies have shown a reduction in the proportion of glycopeptide resistance among faecal enterococci isolated from chicken, as well as in the prevalence of faecal carriage among healthy humans in the community. However, considering the large amount of enterococci in the faecal flora of poultry (~ 10^7-9 CFU/g faeces) the reported one log reduction of faecal GRE in poultry implies a significant persistent reservoir of GRE. This has been confirmed in recent Danish and Norwegian studies showing a high prevalence of animals excreting GRE in farms exposed to avoparcin several years after the ban. These observations indicate a long-term reservoir of glycopeptide resistance determinants to which humans have been, and are still, regularly exposed. The main objectives are to monitor the GRE reservoir in Norwegian avoparcin-exposed farms and to elucidate the mechanism(s) for this intriguing long-term persistence in the absence of overt antibiotic selection.

Collaborators / Partners
Marit Sørum and Hilde Kruse, National Veterinary Institute, Oslo, Norway.

Funding
The European Commission, contract QLK2-CT-2002-00843 “ARTRADI”

Publications
1. Haaheim H, Dahl KH, Simonsen GS, Olsvik Ø, Sundsfjord A. Long PCRs of transposons in the structural analysis of genes encoding acquired glycopeptide resistance in enterococci. BioTechniques 1998;24:432-37.
2. Simonsen G, Haaheim, Kruse H, Dahl KH, Løvset A, Olsvik Ø, Sundsfjord A. Transmission of VanA-type Vancomycin Resistant Enterococci and vanA Resistance Elements Between Chicken and Humans at Avoparcin-Exposed Farms. Microbial Drug Resist 1998;4:313-18.
3. Harthug S, Digranes A, Simonsen GS, Olsvik Ø, Sundsfjord A, Natås OB, Harr E, Gaustad P, Høiby EA, Svarva PE. Infections caused by multidrug resistant enterococci in Norway (In Norwegian). Tidsskr Nor Lægeforen 1998;118:4070-3.
4. Simonsen GS, Andersen BM, Digranes A, Harthug S, Jacobsen T, Lingaas E, Natås OB, Olsvik Ø, Ringertz SH, Skulberg A, Syversen G, Sundsfjord A. Low fecal carrier rate of vancomycin resistant enterococci in Norwegian hospital patients. Scand J Inf Dis 1998;30:465-68.
5. Borgen K, Simonsen GS, Sundsfjord A, Wasteson Y, Olsvik Ø, Kruse H. Extensive persistence of VRE on Norwegian poultry farms 3 years after the avoparcin ban. J Applied Environmental Microbiology 2000; 89:478-85.
6. Simonsen GS, Myhre MRM, Dahl KH, Olsvik Ø, Sundsfjord A. Typability of Tn1546-like elements in vancomycin resistant enterococci using long-range PCRs and specific analysis of polymorphic regions. Microbial Drug Resistance 2000;6:49-58.
7. Sundsfjord A, Simonsen GS, Courvalin P. Human infections caused by glycopeptide-resistant Enterococcus: are they a zoonosis ? Clin Microbiol infection 2001;7;S4:16-33.
8. Johnsen P, Simonsen GS, Olsvik Ø, and Sundsfjord A. Stability, persistence and evolution of plasmid-encoded vanA glycopeptide resistance in enterococci in the absence of antibiotic selection in vitro and in gnotobiotic mice. Microbial Drug Res 2002;8:161-70.
9. Johnsen PJ, Østerhus JI, Sletvold H, Sørum M, Kruse H, Nielsen K, Simonsen GS, Sundsfjord A. Persistence of animal and human glycopeptide resistant enterococci on two Norwegian poultry farms formerly exposed to avoparcin is associated with a widespread plasmid-mediated vanA-element within a polyclonal Enterococcus faecium population. Appl Environ Microbiol 2005;71:159-68.