Implications of multiple antimicrobial-resistant enterococci associated with the poultry environment

Poultry are increasingly being associated with carriage of multiresistant organisms that may cause disease in humans. Among these organisms are the enterococci, not regarded as a common cause of hospital-acquired infections. The use of antimicrobials for growth promotion in poultry production envronments may facilitate the dissemination of resistance to Enterococcus spp. that have the potential to be clinically significant. To assess descriptively the degree of multiresistant enterococci in the poultry environment of the Delmarva (Delaware-Maryland-Virginia) East Coast region of the USA, litter samples from regional commercial poultry houses and transport container swabs from processing facilities were cultured for Enterococcus spp. Using a microtiter plate adaptation of a conventional biochemical screen, the predominant species identfied were E. faecalis (61.2%), E. faecium (18.6%) and E. gallinarum (2.4%). Resistance to the cephalosporin, macrolide and tetracycline classes of antimicrobials was uniform with broader resistance to penicillin and derivatives present in a majority of E. faecium isolates. High-level streptomycin resistance was evident in close to 30% of all isolates with a majority of E. faecalis variants possessing resistance. High-level gentamicin resistance was detected at a low frequency (2.6%) only within the E. faecalis group with resistance to low-level gentamicin levels present in a majority of both the E. faecalis group and subsets of E. faecium. No unexpected vancomycin resistance was detected. Of particular interest was resistance to the streptogramin quinupristin-dalfopristin (Q-D or Synercid), which was present in 70.4% of E. faecium and E. faecium variants.