Enterococcus Species: Prevalence and Antibiotic Resistance Characteristics in Wild Raptors Pre- and Post-Antibiotic Treatment
American Association of Zoo Veterinarians Conference 2005
Judilee Marrow1, BS; Julia Whittington2, DVM; Lois Hoyer3, PhD; Carol Maddox3, MS, PhD
1College of Veterinary Medicine, University of Illinois, Urbana, IL, USA; 2Wildlife Medical Clinic, University of Illinois, Urbana, IL, USA; 3Department of Veterinary Pathobiology, University of Illinois, Urbana, IL, USA


Among potential pathogens, Enterococcus spp. have been implicated as indicator bacteria species for the detection of antimicrobial resistance. A normal inhabitant of gastrointestinal tracts, Enterococcus has worldwide distribution in human, mammalian, and avian hosts. Enterococcus is cited as the cause of 10% of all nosocomial infections in humans.1 Urbanization and habitat encroachment have led to an increase in human and wildlife interaction, and antimicrobial resistance is a point of concern in both human and animal medicine. The source of antibiotic-resistant Enterococcus has been largely disputed. Several studies support the finding that related isolates arise from hospital settings resulting in a high incidence of nosocomial infections.2-5 Other studies support environmental sources, including animals, as the reservoir for antibiotic-resistant Enterococcus strains.6,7 This study evaluated the genotypic variability and the level of antimicrobial resistance of Enterococcus spp. recovered from wild and captive raptors presented to or housed at the University of Illinois Wildlife Medical Clinic.


Fecal cultures were obtained from 18 wild raptors [six Buteo jamaicensis (red-tailed hawk), five Falco sparverius (American kestrel), three Bubo virginianus (great horned owl), one Otus asio (Eastern screech owl), one Pandion haliaetus (osprey), one unknown (juvenile hawk)] and four captive raptor controls (one Falco sparverius, one Bubo virginianus, one Buteo jamaicensis, and one Otus asio). Enterococcus spp. were easily recovered on CNA and M agar with or without selective enrichment in Enterococcus broth. The genetic relatedness of Enterococcus isolates was evaluated by ribotyping (RiboPrinter® Qualicon, DuPont, Wilmington, DE). The antimicrobial susceptibility was evaluated using a microdilution minimal inhibitory concentration assay (Sensititre®, Trek Diag., Westlake, OH). This study also investigated the effect of therapeutic antimicrobial treatment on the resistance patterns of three raptors (two Buteo jamaicensis and one Bubo virginianus).


The Enterococcus population of the raptors was predominantly E. fecalis, and there was very little variability among the isolates. RiboPrint© results demonstrated two dominate strains of E. fecalis in wild and captive raptorial birds. The first strain (A) showed unique bands at 11 kbp and 13 kbp, and the second (B) showed unique bands at 14 and 20 kbp. These two strains were found in both captive and wild raptor species.

Wild birds with no prior history of exposure to antimicrobials were included in this study, yet resistant strains of Enterococcus were isolated from every bird. Wild raptor isolates showed similar patterns of antimicrobial resistance when compared with isolates recovered from the captive raptor controls. While the Enterococcus isolates were uniformly susceptible to Beta lactams, they were innately resistant to cephalosporins. There was substantial variability with regard to the susceptibilities for fluoroquinolones, aminoglycosides, macrolides and tetracycline.


The funding for this study was provided by the Program in Conservation, Wildlife Population Medicine, and Ecosystem Health. The authors also appreciate the cooperation of the following institutions and individuals: the University of Illinois Wildlife Medical Clinic, Derek Paul and Sarah Dietschel, and the University of Illinois Veterinary Diagnostic Laboratory, Dr. Sara Lanka PhD, Dr. Terry Miller DVM, Gregg Clabaugh, and Brandon Smith.

Literature Cited

1.  Centers for Disease Control and Prevention (www.cdc.gov)

2.  Boyce, J.M., S.M. Opal, J.W. Chow, M.J. Zervos, G. Potter-Bynoe, C.B. Sherman, M.C. Romulo, S. Fortna, and A.A. Medeiros. Outbreak of multidrug-resistant Enterococcus faecium with transferable vanB class vancomycin resistance. J. Clin. Microbiol. 1994;32:1148–1153.

3.  Chow, J.W., A. Kuritza, D.M. Shlaes, M. Green, D.F. Sahm, and M.J. Zervos. Clonal spread of vancomycin-resistant Enterococcus faecium between patients in three hospitals in two states. J. Clin. Microbiol. 1993;31:1609–1611.

4.  Coque, T.M., J.F. Tomayko, S.C. Ricke, P.C. Okhyusen, and B.E. Murray. Vancomycin-resistant enterococci from nosocomial, community, and animal sources in the United States. Antimicrob. Agents Chemother. 1996;40:2605–2609.

5.  Handwerger, S., B. Raucher, D. Altarac, J. Monka, S. Marchione, K.V. Singh, B.E. Murray, J. Wolff, and B. Walters. Nosocomial outbreak due to Enterococcus faecium highly resistant to vancomycin, penicillin and gentamicin. Clin. Infect. Dis. 1993;16:750–755.

6.  Aarestrup, F.M. Occurrence of glycopeptide resistance among Enterococcus faecium isolates from conventional and ecological poultry farms. Microbiol. Drug Res. 1995;1:255–257.

7.  Klare, I., H. Heier, H. Claus, R. Reissbrodt, and W. Witte. vanA-mediated high level glycopeptide resistance in Enterococcus faecium from animal husbandry. FEMS Microbiol. Let. 1995;125:165–172.


Speaker Information
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Judilee Marrow, BS
College of Veterinary Medicine
University of Illinois
Urbana, IL, USA

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