|Kariyawasam, Subhashinie - Pennsylvania State University|
|Borst, Luke - North Carolina State University|
Submitted to: Letters in Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/2014
Publication Date: 2/1/2015
Citation: Jackson, C.R., Kariyawasam, S., Borst, L.B., Frye, J.G., Barrett, J.B., Hiott, L.M., Woodley, T.A. 2015. Antimicrobial resistance, virulence determinants, and genetic profiles of clinical and nonclinical Enterococcus cecorum from poultry. Letters in Applied Microbiology. 60(2):111-119.
Interpretive Summary: Enterococcus cecorum is a Gram-positive bacterium that causes a number of diseases in poultry. The characteristics that contribute to pathogenesis of E. cecorum in poultry have not been defined. In this study, antimicrobial resistance phenotype, presence of virulence determinants, and genetic relatedness of E. cecorum from clinical poultry cases and poultry carcass rinsates (non-clinical) was determined. The majority of isolates from both groups was multidrug resistant and harbored few virulence determinants. Using Pulsed-Field Gel Electrophoreses, isolates mostly grouped by source although some clinical isolates were present among those from carcass rinsates. Results from this study suggest that clinical E. cecorum and E. cecorum from poultry carcass rinsates may share a common genetic background; clinical E. cecorum possess virulence determinants that have not been previously described for the enterococci. Elucidation of those unknown virulence determinants is important for determination of the pathogenesis of E. cecorum infections in poultry and for production of a vaccine candidate for protection of poultry flocks. This research is useful for veterinarians who treat poultry for infections caused by E. cecorum and for researchers who study diseases of poultry.
Technical Abstract: Although enterococci are considered commensal bacteria, they are capable of causing disease in humans and animals. Enterococcus cecorum has been implicated as a possible cause of disease in poultry across the world. However, the characteristics that contribute to pathogenesis of E. cecorum in poultry have not been defined. In order to determine if clinical E. cecorum differ from isolates from E. cecorum from non-diseased poultry, E. cecorum from both groups were compared based upon antimicrobial resistance phenotype, presence of virulence determinants, and genetic relatedness using Pulsed-Field Gel Electrophoresis (PFGE). A total of 105 E. cecorum were isolated from poultry carcass rinsates (n=75) and diseased broilers and broiler breeders (n=30). Of the 16 antimicrobials tested, E. cecorum from carcass rinsates were resistant to ten of the antimicrobials while clinical E. cecorum were resistant to six (erythromycin, kanamycin, lincomycin, streptomycin, tetracycline, and tylosin). The majority of E. cecorum from carcass rinsates was resistant to lincomycin (54/75; 72%) followed by tetracycline (46/75; 61.3%) while the highest level of resistance among clinical E. cecorum was to tetracycline (22/30; 73.3%) and erythromycin (11/30; 36.7%). Multi-drug resistance (MDR; resistance to 2 or more antimicrobials) was identified in E. cecorum from carcass rinsates (53/75; 70.7%) and diseased poultry (18/30; 60%). Twenty-one MDR patterns were present among the carcass rinse isolates and eight patterns for E. cecorum from diseased birds. Of the virulence determinants tested, efaAfm was present in almost all of the isolates tested (104/105; 99%); agg was detected in two carcass rinsate E. cecorum while another carcass rinsate isolate contained cad, ccf, cob, cpd, cylA, cylB, cylM, efaAfs, and gelE. Using PFGE, the majority of clinical isolates clustered together; however a few clinical isolates grouped with E. cecorum from carcass rinsates. Taken together, this data suggests that distinguishing the two groups of isolates is difficult based upon the characterization criteria used as antimicrobial resistance was common in both clinical and non-clinical E. cecorum and a majority of E. cecorum from both groups lack previously described enterococcal virulence determinants. Results of genetic analysis also suggests that clinical E. cecorum may have been derived from a non-pathogenic precursor and the use of molecular genetic methods may not be effective in distinguishing the two groups. Additional studies are needed to determine virulence determinants present in clinical E. cecorum which enable them to infect and cause disease in poultry.