There is growing evidence that anthropogenic sources of antibiotics and antimicrobial-resistant bacteria can spill over into natural ecosystems, raising questions about the role wild animals play in the emergence, maintenance, and dispersal of antibiotic resistance genes. In particular, we lack an understanding of how resistance genes circulate within wild animal populations, including whether specific host characteristics, such as social associations, promote interhost transmission of these genes. In this study, we used social network analysis to explore the forces shaping population-level patterns of resistant Escherichia coli in wild giraffe (Giraffa camelopardalis) and assess the relative importance of social contact for the dissemination of resistant E. coli between giraffe. Of 195 giraffe sampled, only 5.1% harbored E. coli isolates resistant to one or more tested antibiotics. Whole-genome sequencing on a subset of resistant isolates revealed a number of acquired resistance genes with linkages to mobile genetic elements. However, we found no evidence that the spread of resistance genes among giraffe was facilitated by interhost associations. Giraffe with lower social degree were more likely to harbor resistant E. coli, but this relationship was likely driven by a correlation between an individual's social connectedness and age. Indeed, resistant E. coli was most frequently detected in socially isolated neonates, indicating that resistant E. coli may have a selective advantage in the gastrointestinal tracts of neonates compared to other age classes. Taken together, these results suggest that the maintenance of antimicrobial-resistant bacteria in wild populations may, in part, be determined by host traits and microbial competition dynamics within the host.
Bibliographical noteFunding Information:
This work was supported by the National Science Foundation (doctoral dissertation improvement grant IOS-1209338), Phoenix Zoo, Oregon Zoo, Sigma Xi, Animal Behavior Society, American Society of Mammalogists, Explorer's Club, Northeastern Wisconsin Zoo, Cleveland Metroparks Zoo, Cleveland Zoological Society, UC Davis Wildlife Health Center, and UC Davis Faculty Research Grant program. K.V. was supported by a National Science Foundation Graduate Research Fellowship during the field phase of the project, and E.A.M. was supported in part by the University of Minnesota MnDrive program. We thank Bonnie Weber and the Atwill laboratory for assistance in laboratory work and K. Gitahi of the University of Nairobi, OPC staff, and the Office of the President of the Republic of Kenya for enabling various facets of the research.
© 2018 American Society for Microbiology.
Copyright 2019 Elsevier B.V., All rights reserved.
- Antibiotic resistance
- Escherichia coli
- Social network analysis
- Transmission dynamics