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Matuszewska M, Dabrowska A, Murray GGR, Kett SM, Vick AJA, Banister SC, Pantoja Munoz L, Cunningham P, Welch JJ, Holmes MA, Weinert LA. Absence of Staphylococcus aureus in Wild Populations of Fish Supports a Spillover Hypothesis. Microbiol Spectr 2023; 11:e0485822. [PMID: 37341608 PMCID: PMC10434045 DOI: 10.1128/spectrum.04858-22] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2022] [Accepted: 05/23/2023] [Indexed: 06/22/2023] Open
Abstract
Staphylococcus aureus is a human commensal and opportunistic pathogen that also infects other animals. In humans and livestock, where S. aureus is most studied, strains are specialized for different host species. Recent studies have also found S. aureus in diverse wild animals. However, it remains unclear whether these isolates are also specialized for their hosts or whether their presence is due to repeated spillovers from source populations. This study focuses on S. aureus in fish, testing the spillover hypothesis in two ways. First, we examined 12 S. aureus isolates obtained from the internal and external organs of a farmed fish. While all isolates were from clonal complex 45, genomic diversity indicates repeated acquisition. The presence of a φSa3 prophage containing human immune evasion genes suggests that the source was originally human. Second, we tested for S. aureus in wild fish that were isolated from likely sources. In particular, we sampled 123 brown trout and their environment at 16 sites in the remote Scottish Highlands with variable levels of exposure to humans, birds, and livestock. This screen found no S. aureus infection in any of the wild populations or their environment. Together, these results support that the presence of S. aureus in fish and aquaculture is due to spillover from humans rather than specialization. Given the trends of increasing fish consumption, a better understanding of the dynamics of S. aureus spillover in aquaculture will mitigate future risks to fish and human health. IMPORTANCE Staphylococcus aureus is a human and livestock commensal but also an important pathogen responsible for high human mortality rates and economic losses in farming. Recent studies show that S. aureus is common in wild animals, including fish. However, we do not know whether these animals are part of the normal host range of S. aureus or whether infection is due to repeated spillover events from true S. aureus hosts. Answering this question has implications for public health and conservation. We find support for the spillover hypothesis by combining genome sequencing of S. aureus isolates from farmed fish and screens for S. aureus in isolated wild populations. The results imply that fish are unlikely to be a source of novel emergent S. aureus strains but highlight the prominence of the spillover of antibiotic-resistant bacteria from humans and livestock. This may affect both future fish disease potential and the risk of human food poisoning.
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Affiliation(s)
- Marta Matuszewska
- Department of Veterinary Medicine, University of Cambridge, Cambridge, United Kingdom
- Department of Medicine, University of Cambridge, Cambridge, United Kingdom
| | - Alicja Dabrowska
- Department of Veterinary Medicine, University of Cambridge, Cambridge, United Kingdom
- Department of Physics, University of Cambridge, Cambridge, United Kingdom
| | - Gemma G. R. Murray
- Department of Veterinary Medicine, University of Cambridge, Cambridge, United Kingdom
- Department of Genetics, Evolution and Environment, University College London, London
| | - Steve M. Kett
- Department of Natural Sciences, Middlesex University London, London, United Kingdom
| | - Andy J. A. Vick
- RAL Space (UKRI-STFC), Harwell Campus, Didcot, Oxfordshire, United Kingdom
| | - Sofie C. Banister
- School of History, Classics and Archaeology, University of Edinburgh, Edinburgh, United Kingdom
| | | | - Peter Cunningham
- Wester Ross Fisheries Trust, Harbour Centre, Gairloch, Wester Ross, United Kingdom
| | - John J. Welch
- Department of Genetics, University of Cambridge, Cambridge, United Kingdom
| | - Mark A. Holmes
- Department of Veterinary Medicine, University of Cambridge, Cambridge, United Kingdom
| | - Lucy A. Weinert
- Department of Veterinary Medicine, University of Cambridge, Cambridge, United Kingdom
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