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Macrolide Resistance Was Found in 27% of Wild Boar Streptococcal Isolates in Catalonia

Two wild boars in Vallvidrera, Catalonia
Research · Disease, parasites & microbiology

A study of streptococci from livestock, wildlife and companion animals in Catalonia, Spain found macrolide resistance in 16 of 59 isolates from wild boar (Sus scrofa), corresponding to 27.1%. Wild boar provided the second-largest sample in the study after domestic pigs.

Macrolides are an important group of antibiotics, and resistance means that bacteria are less susceptible to drugs intended to inhibit them. Detecting resistance in wild-boar streptococci matters because resistance genes carried on mobile genetic elements can spread between bacteria across livestock, wildlife and shared environments.

The researchers analysed 307 streptococcal isolates collected between 2003 and 2020. Domestic pigs accounted for 155 isolates, wild boar for 59 and Pyrenean chamois for 44, with smaller numbers from cattle, sheep, dogs, cats, rabbits, dolphins, a house sparrow and a griffon vulture. Samples from wild boar and chamois came from legally hunted animals. All isolates were tested for susceptibility to erythromycin, a macrolide, and clindamycin, a lincosamide.

Resistance was much more common in domestic pigs

Resistance was much more common in domestic-pig isolates: 84.5% were resistant to macrolides and 94.8% to lincosamides, compared with 13.2% and 18.4%, respectively, when all other animal sources were pooled. Among wild animals, macrolide resistance was detected mainly in wild-boar isolates. The authors reported macrolide and/or lincosamide-resistant streptococci in 17 of 59 wild-boar isolates overall, with Streptococcus suis the main resistant species found in wild boar. They suggest that contact between wild boar, livestock and urban environments may help explain why resistance was more evident in this wildlife host than in the other wild species examined.

Resistance genes were linked to mobile elements

Whole-genome sequencing of 50 selected resistant isolates showed that several important resistance genes, including erm(B), tet(O), vga(F) and lnu(B)-lsa(E), were associated with mobile genetic elements. The erm genes encode methylases that modify the antibiotic target site and can produce the MLSB phenotype: combined resistance to macrolides, lincosamides and streptogramin B. In S. suis, erm(B) and the tetracycline-resistance gene tet(O) were especially common, while vga(F) was associated with isolates showing lincosamide resistance alone. The predominant mobile elements belonged to the Tn5252 family. These integrative elements can carry several resistance genes together and contribute to horizontal spread between streptococci. The authors conclude that mobile genetic elements are major carriers of resistance determinants and document resistant strains not only in farm animals but also in wildlife such as wild boar.

Sources and image credit

  1. López de Egea, G., González-Díaz, A., Aragón, V., Cabezón, O., Guédon, G., Berbel, D., Cadenas-Jiménez, I., Espunyes, J., Planellas, M., Domínguez, M. Á., Leblond-Bourget, N., & Ardanuy, C. (2026). Macrolide resistance determinants and their associations in streptococci from selected livestock and wildlife species from Catalonia, Northeast Spain. Microbiology Spectrum, 14, e02567-25. https://doi.org/10.1128/spectrum.02567-25Primary open-access research article published online 16 March 2026 under CC BY 4.0. Of 307 streptococcal isolates, 59 came from wild boar. Macrolide resistance was detected in 16/59 wild-boar isolates (27.1%), and the authors reported resistant streptococci in 17/59 overall. Resistance was much higher in domestic-pig isolates, and mobile genetic elements carried several major resistance determinants.

Image: Lizel (Seiko09) / Wikimedia Commons — wild boars (Sus scrofa) in Vallvidrera, Catalonia, Spain, 18 March 2016. Illustrative photograph, not animals from the study. CC BY-SA 4.0: https://creativecommons.org/licenses/by-sa/4.0/ · CC BY-SA 4.0 · Source

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