European mecC-MRSA lineages arose during the modern antibiotic era because medical or veterinary antibiotic use selected for methicillin resistance.

MRSA stands for methicillin-resistant Staphylococcus aureus: strains of a common bacterium that can resist methicillin and related antibiotics. One way MRSA can acquire that resistance is through a gene called mecC.

When mecC-MRSA was found in livestock and people in the early 2010s, modern antibiotic use seemed like the obvious explanation. Medicine and agriculture create strong selection for bacteria that can survive antibiotics.

European hedgehogs complicated that story. They carried closely related mecC-MRSA at unusually high rates. Comparisons of bacterial genomes indicated that major lineages had begun diversifying roughly 130–200 years ago, before methicillin and the modern clinical antibiotic era.

Researchers then found a plausible source of natural antibiotic pressure on the hedgehogs themselves. A fungus associated with hedgehog skin, Trichophyton erinacei, produces β-lactam antibiotics. In that environment, susceptible S. aureus can be inhibited while resistant strains have an advantage.

Human antibiotic use still drives many resistance problems and can spread resistant bacteria. The correction here is more specific: these mecC-MRSA lineages did not need modern medicine to create the resistance in the first place.