Val-Calvo, J. | Search bioRxiv

bioRxiv2025

Multidrug-resistant Rhodococcus equi (MDR-RE): detection in East Asia confirms global spread

Macrolide (multidrug)-resistant Rhodococcus equi (MDR-RE) emerged in the early 2000s and has since been disseminating across equine farms in the United States. In 2016, it was found in Ireland, presumably introduced through horse imports. Here, we report its identification in Japan, together with evidence of its presence in China. A recent isolate from Ireland suggests ongoing importation events. These findings highlight the continued international spread of MDR-RE and its potential to become globally established. Currently circulating among horses, MDR-RE is likely to arise in humans over time. Active surveillance is essential to monitor and control this emerging zoonotic antimicrobial resistance threat worldwide.

microbiology↗

bioRxiv2025

Leveraging the subgenus category to address genus over-splitting exemplified with Prescottella and other recently proposed Mycobacteriales genera.

Three related circumstances are compromising the stability of prokaryotic taxonomy and nomenclature, with a significant impact in the field of pathogenic microorganisms: (i) the growing trend of subdividing existing genera by arbitrary phylogenomics-based demarcations, creating an increasing number of new genera; (ii) the priority of databases towards the last validly published names; and (iii) the irreversibility of new names in databases even if changes in taxonomic opinion support reverting to previous classifications. Given the understandable end-user reluctance to name changes affecting well-known pathogens, parallel nomenclatures coexist, creating confusion. Here, we address this problem by exploiting the subgenus category to form new combinations that can be adopted by databases as per their latest validly published name priority policy. The proposed approach consists in lowering to subgenus rank the new genera arising from genus splits considered to be unwarranted. According to the Prokaryotic Code, the species in question would be designated with their previous generic synonym and, in parentheses, the subgenus name (which would correspond to the latest synonym used by the databases). Being the subgenus an optional taxonomic category, it can be omitted, but its use may facilitate the mapping of the synonyms in databases and the literature. For illustration, we apply the strategy to recent genus splits in the Mycobacteriales, specifically the new nested genus Prescottella within the rhodococcal radiation and the several new genera into which Mycobacterium was subdivided.

microbiology↗

bioRxiv2022

International spread of emerging multidrug-resistant Rhodococcus equi

The recently characterized multidrug-resistant clone of the animal and human zoonotic pathogen Rhodococcus equi, MDR-RE 2287, has been circulating among horse farms in the United States (US) since the early 2000s. Here, we report the first documented detection of the MDR-RE 2287 clone outside the US. The finding highlights the risk of MDR-RE spreading internationally with the movement of horses.

microbiology↗