When Vibrio is not Vibrio: misidentified Aeromonas sp. associated with equine abortions and neonatal death, revealed by MALDI-TOF and 16S rRNA sequencing

A retrospective review of equine necropsies performed at the Normandy Laboratory for Animal Health, French Agency for food, environmental and occupational health and safety (1996-2022) unexpectedly reported Vibrio alginolyticus, Vibrio parahaemolyticus and Vibrio vulnificus in equine samples using API 20NE, prompting a re-evaluation of bacterial identification. Of 27 strains, 25 were cultivable, and re-examined using API 20NE, API 20E, MALDI-TOF, 16S rRNA gene sequencing and Vibrio-specific PCR assays. API 20NE confirmed the original (erroneous) identifications; all Vibrio-specific PCR assays were negative. MALDI-TOF and 16S rRNA gene sequencing reclassified 24 strains as Aeromonas sp. and one as Acinetobacter sp., with API 20E potentially reducing misidentifications in over half the cases. Most strains came from equine fetuses and neonates in Normandy (63% infectious deaths), with the number of strains increasing during 2014-2022 (n=25) compared with 1996-2004 (n=0) and 2005-2013 (n=2). These results highlight Aeromonas sp. as emerging opportunistic pathogens linked to equine abortions, stillbirths, and neonatal deaths.