Lactococcosis is a major bacterial disease impacting rainbow trout production in South Africa and Southeast Asia, particularly during the summer. This study analysed 15 bacterial isolates from affected aquaculture facilities, revealing that Lactococcus petauri (n=12) was the predominant species, rather than the traditionally recognised L. garvieae (n=3). This finding suggests a possible shift in the aetiology of lactococcosis, with potential implications for disease management. Genotypic analysis revealed that only L. garvieae isolates carried the adhesin gene (adh), which is critical for bacterial adhesion and colonisation. Most isolates possessed sortase-anchored proteins linked to iron uptake, adhesion, and stress resistance, with the LPxTG-6 subgroup unique to L. garvieae. Variations in the capsule operon, including transposase insertions, suggest ongoing horizontal gene transfer, possibly influencing immune evasion. Antimicrobial resistance (AMR) analysis identified efflux pumps ( mdtA, lsaD) conferring resistance to macrolides and lincosamides, with additional genotypic resistance to erythromycin ( mefA, msrD) and tetracyclines ( tetS, tetL). The presence of plasmid-borne tetL raises concerns about potential gene transfer and the persistence of resistance in aquaculture systems. Prophage elements were identified in several isolates, potentially contributing to virulence, and immune modulation. Although phage therapy has shown promise in experimental settings, the presence of viral defence mechanisms may raise a unique challenge. These findings highlight the importance of monitoring pathogen evolution in aquaculture systems and suggest that ongoing genomic surveillance and treatment strategies may need to be adapted to account for the emerging role of L. petauri in lactococcosis outbreaks.

Streptococcus equi subspecies equi (S. equi) is the causative organism of the upper respiratory disease of equids, strangles, characterised by pyrexia, lymphadenopathy, and mucopurulent nasal discharge. Strangles was first reported over 750 years ago and continues to be of significance in equine populations across the globe. This review discusses how S. equi has adapted, the clinical manifestation of strangles, and how clinicians and caregivers can tackle the disease in the future. S. equi evolved from the commensal, and occasionally opportunistic pathogen, Streptococcus equi subspecies zooepidemicus refining its capabilities as it became host restricted. The success of S. equi can be attributed to its ability to cause both acute and persistent infection, the latter occurring in about 10% of those infected. In this carrier state, S. equi persists in the guttural pouch without causing clinical signs, intermittently shedding into the environment, and encountering naïve animals. Insight into the S. equi genome and lifestyle has led to advances in diagnostic assays and the development of a safe and efficacious recombinant-fusion vaccine, giving clinicians and caregivers the tools to better combat this infection. Alongside rigorous biosecurity protocols and pragmatic control measures such as screening new arrivals for exposure and carrier status, these new technologies demonstrate that strangles can be an increasingly preventable infection.