Genomic analysis of Aeromonas species isolated from retail foods suggests an under-investigated population

Abstract

The genus Aeromonas includes species capable of causing disease in a range of hosts, including humans. With some species implicated in outbreaks of illness, these bacteria are considered emerging foodborne pathogens. This study examined Aeromonas isolates contaminating UK retail food samples, and characterised the population structure and relevance to public health. Six Aeromonas species were identified: A. media, A. rivipollensis, A. salmonicida, and A. veronii, in addition to two putative previously undescribed Aeromonas species. Phylogenetic comparisons showed a diverse population, with 25 multi locus sequence types (STs) identified (23 of which were novel STs), and no clonal complexes observed. Chromosomal β-lactamase genes carriage was common across all isolates, including carbapenemase and AmpC-like resistance markers. In addition, mobile genetic elements and genomic islands harbouring resistant markers to antibiotics and heavy metals were widespread, including a class I integron-associated floR amphenicol-resistance marker. A. media formed greater biofilm biomass than A. salmonicida or A. veronii. In G. mellonella infection models, A. veronii, A. media, and an unknown Aeromonas species demonstrated the highest virulence (100 % mortality), while A. rivipollensis-infected larvae displayed the highest survival rates (43 % survival). This study provides new insights into the potential food safety relevance of Aeromonas species in retail foods, and highlights an association with horticulture products. Collectively, the results of this study demonstrate a knowledge gap on the food product-associated Aeromonas population, which should be afforded further study to ensure a robust appreciation of food safety significance, and public health perspectives.