Effect of growth conditions on extracellular products (EPCs) of Aeromonas hydrophila

Owing to the significant role in gastrointestinal illness of A. hydrophila, frequently detected in various raw and ready-to eat foods, its pathogenetic mechanisms are particularly studied. In this paper we report the results obtained studying in vitro the effect of O2 tension and inoculum age on the extra cellular products (ECPs) of seven strains food-borne isolated and cultured at 37 degrees. The considered factors influenced markedly bacterial growth as well as ECPs production and the more notable differences were detected among 15 hours old strains let grown slowly shaking (15SH), that showed the highest bacterial yield, and 24 h old strains cultured statically (24ST), whose haemolysin and cytotoxin production was favoured. Wilcoxon test shows as, in these latter conditions, the strains needed short time to adapt the haemolysin and cytotoxin production. The oxygen tension reduction, extending the replication time, induces the bacterial metabolism toward secondary products, as verified by Spearman test applied to ECPs indexes. The increased production per cell of virulence-associated factors could be responsible of gastrointestinal disorders caused by food-borne A. hydrophila strains, even without a massive gut colonization, especially when immunocompromised individuals ingest contaminated foods.