The virulence of Salmonella Enteritidis in Galleria mellonella is improved by N-dodecanoyl-homoserine lactone.

ABSTRACT

Salmonella is a food and waterborne pathogen responsible for outbreaks worldwide, and it can survive during passage through the stomach and inside host phagocytic cells. Virulence genes are required for infection and survival in macrophages, and some are under the regulation of the quorum sensing (QS) system. This study investigated the influence of the autoinducer 1 (AI-1), N-dodecanoyl-homoserine lactone (C12-HSL), on the virulence of Salmonella PT4 using Galleria mellonella as an infection model. Salmonella PT4 was grown in the presence and absence of C12-HSL under anaerobic conditions for 7 h, and the expression of rpoS, arcA, arcB, and invA genes was evaluated. After the inoculation of G. mellonella with the median lethal dose (LD50) of Salmonella PT4, the survival of bacteria inside the larvae and their health status (health index scoring) were monitored, as well as the pigment, nitric oxide (NO), superoxide dismutase (SOD), and catalase (CAT) production. Also, the hemocyte viability, the induction of caspase-3, and microtubule-associated light chain 3 (LC3) protein in hemocytes were evaluated. Salmonella PT4 growing in the presence of C12-HSL showed increased rpoS, arcA, arcB, and invA expression and promoted higher larvae mortality and worse state of health after 24 h of infection. The C12-HSL also increased the persistence of Salmonella PT4 in the hemolymph and in the hemocytes. The highest pigmentation, NO production, and antioxidant enzymes were verified in the larva hemolymph infected with Salmonella PT4 grown with C12-HSL. Hemocytes from larvae infected with Salmonella PT4 grown with C12-HSL showed lower viability and higher production of caspase-3 and LC3. Taken together, these findings suggest that C12-HSL could be involved in the virulence of Salmonella PT4.