Survival capacity of the common woodlouse Armadillidium vulgare is improved with a second infection of Salmonella enterica

Abstract

Immune priming has been widely observed in invertebrates. However, this phenomenon remains incompletely characterized concerning the time course of the protective effect and immune responses. Here, we investigated the existence of a protective effect in the terrestrial isopod Armadillidium vulgare against a second infection with the bacterium Salmonella enterica. We primed animals with a low dose of living bacteria or with the bacterial culture medium. One day, 7 or 15 days later, we measured haemocytes concentration and viability and we injected a LD50 of living S. enterica to monitor the survival rates of infected individuals. We show that A. vulgare is better protected (i.e. survival improvement) upon secondary infection when it has encountered S. enterica 7 days before. This protection, which tends to persist 15 days after the first infection, is however not observed when the priming is performed only 1 day before the LD50 injection. Besides providing a new invertebrate example, we highlight this protection is dynamic and may be partly due to a high haemocyte production.

Immune priming depends on age, sex and Wolbachia in the interaction between Armadillidium vulgare and Salmonella

“…Cultures of S. enterica were produced as described in Prigot‐Maurice et al. (2019). In short, we performed the bacterial cultures from a frozen glycerol stock dropped in Luria‐Bertani (LB) broth, composed of 25 g/L of LB base (Invitrogen 12795‐027) and eventually supplemented with 15 g/L of agar‐agar (Fisher BioReagentsTM BP1423‐2) to spread bacteria onto LB agar plates.…”

“…To perform our experiment, we used the pathogenic bacterium Salmonella enterica serovar Typhimurium J18 (Verdon et al., 2016), already known to induce immune priming in A. vulgare (Prigot‐Maurice et al., 2019) . S. enterica is a gram‐negative and facultative intracellular bacterium, with the same structure and ecological niche as Wolbachia .…”

“…We isolated individuals of the same group and priming treatment per 5 in plastic boxes (5 cm × 8 cm Ø) containing a moist paper, under a natural photoperiod at 20°C. Seven days later, non‐primed, LB‐primed and S. enterica ‐primed individuals were all injected with a LD 50 (dosage killing 50% of individuals in 7 days) of 3.10 6 ± 1.10 6 living S. enterica in 100 nl (Braquart‐Varnier et al., 2015; Prigot‐Maurice et al., 2019). The injected dose was controlled as for the priming treatment.…”

“…Wolbachia is detectable in most animal tissues, including haematopoietic organs and haemocytes (Braquart‐Varnier et al., 2015), where it induces the over‐expression of immune genes and a decline in immune functions in older individuals (Chevalier et al., 2011, 2012; Sicard et al., 2010). In addition, A. vulgare can mount an immune priming protection against S. enterica (Prigot‐Maurice et al., 2019). A first infection occurring 7 days before a second sub‐lethal infection improves survival rates of primed individuals and increases persistently their haemocyte viabilities (Prigot‐Maurice et al., 2019).…”

“…In addition, A. vulgare can mount an immune priming protection against S. enterica (Prigot‐Maurice et al., 2019). A first infection occurring 7 days before a second sub‐lethal infection improves survival rates of primed individuals and increases persistently their haemocyte viabilities (Prigot‐Maurice et al., 2019).…”