Avian Salmonella enteritidis serovar Enteritidis with ClpP deletion is attenuated and highly immunogenic in chickens

Abstract

Salmonella enterica subsp. enterica serovars are leading causative agents of gastroenteritis in humans and numerous animalspecies worldwide. The ClpP from Salmonella enterica is responsible for regulation under various stress conditions. We were interested inthe effect of ClpP deletion mutation on attenuation of Salmonella enterica subsp. enterica serovar Enteritidis (SE) in chickens. Therefore,SM-6/ΔClpP, deletion of the ClpP gene from a wild-type SE-6 (SM-6) strain, was generated using the phage λ Red homologousrecombination. Compared with SM-6, SM-6/ΔClpP represented a retarded growth rate and lower concentration in LB broth with andwithout 5% NaCl or lower pH values, indicating that it is sensitive to conventional disinfectants. SM-6/ΔClpP represented reducedinvasion into macrophages in vitro and an approximate 400-fold attenuation based on cell invasion assay and median lethal dose (LD50)in specific pathogen-free (SPF) chickens. Furthermore, SM-6/ΔClpP showed reduced colonization in the liver and spleen and fasterclearance compared with SM-6, indicating a short discharge. The survival rate of 7-day-old SPF chickens immunized with SM-6/ΔClpPagainst homologous challenge and antibody kinetics indicated that SM-6/ΔClpP provided efficient protection from lethal challenge andinduced robust antibody immune responses, demonstrating the potential of live, attenuated SE as a vaccine candidate.