AUTHOR=Bhowmik Bijit K. , Kumar Arvind , Gangaiah Dharanesh 

TITLE=Transcriptome Analyses of Chicken Primary Macrophages Infected With Attenuated Salmonella Typhimurium Mutants

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.857378

DOI=10.3389/fmicb.2022.857378

ISSN=1664-302X

ABSTRACT=<p><italic>Salmonella enterica</italic> is one of the most common foodborne illnesses in the United States and worldwide, with nearly one-third of the cases attributed to contaminated eggs and poultry products. Vaccination has proven to be an effective strategy to reduce <italic>Salmonella</italic> load in poultry. The <italic>Salmonella</italic> Typhimurium Δ<italic>crp</italic>-<italic>cya</italic> (MeganVac1) strain is the most commonly used vaccine in the United States; however, the mechanisms of virulence attenuation and host response to this vaccine strain are poorly understood. Here, we profiled the invasion and intracellular survival phenotypes of Δ<italic>crp</italic>-<italic>cya</italic> and its derivatives (lacking key genes required for intra-macrophage survival) in HD11 macrophages and the transcriptome response in primary chicken macrophages using RNA-seq. Compared to the parent strain UK1, all the mutant strains were highly defective in metabolizing carbon sources related to the TCA cycle and had greater doubling times in macrophage-simulating conditions. Compared to UK1, the majority of the mutants were attenuated for invasion and intra-macrophage survival. Compared to Δ<italic>crp</italic>-<italic>cya</italic>, while derivatives lacking <italic>phoPQ, ompR-envZ, feoABC</italic> and <italic>sifA</italic> were highly attenuated for invasion and intracellular survival within macrophages, derivatives lacking <italic>ssrAB, SPI13, SPI2, mgtRBC, sitABCD, sopF, sseJ</italic> and <italic>sspH2</italic> showed increased ability to invade and survive within macrophages. Transcriptome analyses of macrophages infected with UK1, Δ<italic>crp</italic>-<italic>cya</italic> and its derivatives lacking <italic>phoPQ, sifA</italic> and <italic>sopF</italic> demonstrated that, compared to uninfected macrophages, 138, 148, 153, 155 and 142 genes were differentially expressed in these strains, respectively. Similar changes in gene expression were observed in macrophages infected with these strains; the upregulated genes belonged to innate immune response and host defense and the downregulated genes belonged to various metabolic pathways. Together, these data provide novel insights on the relative phenotypes and early response of macrophages to the vaccine strain and its derivatives. The Δ<italic>crp</italic>-<italic>cya</italic> derivatives could facilitate development of next-generation vaccines with improved safety.</p>