Replication of Salmonella enterica Serovar Typhimurium in Human Monocyte-Derived Macrophages

Abstract

Salmonella enterica serovar Typhimurium is a common cause of food-borne gastrointestinal illness, but additionally it causes potentially fatal bacteremia in some immunocompromised patients. In mice, systemic spread and replication of the bacteria depend upon infection of and replication within macrophages, but replication in human macrophages is not widely reported or well studied. In order to assess the ability of Salmonella Typhimurium to replicate in human macrophages, we infected primary monocyte-derived macrophages (MDM) that had been differentiated under conditions known to generate different phenotypes. We found that replication in MDM depends greatly upon the phenotype of the cells, as M1-skewed macrophages did not allow replication, while M2a macrophages and macrophages differentiated with macrophage colony-stimulating factor (M-CSF) alone (termed M0) did. We describe how additional conditions that alter the macrophage phenotype or the gene expression of the bacteria affect the outcome of infection. In M0 MDM, the temporal expression of representative genes from Salmonella pathogenicity islands 1 and 2 (SPI1 and SPI2) and the importance of the PhoP/Q two-component regulatory system are similar to what has been shown in mouse macrophages. However, in contrast to mouse macrophages, where replication is SPI2 dependent, we observed early SPI2-independent replication in addition to later SPI2-dependent replication in M0 macrophages. Only SPI2-dependent replication was associated with death of the host cell at later time points. Altogether, our results reveal a very nuanced interaction between Salmonella and human macrophages.

AtypicalSalmonella entericaserovars in murine and human infection models: Is it time to reassess our approach to the study of salmonellosis?

“…S5). This is in agreement with recent studies that used flow cytometry based techniques to quantify apoptosis in macrophages infected with different Salmonella strains 27,33 .…”

“…Differentiated human monocyte cell lines (including THP-1 and U937) have been used to explore the replication of S. enterica serovars Enteritidis and Typhimurium. Few studies describing the bacterial replication in human macrophages of atypical NTS serovars have been reported despite their epidemiological importance and their contributions to clinical cases of salmonellosis 27,28 .…”

Long-term live-cell imaging reveals new roles forSalmonellaeffector proteins SseG and SteA

“…5A). There was substantial variability for preparations of BMDMs from different mice, similar to what was observed for immunocompetent human macrophages from different donors (Lathrop et al, 2015). Nevertheless, because we tracked individual cells, we could exclude from the analysis macrophages that underwent cell death or were engulfed by other macrophages during the course of the experiment, and hence, we were able to identify individual macrophages clearing bacteria.…”

Imaging flow cytometry analysis of intracellular pathogens

“…In the case of parasites, green fluorescent protein (GFP) originally purified from the jellyfish ( Aequoria victoria ) has been successfully expressed in several protozoan intracellular parasites such as Leishmania species [10–12], Trypanosoma [13–14], Enatomoeba [15], Plasmodium [16] and Toxoplasma [17], and more recently as a dual combination with other fluorescent reporters (for example with mCherry) to follow the developmental stages of T. gondii [18]. FPs have been also successfully used for deciphering pathogenesis of bacterial intracellular infection (some examples are given in [19–24]). In these cases, the FP-tag sequence is fused to the DNA sequence of a known protein-of-interest in an expression vector that is translated as a fusion protein in the bacteria.…”