Intracellular Salmonella typhimurium Induce Lysis of Human Polymorphonuclear Leukocytes Which Is Not Associated with the Salmonella Virulence Plasmid

Abstract

The interaction between Salmonella typhimurium and human polymorphonuclear leukocytes (PMNs) was analyzed in vitro. Three S. typhimurium strains, the wild-type strain OU5043, its isogenic virulence plasmid-cured strain OU5048, and LT2, which represented the types that exhibited three mouse virulence levels, respectively, were used in this study. There was no correlation between the recovery of intracellular S. typhimurium from PMNs and the presence or absence of the virulence plasmid, or the strains' mouse virulence level. When the oxygen-dependent response of PMNs upon phagocytosis of S. typhimurium was examined by checking the intracellular reduction of nitroblue tetrazolium (NBT), the fraction of PMNs that reduced NBT on phagocytosis of the three strains was around 80 %, whereas it was 58 % with Escherichia coli, 95 % with phorbol 12-myristate 13-acetate and 15 % with a negative control. Thus there were no significant differences among the three Salmonella strains in terms of their ability to induce the oxidative response in PMNs. Microscopic analysis of Salmonella-infected PMNs indicated that the intracellular Salmonella induced lysis of PMNs. Both OU5043 and OU5048 exhibited a significant intracellular cytotoxic effect on PMNs after 24 hr of infection and this effect was not associated with the presence or absence of the virulence plasmid. On the other hand, lysis of PMNs was related to the intracellular survival of Salmonella, as ofloxacin, an antibiotic, appeared to be able to protect human PMNs from Salmonellainduced cytotoxicity when this agent was added into the medium to inactivate the intracellular organism. The ability to induce lysis of PMNs by either wild-type or plasmid-cured strains of S. typhimurium may play a crucial role in the pathogenesis of non-typhoid Salmonella. The contribution of pSTV to humam salmonellosis is likely to be limited. Furthermore, early institution of antibiotics with a high intracellular activity against Salmonella, such as fluoroquinolones, may be useful to prevent the dissemination of Salmonella infection.

Lack of Evidence of an Association between the Carriage of Virulence Plasmid and the Bacteremia of Salmonella typhimurium in Humans

“…In the past several years, there have been no further studies examining this specific issue, and supportive evidence appears lacking. In an earlier in vitro study, we found that either pSTV-carrying or isogenic plasmidless S. typhimurium can evade the killing by human leukocytes, and that the presence or absence of pSTV does not influence the intracellular survival of S. typhimurium in leukocytes (4). Similar results were also reported by other investigators (24).…”

Analysis of Cells Targeted by Salmonella Type III Secretion In Vivo

“…However, depletion studies based on anti-GR-1 deplete not only neutrophils but also monocytes, consequently it is difficult to assess the role of neutrophils [ 22 , 35 , 43 ]. In vitro, neutrophils kill Salmonella only in the first two hours followed by intracellular bacterial replication [ 44 – 46 ] precisely the same pattern as observed for primary macrophages [ 47 – 50 ].…”

Prevalence of the Virulence Plasmids of Nontyphoid Salmonella in the Serovars Isolated from Humans and Their Association with Bacteremia

“…Humans can also be infected by most of these serovars but are not the natural hosts of any of them. On the basis of data from this and other animal and molecular epidemiological studies (1,2,5,8), it could be concluded that chromosomal virulence genes, rather than the virulence plasmid, are the most important microbial determinants responsible for the virulence phenotype of nontyphoid Salmonella in humans. What role virulence plasmids play in human infections is still not fully understood; nevertheless, in S. choleraesuis, S. dublin, and S. enteritidis, the plasmids seemed to be required for primary bacteremia caused by these serovars to occur.…”