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

Abstract

The involvement of the virulence plasmid (pSTV) of Salmonella typhimurium in human salmonellosis was examined. Most of the 224 clinical strains isolated from the blood (53) and nonblood samples (171) contained a 90 kb or larger plasmid, most of which were pSTV. The rates of pSTV carriage in the isolates showed no statistically significant difference between those derived from the blood and those from other sources (87% vs. 83%; χ2=0.49, 0.1 < P < 0.9), suggesting that pSTV may not play a critical role in promoting S. typhimurium bacteremia in humans. Nine strains with representative plasmid profiles were tested for the mouse virulence. The result revealed that these clinical isolates contained all three virulent types known: the avirulent, the highly virulent when a pSTV was present, and the moderately virulent regardless of the presence or absence of pSTV. This indicated that mouse virulence of S. typhimurium did not correlate their virulence in humans. Clinical data showed that most patients with primary bacteremia had underlying immunosuppressive diseases, whereas only a few patients with secondary bacteremia had preexisting diseases (87% vs. 13%; χ2 = 22.73, P < 0.005). It is suggested that the contribution of pSTV to S. typhimurium bacteremia in humans is likely to be limited, and both the host factor and the microbial virulence determinants on the chromosome are more important than virulence plasmid in predisposing patients to bacteremia.

Salmonella Pathogenicity and Host Adaptation in Chicken-Associated Serovars

“…While our knowledge of the genetic composition of these plasmids has greatly increased with the advent of next-generation sequencing, our understanding of the evolution and dissemination of these plasmids and their interactions with one another remains limited. There is not a clear correlation between carriage of the plasmid and the establishment of systemic disease in humans, further suggesting that it may be a requirement of some strains but not others (401).…”

In Vivo Acquisition of Ceftriaxone Resistance in Salmonella enterica Serotype Anatum

“…The transformant was used as the donor in the subsequent conjugation experiment. Bacterial conjugation was performed as described earlier (6), except that S. enterica serotype Typhimurium LBNP4417 (Nal r Str r ) was used as the recipient. Transconjugants were selected on MacConkey agar medium containing appropriate drugs (ceftriaxone, streptomycin, and nalidixic acid).…”

The Importance of Mobile Genetic Elements in the Evolution of Salmonella: Pathogenesis, Antibiotic Resistance and Host Adaptation

“…Whether the virulence plasmid is necessary to produce systemic infections in humans has been subject of intense debate. Some authors claim that there is lack of evidence of an association between the carriage of the virulence plasmid and human bacteremia (Chiu et al, 2000). Other authors suggest that spv genes promote the dissemination of Typhimurium from the intestine (Fierer 2001).…”

“…Despite many common properties shared by these plasmids, each virulence plasmid seems to be specific to its serovar, but the outcome of the infection in different animal hosts may be variable. For example, Typhimurium strains that harbour the virulence plasmid are highly virulent to mouse, but there is lack of evidence of an association between the carriage of virulence plasmid and the bacteremia caused in humans (Chiu et al, 2000). Whether the virulence plasmid is necessary to produce systemic infections in humans has been subject of intense debate.…”

“…Eight Salmonella enterica serovars harbour a large (50-285 kb) plasmid named the Salmonella virulence plasmid, containing the spv operon, which is a major determinant of virulence in their specific hosts (Gulig et al, 1993;Chiu et al, 2000;Fierer and Guiney 2001). In addition to the spv operon, other plasmid genes are involved in virulence.…”