Abstract
The history of infectious diseases raised the plague as one of the most devastating for human beings. Far too often considered an ancient disease, the frequent resurgence of the plague has led to consider it as a reemerging disease in Madagascar, Algeria, Libya, and Congo. The genetic factors associated with the pathogenicity of Yersinia pestis, the causative agent of the plague, involve the acquisition of the pPCP1 plasmid that promotes host invasion through the expression of the virulence factor Pla. The surveillance of plague foci after the 2003 outbreak in Algeria resulted in a positive detection of the specific pla gene of Y. pestis in rodents. However, the phenotypic characterization of the isolate identified a Citrobacter koseri. The comparative genomics of our sequenced C. koseri URMITE genome revealed a mosaic gene structure resulting from the lifestyle of our isolate and provided evidence for gene exchanges with different enteric bacteria. The most striking was the acquisition of a continuous 2 kb genomic fragment containing the virulence factor Pla of the Y. pestis pPCP1 plasmid; however, the subcutaneous injection of the CKU strain in mice did not produce any pathogenic effect. Our findings demonstrate that fast molecular detection of plague using solely the pla gene is unsuitable and should rather require Y. pestis gene marker combinations. We also suggest that the evolutionary force that might govern the expression of pathogenicity can occur through the acquisition of virulence genes but could also require the loss or the inactivation of resident genes such as antivirulence genes.
Highlights
Yersinia pestis is the etiologic agent of plague, a zoonotic disease that led to more than 200 million deaths throughout three pandemic waves (Achtman et al, 2004)
The spleens of 14 rodents trapped in the Oran area of Algeria (Figure S1), during the surveillance of plague foci, were screened for the Y. pestis pla gene by Polymerase Chain Reaction (PCR)-based method
The acquisition of the pFra and pPCP1 plasmids has been essential for the evolution of Y. pestis from Y. pseudotuberculosis (Rajanna et al, 2010)
Summary
Yersinia pestis is the etiologic agent of plague, a zoonotic disease that led to more than 200 million deaths throughout three pandemic waves (Achtman et al, 2004). It seems that Y. pestis has recently evolved from its ancestor Y. pseudotuberculosis, usually causing a food-borne gastroenteritis in human (Achtman et al, 2004). Despite their close genetic relationship, which reveals few Genomic Evolution of Citrobacter koseri URMITE specific genetic elements, considerable differences subsist in the pathogenicity and transmission mechanisms of Y. pestis and Y. pseudotuberculosis (Chain et al, 2004). The global threat of the Y. pestis pathogen to human health made necessary the development of rapid molecular identification methods that target specific virulence markers, including the detection of the pla gene by Polymerase Chain Reaction (PCR) in rodents (Neubauer et al, 2000; Riehm et al, 2011)
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