Protease production by Burkholderia pseudomallei and virulence in mice

Unité de Microbiologie, Centre de Recherche du Service de Santé des Armées Emile Pardé, La Tronche, France.
Acta Tropica (Impact Factor: 2.27). 03/2000; 74(2-3):215-20. DOI: 10.1016/S0001-706X(99)00073-X
Source: PubMed


The aim of this study was to assess protease production and virulence of various Burkholderia pseudomallei strains. Protease activity was evaluated in filtrates from cultures grown for 50 h in TSB Dialysate by azocasein hydrolysis, and expressed as absorbancy at 405 nm. Virulence was assessed in 8 weeks old SWISS mice, by intraperitoneal injection of 6-6 x 10(5) CFU, and the LD50 was calculated after 30 days by the method of Reed and Muench. The lethal activity was studied for five strains of B. pseudomallei and the type strains of Burkholderia pseudomallei, Burkholderia mallei, and Burkholderia cepacia. The three type strains appeared to be low protease producers (A405 = 0.11, 0.09 and 0.00, respectively) and avirulent. The two more virulent B. pseudomallei strains exhibited significantly different LD50, 3.5 x 10(2) (IPP 6068 VIR) versus 2.1 x 10(5) CFU/mouse (40/97), and protease activities (A405 = 0.046 and 0.79, respectively). Moreover, the avirulent parent of IPP 6068 (AG), was a better protease producer than the 6068 VIR strain, A405 = 0.26 versus 0.046. These results suggest that there is no correlation between virulence and level of exoproteolytic activity, when B. pseudomallei is injected to mice via the intraperitoneal route.

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    • "Secretion of protease, lipase and phospholipase occurs via the type II general secretory pathway (Gsp); gsp mutants lack secretion, but are not attenuated for virulence in hamsters (DeShazer et al., 1999). Furthermore, no correlation has been observed between protease production in six B. pseudomallei strains and virulence in BALB/c mice (Gauthier et al., 2000). These data suggest that the exoproducts, including protease, lipase and phospholipase play, at most, a minor role in virulence. "
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    ABSTRACT: Melioidosis, a febrile illness with disease states ranging from acute pneumonia or septicaemia to chronic abscesses, was first documented by Whitmore & Krishnaswami (1912). The causative agent, Burkholderia pseudomallei, was subsequently identified as a motile, gram-negative bacillus, which is principally an environmental saprophyte. Melioidosis has become an increasingly important disease in endemic areas such as northern Thailand and Australia (Currie et al., 2000). This health burden, plus the classification of B. pseudomallei as a category B biological agent (Rotz et al., 2002), has resulted in an escalation of research interest. This review focuses on the molecular and cellular basis of pathogenesis in melioidosis, with a comprehensive overview of the current knowledge on how B. pseudomallei can cause disease. The process of B. pseudomallei movement from the environmental reservoir to attachment and invasion of epithelial and macrophage cells and the subsequent intracellular survival and spread is outlined. Furthermore, the diverse assortment of virulence factors that allow B. pseudomallei to become an effective opportunistic pathogen, as well as to avoid or subvert the host immune response, is discussed. With the recent increase in genomic and molecular studies, the current understanding of the infection process of melioidosis has increased substantially, yet, much still remains to be elucidated.
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    • "The pathogenesis of B. pseudomallei infections involves the expression of cell-associated components such as lipopolysaccharide, pili, extracellular polysaccharide, and flagella [3] as well as secreted factors including toxins [11], protease [12], siderophore [13] and phospholipase [14]. Although capsular polysaccharide has been shown to enhance the intracellular survival and virulence of the pathogen, the role of this and other factors in pathogenicity and host resistance has not been conclusively resolved [15-17]. "
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    • "An overnight shaken bacterial culture in Brain Heart Infusion broth at 37³C (Difco Laboratories) was centrifuged, washed twice, and serially diluted in sterile saline at physiological pH to the desired concentration. The infective dose for an acute infection was based on previous experimentation [37] "
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