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Keywords:

  • Brucella melitensis ;
  • cold shock protein (CSP);
  • stress resistance;
  • virulence

Abstract

Brucella melitensis is a facultative intracellular pathogen that mainly resides within macrophages. The mechanisms employed by Brucella to adapt to harsh intracellular environments and survive within host macrophages are not clearly understood. Here, we constructed a cspA gene deletion mutant, NIΔcspA, that did not exhibit any discernible growth defect at a normal culture temperature (37 °C) or at a low temperature (15 °C). However, expression of the cspA gene in Brucella was induced by cold, acidic, and oxidative conditions, as determined via quantitative reverse transcription PCR. Unlike its parental strain, B. melitensis NI, the NIΔcspA mutant showed an increased sensitivity to acidic and H2O2 stresses, especially during the mid-log-phase, and these stress conditions would presumably be encountered by bacteria during intracellular infections. Moreover, macrophage and mouse infection assays indicated that the NIΔcspA mutant fails to replicate in cultured J774.A1 murine macrophages and is rapidly cleared from the spleens of experimentally infected BALB/c mice. These findings suggest that the Brucella cspA gene makes an essential contribution to virulence in vitro and in vivo, most likely by allowing brucellae to adapt appropriately to the harsh environmental conditions encountered within host macrophages.