Cpa, the outer membrane protease of Cronobacter sakazakii, activates plasminogen and mediates resistance to serum bactericidal activity.
Cronobacter spp. are emerging neonatal pathogens in humans, associated with outbreaks of meningitis and sepsis. To cause disease, they must survive in blood and invade the central nervous system by penetrating the blood-brain barrier. C. sakazakii BAA-894 possesses an ~131-kb plasmid (pESA3) that encodes an outer membrane protease (Cpa) that has significant identity to proteins that belong to the Pla subfamily of omptins. Members of this subfamily of proteins degrade a number of serum proteins, including circulating complement, providing protection from the complement-dependent serum killing. Moreover, proteins of the Pla subfamily can cause uncontrolled plasmin activity by converting plasminogen to plasmin and inactivating the plasmin inhibitor α2-antiplasmin (α2-AP). These reactions enhance the spread and invasion of bacteria in the host. In this study, we found that an isogenic cpa mutant showed reduced resistance to serum in comparison to its parent C. sakazakii BAA-894 strain. Overexpression of Cpa in C. sakazakii or Escherichia coli DH5α showed that Cpa proteolytically cleaved complement components C3, C3a, and C4b. Furthermore, a strain of C. sakazakii overexpressing Cpa caused a rapid activation of plasminogen and inactivation of α2-AP. These results strongly suggest that Cpa may be an important virulence factor involved in serum resistance, as well as in the spread and invasion of C. sakazakii.
Center for Food Safety and Applied Nutrition, U.S. Food and Drug Administration, Laurel, Maryland, USA. augusto.franco-mora@fda.hhs.gov
A A
AA
Franco
M H
MH
Kothary
G
G
Gopinath
K G
KG
Jarvis
C J
CJ
Grim
L
L
Hu
A R
AR
Datta
B A
BA
McCardell
B D
BD
Tall
D000595:Amino Acid Sequence; D001483:Base Sequence; D001770:Blood Bactericidal Activity / Q000276:immunology; D003165:Complement System Proteins / Q000276:immunology / Q000378:metabolism; D044083:Cronobacter sakazakii / Q000201:enzymology* / Q000276:immunology; D006801:Humans; D015151:Immunoblotting; D008969:Molecular Sequence Data; D010802:Phylogeny; D010958:Plasminogen / Q000276:immunology / Q000378:metabolism; D010960:Plasminogen Activators / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D020539:Sequence Analysis, Protein; D012697:Serine Endopeptidases / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D037521:Virulence Factors / Q000235:genetics / Q000276:immunology / Q000378:metabolism*
D037521:Virulence Factors; D010958:Plasminogen; D003165:Complement System Proteins; D010960:Plasminogen Activators; D012697:Serine Endopeptidases; C057840:omptin outer membrane protease
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