TABLE 1.

Bacterial strains used and plasmids employed to construct them

Strain or plasmid	Description (reference or source)
Strains
L. lactis-elafin	Recombinant Lactococcus lactis strain expressing elafin (1)
B. longum srp+	Commensal probiotic strain Bifidobacterium longum NCC 2705 expressing serpin (2)
B. longum srp(Con)	Recombinant Bifidobacterium longum strain derived from NCC 2705 (NCC 2705 pMDY25), constitutively producing serpin (this work)
B. longum Δsrp	Genetically modified Bifidobacterium longum strain derived from NCC 2705 (NCC 9035) without serpin coding sequences (this work)
Plasmids
pJH101	Commercially available plasmid (DSMZ) initially designed for the construction of integrable plasmids in Bacillus subtilis; contains a chloramphenicol resistance gene and does not contain origin of replication for either Bacillus subtilis or Bifidobacterium longum
pMDY24	Plasmid derived from pJH101 containing upstream and downstream sequences of the BL108 serpin gene and containing chloramphenicol resistance gene (this work)
pMDY23	Versatile reporter plasmid based on Bifidobacterium longum cryptic plasmid and Escherichia coli gusA gene and containing spectinomycin resistance gene (3)
pMDY25	Plasmid derived from pMDY23 containing a constitutive promoter in front of the BL108 serpin gene (this work)