Table 1.

Bacterial strains and plasmids used in this study

(A) Bacterial strains
Names	Genotype, characteristics	Reference
Escherichia coli
JM109	endA1, recA1, gyrA96, thi, hsdR17 (r−k, m+k), relA1, supE44, Δ(lac-proAB), [F´ traD36, proAB, laqIqZΔM15]	Promega
Lactococcus lactis
MG1363	plasmid free derivative of NCDO712	Laboratory collection
S. aureus
Lowenstein (ATCC 49521)	clinical isolate, capsular polysaccharide CP5-positive	Laboratory collection
COL	clinical isolate, methicillin resistant	Laboratory collection
htrA 1	COL htrA 1 :: cat, CmR	[57]
htrA 2	COL htrA 2:: spc, SpcR	[57]

(B) Plasmids
Names	Characteristics	Reference
pGEMT	T-tailed PCR product Cloning vector, AmpR	Promega
pVE8124	pGEMT derivative where recombinant htrA 1r ORF is cloned htrA 1r encodes HtrA1-ΔTM-Ser255Ala-His6 protein	This work
pVE8125	pGEMT derivative where recombinant htrA 2r ORF is cloned htrA 2r encodes SPExp4-HtrA2-ΔTM-Ser619Ala-His6 protein	This work
pLB145	pWV01; CmR; expression-secretion vector where exp4 SP-nuc is cloned under the control of a lactococcal expression system, Pzit zitR exp4 SP-nuc encodes a hybrid protein between a lactococcal signal peptide (SPExp4) and the mature secreted form of the staphylococcal nuclease (NucB)	[4]
pVE8126	pLB145 derivative where htrA 1r ORF is cloned in place of nuc ORF to be fused in frame to exp4 SP exp4 SP-htrA 1r encodes a hybrid precursor leading to secreted rHtrA1 protein	This work
pVE8127	pLB145 derivative where htrA 2r ORF is cloned in place of exp4 SP -nuc ORF htrA 2r encodes a hybrid precursor leading to secreted rHtrA2 protein	This work

Amp ^R ampicillin resistant, Cm ^R chloramphenicol resistant, Spc ^R spectinomycin resistant.