TABLE 1.

Bacterial strains and plasmids used in this study

Strain or plasmidGenotype or characteristicsReference or source
L. acidophilus strains
    NCFMHuman intestinal isolate 8
    NCK1392NCFM harboring pTRK669 46
    NCK1909NCFM carrying a 315-bp in-frame deletion in the upp geneThis study
    NCK1910NCK1909 harboring pTRK669; host for pORI-based counterselective integration vectorThis study
    NCK1962NCK1909 carrying a 1,356-bp in-frame deletion in the slpX geneThis study
E. coli strains
    EC101RepA+ JM101; Kmr; repA from pWV01 integrated in chromosome; host for pORI-based plasmids 34
    NCK1391 E. coli DH10B harboring pTRK669; host for pORI-based plasmidsW. M. Russell and T. R. Klaenhammer, unpublished data
Plasmids
    pORI28Emr Ori+ (pWV01), replicates only with repA provided in trans 34
    pORI19 lacZ′ derivative of pORI28 34
    pTRK669Ori (pWV01), Cmr RepA+ 46
    pTRK9343.4 kb; pORI19 with a mutated copy of upp cloned into XbaI/SacI sitesThis study
    pTRK9353.0 kb; pORI28 with a upp expression cassette and lacZ′ from pUC19 cloned into BglII/XbaI sites; serves as counterselective integration vectorThis study
    pTRK9564.5 kb; pTRK935 with a mutated copy of slpX cloned into BamHI/SacI sitesThis study