Use of autocytotoxic β-D-galactosides for selective growth of Salmonella typhimurium in the presence of coliforms

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Abstract
Selective inhibition of lactose-fermenting coliforms in the presence of Salmonella typhimurium was obtained by growing the mixed culture in media containing certain synthetic β-D-galactosides. The inhibition resulted from autocytotoxicity affecting the coliforms but not S. typhimurium, and occurred with phenyl-(PG), phenethyl-(PEG), and 4-chloro-2-cyclopentylphenyl-(CPPG) β-D-galactosides. Strains of coliforms which were capable of undergoing autocytotoxicity yielded cell-free extracts that hydrolyzed PEG and CPPG, and these extracts also hydrolyzed the galactosidase assay compound, o-nitrophenyl β-D-galactoside (ONPG).They did not, however, hydrolyze o-nitrophenyl β-D-galactoside-6-phosphate (ONPG-6-PO4).A few strains of Enterobacter aerogenes and Klebsiella pneumoniae, although they fermented lactose, were not subject to autocytotoxicity. Cell-free extracts of these strains did not hydrolyze PEG, CPPG, or ONPG. They did, however, hydrolyze ONPG-6-PO4. In this respect, their galactosidase system resembles that of Staphylococcus aureus: extracts of S. aureus hydrolyze ONPG-6-PO4, but not ONPG.

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