INHIBITION OF LISTERIA MONOCYTOGENES BY BOVICIN HC5, A BACTERIOCIN PRODUCED BY STREPTOCOCCUS BOVIS HC5

Authors: MANTOVANI, C - CORNELL UNIVERSITY; Russell, James

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2003
Publication Date: 10/29/2003
Citation: MANTOVANI, C., RUSSELL, J.B. INHIBITION OF LISTERIA MONOCYTOGENES BY BOVICIN HC5, A BACTERIOCIN PRODUCED BY STREPTOCOCCUS BOVIS HC5. INTERNATIONAL JOURNAL OF FOOD MICROBIOLOGY. 2003. v. 89. p. 77-83.

Interpretive Summary: Dairy cattle in the United States are often fed silage, but silages can become contaminated with the bacterium Listeria monocytogenes. Listeria are pathogens than make cattle and humans sick. We previously isolated a bacterium (Streptococcus bovis HC5) that produces a very active and heat stable bacteriocin. In this paper we demonstrate that this bacteriocin can inhibit listeria and the listeria were unable to adapt significantly. Because other workers have shown that S. bovis can be used as a silage inoculant, it appears that Streptococcus bovis HC5 could have commercial application. Research on bacteriocins has the potential to improve the health and nutrition of cattle.

Technical Abstract: A bacteriocin from Streptococcus bovis HC5 (bovicin HC5) inhibited ten strains of Listeria monocytogenes that had been isolated from plant materials, soil, contaminated silage and infected cattle. Growth experiments indicated that all of the L. monocytogenes strains were inhibited by 100 AU of bovicin HC5 ml-1, and two of the strains were inhibited by only 50 AU ml-1. L. monocytogenes cultures that were transferred with sub-lethal doses (12.5 AU ml-1) could be adapted in stepwise fashion to higher doses of bovicin HC5. However, even 'adapted' cultures did not grow if 400 AU ml-1 was added. 'Adapted' cultures that were treated with 100 AU ml-1 also grew slower and had lower final optical densities than untreated controls. The effect of bovicin HC5 on L. monocytogenes was bactericidal, and the viability of the most resistant strain (CUSI-163/94) decreased 5 to 7 logs after only 2 h of exposure. L. monocytogenes cells that were incubated in MES buffer containing glucose (2 mg ml-1) had approximately 1500 nmols intracellular potassium mg protein-1 at pH values ranging from 7.0 to 5.0. Bovicin HC5 catalyzed a nearly complete efflux of potassium in 15 min but only if the pH was less than 6.0. When the pH was greater than 6.0, the cells maintained their potassium pool. Cultures that were grown in BHI (brain heart infusion) medium with 6 mg glucose ml-1 had a final pH of 4.6, and these acid 'adapted' cells were as sensitive to bovicin HC5 as those than were grown with less glucose (2 mg ml-1), additional phosphate buffer (100 mM) and had a final pH of 6.3. These results support the idea that bovicin HC5 could be effective in counteracting listeria in contaminated silages.