Purpose : This study determined if L. monocytogenes developed resistance to carnocyclin A and leucocin A, grown in the presence of different carbohydrates.
Methods: Carnobacterium maltaromaticum UAL307 and Leuconostoc gelidum UAL187 were used to produce carnocyclin A and leucocin A, respectively. The bacteriocins were purified using hydrophobic interaction and reverse phase high performance liquid chromatography. Minimum inhibitory concentrations (MIC) were determined for five strains of L. monocytogenes in broth and on agar. To determine the impact of sugar substrate on development of resistance, 25oC growth curves of each strain were conducted in basal media with a defined sugar substrate (glucose, sucrose, fructose, mannose, cellobiose) with the addition of carnocyclin A or leucocin A.
Results: The concentration of leucocin A that inhibited the growth of L. monocytogenes was lower than the concentration of carnocyclin A; however, there were differences between liquid- and solid-phase systems. In broth, all strains grew in the presence of 2.2 mM leucocin A; however, on agar the MIC ranged from 11.7 to 62.5 μM leucocin A, depending on the strain. The MIC for carnocyclin A in broth was 0.83 mM to >6.7 mM, whereas on agar it ranged from 2.5 mM to >10 mM, depending on the strain. Leucocin A reduced growth rates most notably when strains were grown in glucose, fructose, and cellobiose. The lag phase was not affected by the sugar substrate. Carnocyclin A reduced growth rates among all strains compared to the control for each sugar; however, significant differences were noted among strains grown in cellobiose. The lag phase was increased for all strains in the presence of carnocylcin A, independent of sugar substrate.
Significance: This research indicated that sugar substrates influenced the sensitivity of L. monocytogenes to bacteriocins, which could allow for growth in foods.