Studies with bioengineered Nisin peptides highlight the broad-spectrum potency of Nisin V.
Bottom Line: In contrast, Nisin V displayed increased potency against all targets tested including hVISA strains and the hyper-virulent Clostridium difficile ribotype 027 and against important food pathogens such as Listeria monocytogenes and Bacillus cereus.Significantly, this enhanced activity was validated in a model food system against L. monocytogenes.We conclude that Nisin V possesses significant potential as a novel preservative or chemotherapeutic compound.
Affiliation: Department of Microbiology, University College Cork, Cork, Ireland.Show MeSH
Related in: MedlinePlus
Mentions: Having established the potency of Nisin V against L. monocytogenes using a variety of laboratory‚Äźbased assays, we sought to determine whether this enhanced effectiveness could be translated to a food matrix. This was particularly important given that the effectiveness of Nisin A in food can be influenced by a wide range of factors including fat content (Jung et‚ÄÉal., 1992; Davies et‚ÄÉal., 1999), proteolytic degradation (Murray and Richard, 1997), partitioning into polar or nonpolar food components (Murray and Richard, 1997) and sodium chloride concentrations (Chollet et‚ÄÉal., 2008). Thus, to evaluate the efficacy of Nisin V in a situation where Nisin A is traditionally used, the efficacy of Nisin A, Nisin V and Nisin T was compared using frankfurters, a food frequently associated with L. monocytogenes contamination, spiked with a strain L. monocytogenes F2365 associated with an epidemic outbreak of listeriosis (Linnan et‚ÄÉal., 1988; Mascola et‚ÄÉal., 1988). Previously, L. monocytogenes F2365 was tagged with a luciferase‚Äźbased reporter system that allows for real‚Äźtime monitoring in food as well as in vivo locations (Riedel et‚ÄÉal., 2007). The resultant strain was named F2365lux. For food assays, a commercially available frankfurter was homogenized and placed into sterile containers to which L. monocytogenes F2365lux was added to a concentration of 1‚ÄÉ√ó‚ÄÉ107‚ÄÉcfu‚ÄÉl‚ąí1. Each homogenate of 0.2‚ÄÉml was transferred to multiwell plates and bioluminescence was quantified using a Xenogen IVIS 100 imager (Time T0). Purified Nisin A, Nisin V or Nisin T peptide was then added to reach a final concentration of 7.5‚ÄÉmg‚ÄÉl‚ąí1. Following incubation at 37¬įC for 1‚ÄÉh, bacterial growth was monitored by both bioluminescence imaging (RLU) and plate counts. In the presence of either Nisin A or Nisin T L. monocytogenes F2365lux numbers increased as indicated by increased bioluminescence from 2.54+E05 relative light units (RLU) and 2.64+E05 RLU to 3.16+E05 RLU and 3.64+E05 RLU, respectively) after 1‚ÄÉh (Fig.‚ÄÉ3) whereas in the corresponding Nisin V‚Äźtreated samples, there was a marked decrease in bioluminescence from 2.53+E05 RLU to 1.71+E05 (Fig.‚ÄÉ3). CFU counts after 1‚ÄÉh established that this difference in bioluminescence corresponded to the presence of almost 1 log fewer F2365lux cells in the Nisin V‚Äźtreated frankfurter (9.45‚ÄÉ¬Ī‚ÄÉ2.7%) relative to the numbers present in the Nisin A‚Äź and Nisin T‚Äźtreated samples [100% and 89.16‚ÄÉ¬Ī‚ÄÉ20.8% respectively (Fig.‚ÄÉ3)]. While these results are in close agreement with the broth‚Äźbased kill curve experiments described above, they are important in their own right in that they demonstrate that the enhanced potency of Nisin V is maintained even within a complex and high‚Äźfat food matrix (total fat content 31.5%). This is reassuring given the problems associated with the inactivity of Nisin in certain foods.
Affiliation: Department of Microbiology, University College Cork, Cork, Ireland.