ABSTRACT
The lantibiotic nisin is used as a food additive to effectively inactivate a broad spectrum of Gram-positive bacteria such as Listeria monocytogenes. In total, 282 L. monocytogenes field isolates from German ready-to-eat food products, food-processing environments and patient samples and 39 Listeria reference strains were evaluated for their susceptibility to nisin. The MIC90 value was <1500â¯IUâ¯ml-1. Whole genome sequences (WGS) of four nisin susceptible (NS; growth <200â¯IUâ¯ml-1) and two nisin resistant L. monocytogenes field isolates (NR; growth >1500â¯IUâ¯ml-1) of serotype IIa were analyzed for DNA sequence variants (DSVs) in genes putatively associated with NR and its regulation. WGS of NR differed from NS in the gadD2 gene encoding for the glutamate decarboxylase system (GAD). Moreover, homology modeling predicted a protein structure of GadD2 in NR that promoted a less pH dependent GAD activity and may therefore be beneficial for nisin resistance. Likewise NR had a significant faster growth rate compared to NS in presence of nisin at pHâ¯7. In conclusion, results contributed to ongoing debate that a genetic shift in GAD supports NR state.
Subject(s)
Anti-Bacterial Agents/pharmacology , Bacterial Proteins/chemistry , Glutamate Decarboxylase/chemistry , Listeria monocytogenes/drug effects , Nisin/pharmacology , Bacterial Proteins/genetics , Bacterial Proteins/metabolism , Drug Resistance, Bacterial , Fast Foods/microbiology , Food Additives/pharmacology , Food Handling/methods , Glutamate Decarboxylase/genetics , Glutamate Decarboxylase/metabolism , Humans , Listeria monocytogenes/genetics , Listeria monocytogenes/isolation & purification , Listeria monocytogenes/metabolism , Protein Conformation/drug effects , Whole Genome SequencingABSTRACT
Nisin is frequently added as food additive to soft cheese to increase food safety against foodborne pathogens like Listeria monocytogenes. The goal of this study was the extension of the antimicrobial activity of nisin in sour curd cheese (SCC) by self-releasing adsorbed nisin from Neusilin UFL2 over production-based pH shift. First, the antimicrobial activity of nisin adsorbed to Neusilin UFL2 (UFL2-N) and free nisin was investigated in BHI broth at a pH range from 7.5 to 4.5 for each of six L. monocytogenes field isolates. UFL2-N showed similar minimal inhibition concentration to L. monocytogenes over time as free nisin. Distribution of nebulized, fluorescence-labelled UFL2 was homogenous on SCC surface. Thereafter, SCC surface was inoculated with L. monocytogenes and 0.004, 0.013, 0.026, and 0.132 mg mL-1 UFL2-N or free nisin. In SCC, L. monocytogenes was below quantification limit at 0.132 mg mL-1 UFL2-N or free nisin after 2 days of ripening. Collectively, UFL2-N enabled a slow release and antilisterial activity in vitro as well as in cheese manufacturing.
