Properties of Listeria monocytogenes on Acquisition of Pediocin Resistance

A class IIa bacteriocin pediocin can be used in food biopreservation due to its high activity against foodborne pathogens, such as Listeria monocytogenes. In this study, pediocin-resistant L. monocytogenes variants were generated, and different properties of the mutants were compared with wild-type L. monocytogenes. Bacteriocin-resistant Listeria variants were selected on BHI agar containing pediocin. Susceptibility of Listeria strains to different bacteriocins and antibiotics were tested by agar well diffusion method. Growth properties were monitored by recording absorbance at 600nm. Changes in cell properties were evaluated by determining cell surface hydrophobicity and adsorption of pediocin onto Listeria cells. Transcriptional levels of mptA gene in wild-type and mutant strains were quantified by real-time PCR. Mutations in DNA were examined by sequencing. The two stable resistant variants were less sensitive also to class IIa bacteriocins, but not to nisin and ampicillin. In BHI broth supplemented with glucose or mannose, the wild-type strain grew faster than the resistant variants, whereas with cellobiose, the mutants grew better. The bacteriocin-resistant cells showed increased hydrophobicity, as well as lower adsorption of pediocin on cell surface than wild-type Listeria. Significant downregulation of mptA gene was observed in Lmo-r2 variant but not in Lmo-r5 variant. However, no mutations in the regulatory genes resD and lmo0095 of the variants were observed, and only minor changes were found in upstream region of the mpt operon. These results demonstrated differences in growth, carbohydrate utilization, cell surface, and gene transcription between wild-type and pediocin-resistant strains. This makes it evident that bacteria can use various and complex ways to acquire resistance to antimicrobial compounds.