Aim: To investigate the susceptibility of Pediococcus species to antimicrobial agents.
Methods and Results: The susceptibility to 14 antimicrobial agents of 31 genotypically distinct strains of six Pediococcus species was assessed by using Etests on ISO‐sensitest agar supplemented with horse blood. The species included were Pediococcus acidilactici, Pediococcus damnosus, Pediococcus dextrinicus, Pediococcus inopinatus, Pediococcus parvulus and Pediococcus pentosaceus. For several antimicrobial agents, some species were more susceptible than others. The two industrially important species, P. acidilactici and P. pentosaceus, differed with respect to erythromycin and trovafloxacin susceptibility, and in general both species had higher minimum inhibitory concentrations than the other species. In an erythromycin‐resistant P. acidilactici, an erythromycin resistance methylase B [erm(B)] gene was identified by PCR. Using a plasmid preparation from strain P. acidilactici 6990, a previously erythromycin‐sensitive Lactococcus lactis strain was made resistant. Transformants harboured a single plasmid, sized at 11·6 kb through sequence analysis. In addition, the erm(B) gene was identified within the plasmid sequence.
Conclusions: The phenotypic test indicated the absence of acquired antimicrobial resistance genes in 30 of the strains.
Significance and Impact of the Study: These results will help in selection of the best Pediococcus strains for use as starter cultures.
Aims: A live Lactococcus lactis culture, producing the two‐component broad spectrum bacteriocin lacticin 3147, was assessed for ability to inhibit the food pathogen Listeria monocytogenes on the surface of smear‐ripened cheese.
Methods and Results: In initial experiments, the addition of Listeria to a lacticin 3147‐containing fermentate produced with L. lactis DPC4275 (a transconjugant strain derived from L. lactis DPC3147) resulted in at least a 4 log reduction of the pathogen in 30 min. Two separate trials were performed in order to assess the most suitable method for application of the potential protective culture to smear‐ripened cheese. In the initial trial, the L. lactis was sprayed onto the surface of the cheese either before or after Listeria was deliberately applied. Application of the culture following Listeria challenge, yielded up to a 1000‐fold reduction of the pathogen in contrast to the pretreatment where Listeria numbers were unaffected. In a further trial, three applications of the live lacticin 3147‐producing culture was used on a cheese surface containing Listeria. Listeria numbers were found to be up to 100‐fold lower than in the cheese treated with L. lactis DPC4268 (control).
Conclusion: While application of the live lacticin 3147 producer did not give complete elimination of the pathogen the results nonetheless demonstrate the potential of the bioprotectant for improving the safety of smear‐ripened cheeses and particularly those that contain low level contamination with Listeria.
Significance and Impact of the Study: The application of lacticin 3147 as a live‐culture can serve as a bioprotectant for the control of L. monocytogenes on the surface of smear‐ripened cheese.
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