ena-PROJECT-DTU Food-19-09-2012-15:24:57:541-5
The predicted proteomes of two food processing persistent Listeria monocytogenes strains isolated 6 years apart are highly homologous as revealed by full genome analyses
Listeria monocytogenes is a food-borne human pathogenic bacterium that can cause infections with a high mortality rate. It has a remarkable ability to persist in food processing facilities.  Here we report the complete genome sequences for two L. monocytogenes strains (N53-1 and La111) that were isolated six years apart from two different Danish fish processers. Both strains are serotype 1/2a and belong to a highly persistent DNA subtype (RAPD 9) isolated several times in Denmark. We here demonstrate, using in silico analyses, that both strains belong to the MLST type ST121 that has been isolated as persistent sub-type in several European countries. The purpose of this study was to compare complete genomes and predicted proteomes to identify genes or proteins that could contribute to persistence. In a genome comparison, the two persistent strains were extremely similar and collectively differed from the reference lineage II strain, EGD-e. Also, they differed markedly from a lineage I strain (F2365).  On the proteome level, the two strains were almost identical, with a predicted protein homology at 99.94% differing at only 2 proteins. No Single Nucleotide Polymorphisms (SNPs) differences were seen between the two strains; by contrast, N53-1 and La111 differed from the EGD-e reference by 3,942 and 3,471 SNPs, respectively. We included a US persistent L. monocytogenes (F6854) in our comparisons. As compared to non-persistent strains, all three persistent strains were distinguished by two genome deletions; one, of 2,472 bp, typically contains the gene for inlF; the other, a gap of 3,017 bp, includes three genes potentially related to bacteriocin production and transport (lmo2774, lmo2775 and the 3’ terminal part of lmo2776). Further studies of highly persistent strains are required to determine if absence of these genes promotes persistence. Whilst the genome comparison did not point to a clear physiological explanation of the persistent phenotype, the remarkable similarity between the two strains indicate that sub-types with specific traits are selected for in the food processing environment, and that particular genetic and physiological factors are responsible for the persistent phenotype.
Listeria monocytogenes is a food-borne human pathogenic bacterium that can cause infections with a high mortality rate. It has a remarkable ability to persist in food processing facilities.  Here we report the complete genome sequences for two L. monocytogenes strains (N53-1 and La111) that were isolated six years apart from two different Danish fish processers. Both strains are serotype 1/2a and belong to a highly persistent DNA subtype (RAPD 9) isolated several times in Denmark. We here demonstrate, using in silico analyses, that both strains belong to the MLST type ST121 that has been isolated as persistent sub-type in several European countries. The purpose of this study was to compare complete genomes and predicted proteomes to identify genes or proteins that could contribute to persistence. In a genome comparison, the two persistent strains were extremely similar and collectively differed from the reference lineage II strain, EGD-e. Also, they differed markedly from a lineage I strain (F2365).  On the proteome level, the two strains were almost identical, with a predicted protein homology at 99.94% differing at only 2 proteins. No Single Nucleotide Polymorphisms (SNPs) differences were seen between the two strains; by contrast, N53-1 and La111 differed from the EGD-e reference by 3,942 and 3,471 SNPs, respectively. We included a US persistent L. monocytogenes (F6854) in our comparisons. As compared to non-persistent strains, all three persistent strains were distinguished by two genome deletions; one, of 2,472 bp, typically contains the gene for inlF; the other, a gap of 3,017 bp, includes three genes potentially related to bacteriocin production and transport (lmo2774, lmo2775 and the 3’ terminal part of lmo2776). Further studies of highly persistent strains are required to determine if absence of these genes promotes persistence. Whilst the genome comparison did not point to a clear physiological explanation of the persistent phenotype, the remarkable similarity between the two strains indicate that sub-types with specific traits are selected for in the food processing environment, and that particular genetic and physiological factors are responsible for the persistent phenotype.