Genome Sequence of Listeria monocytogenes Strain F4244, a 4b Serotype.

Listeria monocytogenes is an opportunistic invasive foodborne pathogen. Here, we performed whole-genome sequencing of L. monocytogenes strain F4244 (serotype 4b) using Illumina sequencing. The sequence showed 94.5% identity with strain F2365, serotype 4b, and 90.6% with EGD-e, serotype 1/2a.

GENOME ANNOUNCEMENT

Listeria monocytogenes is a Gram-positive facultative anaerobic bacterial pathogen. Although presently ubiquitous in the environment, L. monocytogenes is often associated with foods such as raw produce, ready-to-eat deli meats, and unpasteurized dairy products. Listeriosis, or systemic infection with L. monocytogenes, is a potentially fatal condition, particularly in the immunocompromised population with a disproportionate risk of perinatal death and maternal infection in late-stage pregnancy. Given the high morbidity, albeit low incidence, L. monocytogenes is considered one of the most important microbial concerns within the food industry (1). The canonical infectious mechanism of L. monocytogenes is well described (2). However, work from our group has identified an alternative paracellular pathogenic pathway during the intestinal phase of infection and a discrepancy of this pathogenic phenotype across different L. monocytogenes strains influenced by the gene product of locus lmo1634, an AdhE homolog called the Listeria adhesion protein (3–7). The genome of L. monocytogenes strain F4244, serotype 4b, isolated from cerebrospinal fluid of a patient and obtained from the Centers for Disease Control and Prevention (CDC, Atlanta, GA) was sequenced to help elucidate a context for the differences observed for paracellular translocation.

The whole genome was sequenced from paired-end libraries (TruSeq DNA sample preparation kit, Illumina, San Diego, CA, USA) using 10% of an Illumina HiSeq 2500 lane. Reads were assembled using ABySS-PE v1.2.7 utilizing the reads with kmer set to 90 bases. Remaining gaps were closed using conventional PCR followed by Sanger sequencing giving a contiguous sequence of 2,994,740 bases. The resulting genome was annotated using the NCBI Prokaryotic Genome Annotation Pipeline (https://www.ncbi.nlm.nih.gov/genome/annotation_prok/). Annotation revealed 3,062 genes in total, of which 2,954 are protein coding, 85 are RNAs (14 rRNAs, 67 tRNAs, and 4 noncoding RNAs [ncRNAs]), and 23 are pseudogenes. Alignment of the determined genome with published genomes for L. monocytogenes Clip80459 (GenBank accession number NC_012488) and F2365 (NC_002973) show 94.8% and 94.5% identity, suggesting general conservation with the serotype 4b group of lineage I (8). This contrasts to L. monocytogenes strains EGD-e (NC_003210), EGD (NC_022568), and 10403S (NC_017544), with 90.6%, 89.9%, and 90.0% identities, respectively, all of serotype 1/2a group of lineage II (9). Analysis of the lmo1634 locus (AdhE or LAP) from F4244 with these genomes demonstrates 99% sequence identity with Clip80459 and F2365 and 97% with EGD-e and EGD. This corresponds to a two-amino-acid substitution in Clip80459 and F2365 (G495V and S496Q), two additional substitutions in EGD and 10403S (K279N and A515S), and a fifth substitution in EGD-e (V202L).

Accession number(s).

These whole-genome and plasmid sequences have been deposited at GenBank under the accession numbers CP015508 and CP015509, respectively.