Stress Survival Islet 1 (SSI-1) Survey in Listeria monocytogenes Reveals an Insert Common to Listeria innocua in Sequence Type 121 L. monocytogenes Strains

Abstract

Listeria monocytogenes strains (n ‫؍‬ 117) were screened for the presence of stress survival islet 1 (SSI-1). SSI-1؉ strains (32.5%) belonged mainly to serotypes 1/2c, 3b, and 3c. All sequence type 121 (ST-121) strains included (n ‫؍‬ 7) possessed homologues to Listeria innocua genes lin0464 and lin0465 instead of SSI-1.The genus Listeria comprises eight species:and the newly described L. rocourtiae and L. marthii (7,11,18). From a human perspective, the food-borne pathogen L. monocytogenes is the most important species of this genus. Recently, a stress survival islet (stress survival islet 1 [SSI-1]) has been identified in L. monocytogenes (29). Deletion mutants showed impaired growth at low pH and high salt concentrations. The islet was present in about 50% of tested L. monocytogenes strains, mainly those not belonging to serogroup 4. According to the sequence of L. monocytogenes EGD-e (serotype 1/2a), the islet contains five genes, lmo0444, lmo0445, lmo0446 (pva), lmo0447 (gadD1), and lmo0448 (gadT1), positioned between two genes highly conserved across different Listeria spp. An open reading frame (ORF) transcribed in the opposite direction is present at this location in L. monocytogenes strains without the islet (e.g., strain F2365, serotype 4b), and in L. innocua CLIP 11262, two genes transcribed in opposite directions (lin0464 and lin0465) are present at the same location (29). L. welshimeri SLCC 5334 does not contain any genes at this position. In L. seeligeri SLCC 3954, this region was similar to that in L. welshimeri SLCC 5334, with no open reading frame and with small differences in the lengths of the intergenic region, i.e., 281 bp (L. welshimeri FN557490) and 166 bp (L. seeligeri AM263198). There was 63% identity between a 46-bp stretch at the 5Ј end in L. welshimeri and that in L. seeligeri, both of which were followed by an L. welshimerispecific portion of 112 bp and a 123-bp stretch at the 3Ј end with 73.2% identity.In the present study, a collection of 117 L. monocytogenes strains, including isolates from cheese dairies, meat and meat products, fish, and veterinary and human infections, was screened by PCR for the presence of SSI-1 (Table 1; also see Table S1 in the supplemental material) (29). Serotypes were determined by classical serotyping and by a multiplex PCR method for grouping strains into four major serotype-related groups (9, 31). The predicted 9.7-kbp (SSI-1 ϩ ) and 1.1-kbp (SSI-1 Ϫ ) fragments were observed in 32.5% and 61.5% of strains, respectively ( Fig. 1; Table 2). SSI-1 was present in the majority of 1/2c, 3b, and 3c strains tested but in only one strain each of serotypes 4a and 4b. A single serotype 4c strain was included in the survey, and it contained SSI-1. The majority of serotype 4b, 1/2a, and 4a strains, as well as all strains with ambiguous serotype 4d or 4e, lacked SSI-1. Earlier findings suggest that SSI-1 is more prevalent in non-serogroup 4 strains, which was confirmed by our results: 50% of non-serogroup 4 strains but only 7.5% of serogroup 4 strains contained SS...

Genome Sequencing Identifies Two Nearly Unchanged Strains of Persistent Listeria monocytogenes Isolated at Two Different Fish Processing Plants Sampled 6 Years Apart

“…L. monocytogenes ST121 strains have also been reported in France, Italy, and Spain (34,46,47). By PCR, Hein et al (45) showed that the ST121 strain had a 2.2-kbp fragment (in N53-1 and La111), whereas the majority of serotype 1/2a strains had a 9.7-kbp fragment. The 9.7-kbp fragment is described as a five-gene stress survival islet (SSI-1) and contributes to growth under suboptimal conditions (41).…”

“…F6854 belongs to ST11, which corresponds to abcZ-7, bglA-6, cat-10, dapE-6, dat-1, ldh-2, and lhkA-1, and EGD-e belongs to ST35 (abcZ-6, bglA -5, cat-6, dapE-20, dat-1, ldh-4, and lhkA-1) (44). A recent study by Hein et al (45) described ST121 strains isolated in Austria and Belgium from different ecological niches, including food, food processing facilities, and human cases, over several years. Two of the strains were isolated from the same dairy plant over a course of at least 3 years.…”

“…A BLAST search of the 2.2-kbp fragment showed 95% identity with the two genes lin0464 and lin0465 from Listeria innocua CLIP 11262 (GenBank accession number AL596165.1). Hein et al (45) speculated that the two L. innocua genes lin0464 and lin0465 both contribute to fitness of the ST121 strains in the environment. Furthermore, the ST121 strains also had the same premature stop codon in inlA, leading to a truncated InlA, as in our two processing-persistent strains.…”

The Connection between Persistent, Disinfectant-Resistant Listeria monocytogenes Strains from Two Geographically Separate Iberian Pork Processing Plants: Evidence from Comparative Genome Analysis

“…In contrast, the particularly long persistence of ST31 (10,15) (Table 1) could be related to the presence of a region identical to the so-called stress survival islet 1 (SSI-1) (65). The five-gene SSI-1 can contribute to elevated resistance to several types of stress in certain strains of L. monocytogenes (65).…”

“…The MLST database of the Pasteur Institute in Paris, France (updated on 3 March 2015), includes only 10 ST31 strains and 69 ST121 strains (most are of the 1/2a serotype). The ST121 type has been isolated as a persistent type in food and food-associated environments in different countries (16,42,65,66). ST121 is among the six L. monocytogenes STs most prevalent worldwide (67) and seems to be well adapted to the colonization of meat-associated environments (67,68).…”