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...

Extraction of RNA from eukaryotic cells is a crucial stage in many molecular biology studies. Thus it is essential to use the most appropriate method that maximizes the yield and maintains the integrity of extracted RNA. The present work compared five manual RNA extraction methods of different dilutions of rabbit blood. The assessment of the concentration and purity of the extracted RNA were used as parameters to evaluate the efficiency of each method. Statistical analysis showed that the most effective method for RNA extraction from rabbit blood is by following the protocol of the RNeasy Lipid Tissue kit, but it requires the use of toxic reagents. The most efficient kit using no toxic reagents is the RNeasy protect animal blood.