Quantitative risk assessment of human salmonellosis from the consumption of a turkey product in collective catering establishments.

The quantitative risk assessment (QRA) approach recommended by the Codex Alimentarius Commission was used to assess the risk of human salmonellosis from the consumption of 'cordon bleu', a specific turkey product, in collective catering establishments (CCEs) of a French department. The complete process was modeled and simulated, from the initial storage in the CCE freezer to the consumption, using a Monte Carlo simulation software. Data concerning the prevalence of contaminated 'cordon bleu', the level of contamination of Salmonella, the cooking and storage process were collected from 21 CCEs and 8 retailers of 'cordon bleu' in the selected department. Thermal inactivation kinetics for Salmonella were established to estimate the effect of heat treatment on the concentration in the product and to calculate the dose that could be ingested by the consumer. The Beta-Poisson dose-response model of Rose and Gerba [Water Science and Technology 24 (1991) 29] with the specific parameters for Salmonella was used to estimate the probability of infection related to the ingestion of a particular dose and a factor was applied to estimate the probability of illness from ingestion. The individual risk of salmonellosis, the risk of outbreak and the number of cases were calculated using Monte Carlo simulation method. The risk of salmonellosis was close to zero when the 'cordons bleus' were cooked in the oven. Therefore, the risk was calculated for the fryer cooking since the insufficient cooking time observed was, sometimes, at the origin of low temperatures (37-89 degrees C). The influence of both the initial concentration of Salmonella in the product and the heat storage before consumption on the final risk was studied. For a high initial concentration of Salmonella in the product, when the 'cordons bleus' are fryer cooked, the average risk of salmonellosis was equal to 3.95 x 10(-3) without storage before consumption and 2.8 x 10(-4) if the product is consumed after storage. This paper presents the results of the QRA and discusses risk management options to minimize the risk of salmonellosis.

Evaluation of IS200-PCR and comparison with other molecular markers To trace Salmonella enterica subsp. enterica serotype typhimurium bovine isolates from farm to meat.

A procedure that uses an original molecular marker (IS200-PCR) and that is based on the amplification of DNA with outward-facing primers complementary to each end of IS200 has been evaluated with a collection of 85 Salmonella enterica subsp. enterica serotype Typhimurium isolates. These strains were isolated from a group of 10 cows at different stages: during transportation between the farm and the slaughterhouse, on the slaughter line, from the environment, and from the final product (ground beef). The 85 isolates were characterized by their antibiotic resistance patterns and were compared by IS200-PCR and by use of four other genotypic markers. Those markers included restriction profiles for 16S and 23S rRNA (ribotypes) and amplification profiles obtained by different approaches: random amplified polymorphic DNA analysis, enterobacterial repetitive intergenic consensus PCR, and PCR ribotyping. The results of the IS200-PCR were in accordance with those of other molecular typing methods for this collection of isolates. Five different genotypes were found, which made it possible to refine the hypotheses on transmission obtained from phenotypic results. The genotyping results indicated the massive contamination of the whole group of animals and of the environment by one clonal strain originally recovered from one cow that excreted the strain. On the other hand, a few animals and their environment appeared to be simultaneously contaminated with genetically different strains.

Salmonella typhimurium contamination from farm to meat in adult cattle. Descriptive study.

The aim of this work was to study the increase in hair contamination by salmonella in cattle between the farm and slaughterhouse and to explore the possible relationship between this contamination and the contamination of carcasses and of the ground beef made from these animals. Between April 1994 and May 1995, eight groups of ten cows were sampled at different stages during transportation between the farm and the slaughterhouse and on the slaughterline. For each group, one or two cows were included in each group because they had been shown to excrete Salmonella typhimurium 15 days before slaughtering. Samples were collected from the animals (faeces, hide, carcasses, lymph nodes, ears), from the environment (vehicles, cubicles, loading corridor, stunning area) and from the final product (ground beef). The hair samples as well as the environmental samples were the most frequently contaminated (26 to 69%). Eleven different salmonella serotypes were identified, with a maximum of three different serotypes per sample. The typhimurium serotype was isolated from 67% of the positive samples. For the animals leaving the farms, the frequency of hair contamination by serotype typhimurium was 8%. The step that most influenced hair contamination seemed to be the transportation to the slaughterhouse with the contamination frequency reaching 25%. The time spent by the animals in the cubicles of the waiting area of the slaughterhouse seemed to have little influence on the frequency of hair contamination. Even though the frequency of coat contamination reached 25% (for serotype typhimurium) at the beginning of the slaughterline, carcass contamination was only 1% before chilling and only involved one group of animals. In this group, hair contamination after slaughter (serotype typhimurium) reached 90% (9/10), and 80% (4/5) of the samples taken from the ground beef were positive (serotype typhimurium). No contamination was detected in the ground meat made from the other groups.

Characterization and distribution of two insertion sequences, IS1191 and iso-IS981, in Streptococcus thermophilus: does intergeneric transfer of insertion sequences occur in lactic acid bacteria co-cultures?

A chromosomal repeated sequence from Streptococcus thermophilus was identified as a new insertion sequence (IS), IS1191. This is the first IS element characterized in this species. This 1313 bp element has 28 bp imperfect terminal inverted repeats and is flanked by short direct repeats of 8 bp. The single large open reading frame of IS1191 encodes a 391-amino-acid protein which displays homologies with transposases encodes by IS1201 from Lactobacillus helveticus (44.5% amino-acid sequence identity) and by the other ISs of the IS256 family. One of the copies of IS1191 is inserted into a truncated iso-IS981 element. The nucleotide sequences of two truncated iso-IS981s from S. thermophilus and the sequence of IS981 element from Lactococcus lactis share more than 99% identity. The distribution of these insertion sequences in L. lactis and S. thermophilus strains suggests that intergeneric transfers occur during cocultures used in the manufacture of cheese.

Strain characterization, genome size and plasmid content in the Lactobacillus acidophilus group (Hansen and Mocquot).

Chromosomal DNA of nine strains of the Lactobacillus acidophilus (Hansen and Mocquot) group in which heterogeneity had previously been revealed by biochemical characteristics and DNA-DNA hybridization studies were further investigated by restriction analysis, Southern hybridization, conventional and pulsed-field gel electrophoresis (PFGE) analyses. Industrial strains were characterized and identified as Lact. acidophilus. For this species, the number of rRNA gene clusters was estimated to be at least four from analyses of rRNA gene restriction patterns. The chromosome size of type-strains of Lact. acidophilus and Lact. gasseri was estimated from PFGE analysis to be 1.85 and 2.02 Mb respectively and Lact. gasseri strains were found to contain large-sized linear plasmids.

The 23S-5S spacer of two rRNA loci of Streptococcus salivarius subsp thermophilus includes a promoter.

The nucleotide sequence of the 3' part of a ribosomal and transfer RNA locus from Streptococcus salivarius subsp thermophilus NST1403 was determined. The sequenced DNA fragment includes the 3' end of a 23S rRNA gene, a 5S rRNA gene, a tRNA(asn) gene and a potential transcriptional terminator. The tRNA gene does not encode for the CCA 3'terminus of mature tRNA. We compared this sequence to a promoter-carrying DNA fragment sequence (P20) of Streptococcus salivarius subsp thermophilus A054 [1]. We found that the P20 sequence included the 3' end of a 23S rRNA gene, a 5S rRNA gene and the 5' part of a tRNA(val) gene. The two 23S-5S spacer sequences are identical and contain a promoter and a potential 23S rRNA processing site. Therefore, 5S rRNA and tRNA genes could be transcribed from a promoter located within the 23S-5S spacer of at least two of the six rRNA loci.

Detection of intraspecific DNA polymorphism in Streptococcus salivarius subsp. thermophilus by a homologous rDNA probe.

Three ribosomal probes from Streptococcus salivarius subsp. thermophilus were cloned. Sequence data demonstrate that their juxtaposition corresponds to an entire operon. They were used in order to study ribosomal operon number and organization. rRNA genes were shown to be clustered in the order 5'-16S-23S-5S-3' and the number of rrn loci to vary within the subspecies. The smallest of the 3 probes was used for strain characterization. Substantial variability in hybridization patterns was observed among strains, resulting not only from, restriction fragment length polymorphism (RFLP) but also from the variability of ribosomal operon number.

A species-specific DNA probe obtained from Streptococcus salivarius subsp. thermophilus detects strain restriction polymorphism.

Genomic polymorphism in Streptococcus salivarius subsp. thermophilus was revealed by DNA restriction pattern analysis. A 4.2-kb variable DNA fragment was cloned from strain NST7 and hybridised with the DNA of 25 strains allowing an easy detection of intraspecific RFLP. Strong and weak hybridisation signals were observed and the latter were specifically revealed by a 2.1-kb fragment of the probe. Probe specificity was demonstrated by the absence of homology with DNA of strains belonging to 10 other species, with the exception of S. salivarius subsp. salivarius, confirming a close relationship between S. salivarius and S. thermophilus.