SUMMARY Salmonella is one of the most common causes of foodborne infection in Europe with Salmonella enterica serovar Enteritidis ( S . Enteritidis) being the most commonly identified serovar. The predominant phage type for S . Enteritidis is phage type (PT) 4, although PT 8 has increased in incidence. Within these phage types, pulsed-field gel electrophoresis (PFGE) provides a method of further subdivision. The international project, Salm-gene, was established in 2001 to develop a database of PFGE profiles within nine European countries and to establish criteria for real-time pattern recognition. It uses DNA fingerprints of salmonellas to investigate outbreaks and to evaluate trends and emerging issues of foodborne infection within Europe. The Salm-gene database contains details of about 11 700 S . Enteritidis isolates, demonstrating more than 65 unique PFGE profiles. The clonal nature of S . Enteritidis is evidenced by the high similarity and distribution of PFGE profiles. Over 56% (6603/11 716) of the submitted isolates of several different phage types were profile SENTXB.0001, although this profile is most closely associated with PT 4. The next most common profiles, SENTXB.0002 and SENTXB.0005, were closely associated with PT 8 and PT 21 respectively. Studies to investigate the relationship of profile types with outbreaks and possible vehicles of infection suggest that the incidence of PFGE profile SENTXB.0002, and thus PT 8, in some countries may be due to importation of foods or food production animals from Eastern Europe, where PT 8 is amongst the most frequently identified phage types. Collation of subtyping data, especially in the commonly recognized phage types, is necessary in order to evaluate trends and emerging issues in salmonella infection.
We present the first documented human case of Salmonella enterica serovar Apapa infection, isolated concurrently from a hospital inpatient and a pet lizard. The isolates were identical by biochemical profiling and pulsed-field gel electrophoresis. This rare serotype is known to be associated with reptiles. The current practice for avoiding reptile-associated infections is reviewed.
Variable-number tandem repeats (VNTRs) may evolve so rapidly that multiple profiles emerge during an outbreak. A total of 190 isolates from eight Salmonella enterica serovar Typhimurium outbreaks and 15 isolates from seven patients were analyzed by pulsed-field gel electrophoresis and VNTR typing. Small changes in loci were noted; otherwise, the VNTR profiles were stable during the course of the outbreaks.
An external quality assessment of PFGE method to discriminate between salmonella serotypes and lysotypes was carried out by the Salm-Gene project in Europe. A set of 16 strains of S. Enteritidis was sent to 9 national salmonella reference laboratories. By using a harmonised protocol, the PFGE profiles produced were comparable between each centre. In most cases, there was at least 90% similarity between isolates tested in the different European laboratories and there was usually >95% similarity. This suggests that PFGE analyses are reproducible and therefore can be used as a valuable investigation tool combined with epidemiological data.
This study investigates the distribution of pulsed-field gel electrophoresis (PFGE) profiles within Salmonella enterica serotype Enteritidis phage type (PT) 4 and S . Typhimurium definitive phage type (DT) 104, from cases of human infection in nine European countries from 2000 to 2004. Isolates were subtyped using standardized methods and gel images submitted by each participating country to the coordinating centre (Health Protection Agency Centre for Infections, London, UK), where they were entered into a central database, developed within BioNumerics software, and designated using an agreed nomenclature. S . Enteritidis PT4 ( n =3637) was differentiated into 38 different profiles. Simpson's index of diversity ( D ) of profiles ranged from 0·2 to 0·4. Profile SENTXB.0001 represented at least 80% of all profiles in each country. S . Typhimurium DT104 ( n =1202) was differentiated into 28 different profile types. Simpson's D was at least 0·6 in all countries except in Austria and Italy. In both these countries over 74% of S . Typhimurium DT104 profiles were STYMXB.0013. Profile STYMXB.0061, was predominant in Denmark, Spain, Finland and England & Wales where it represented between 36% and 45% of profiles. Profile STYMXB.0001 represented nearly half of all profiles in Scotland and 23% in England & Wales. PFGE is proving useful for further discrimination within S . Enteritidis PT4 and S . Typhimurium DT104. Ascertainment of international outbreaks involving common serotypes and phage types may be increased by the timely pooling of PFGE profiles within a central database readily accessible to all participating countries.
Abstract Rapid and accurate differentiation of Salmonella spp. causing enteric fever from non-typhoidal Salmonella is essential for clinical management of cases, laboratory risk management and implementation of public health measures. Current methods used for confirmation of identification including biochemistry and serotyping as well as whole genome sequencing analyses, takes several days. Here we report the development and evaluation of a real-time PCR assay that can be performed directly on crude DNA extracts from bacterial colonies, for the rapid identification of typhoidal and non-typhoidal Salmonella . This novel two-hour assay identifies the genus Salmonella by detecting the ttr gene, encoding tetrathionate reductase, and defines typhoidal Salmonella by the detection of S . Typhi and Paratyphi-specific gene combinations. PCR assay performance was determined using 211 clinical cultures of Salmonella (114 non-typhoidal and 97 Typhoidal strains) and 7 clinical non-Salmonella cultures. In addition, the specificity of the assay was evaluated in silico using a diverse in-house collection of 1882 Salmonella whole genome sequences. The real-time PCR results for 218 isolates and the genomic analysis of the 1882 isolates produced 100% sensitivity and 100% specificity (based on a 7 gene profile) for identifying typhoidal Salmonella compared to the Salmonella whole genome sequening identification methods currently used at Public Health England. This paper describes a robust real-time PCR assay for the rapid, accurate identification of typhoidal and non-typhoidal Salmonella which will be invaluable for the urgent screening of isolates from symptomatic individuals, the safe processing of isolates in laboratories and for assisting the management of public health risks.
In June 2001, as part of a microbiological study of bagged, ready-to-eat salad products, Salmonella enterica serotype Newport was isolated from a sample of pre-packed green salad distributed by a major supermarket retailer. The strain was characterised by phage typing, plasmid profile typing and pulsed-field gel electrophoresis. Other isolates of S. Newport from cases of human infection in England and Wales in the first six months of 2001 were similarly characterised. Of 60 strains from cases of human infection, 19 were found to be indistinguishable from that isolated from the salad product. This study highlights the benefits of an integrated approach to outbreak investigations, involving the various elements of the PHLS and the Food Standards Agency, and acknowledges the full co-operation of the retailer in ensuring the rapid withdrawal of the contaminated product.
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