Molecular genotype analysis of Salmonella bovismorbificans

Detection and differentiation of Salmonella Enteritidis and Salmonella Typhimurium by multiplex quantitative PCR from different poultry matrices

1. The aim of this study was to develop a multiplex quantitative polymerase chain reaction (qPCR) based molecular diagnostic kit for rapid diagnosis of Salmonella enterica serovar Enteritidis and S. enterica serovar Typhimurium serotypes, which are frequently isolated worldwide from poultry samples.2. Detection and discrimination of S. Enteritidis and S. Typhimurium were performed by targeting the sdf and the STM4492 (putative cytoplasmic protein) gene, respectively. The invA (invasion protein) gene was used to detect Salmonella spp. as a target gene, since it is considered a standard. In this study, a total of 200 bacterial strains (178 Salmonella spp. strains and 22 other genera) were used to test the specificity and sensitivity of the developed kit. The limit of detection (LOD) of the assays was determined to be 10⁰-10¹ cfu/25 g from chicken meat samples artificially contaminated by litter and 10⁰-10¹ cfu/ml for cloacal swab samples.3. The multiplex qPCR results were 100% compatible with conventional serotyping results while the specificity and sensitivity values were 100%. These findings indicated that the newly developed multiplex qPCR technique can provide an alternative method to conventional serotyping of S. Enteritidis and S. Typhimurium in laboratories lacking adequate infrastructure.

Genomic characterisation of invasive non-typhoidal Salmonella enterica Subspecies enterica Serovar Bovismorbificans isolates from Malawi

Background

Invasive Non-typhoidal Salmonella (iNTS) are an important cause of bacteraemia in children and HIV-infected adults in sub-Saharan Africa. Previous research has shown that iNTS strains exhibit a pattern of gene loss that resembles that of host adapted serovars such as Salmonella Typhi and Paratyphi A. Salmonella enterica serovar Bovismorbificans was a common serovar in Malawi between 1997 and 2004.

Methodology

We sequenced the genomes of 14 Malawian bacteraemia and four veterinary isolates from the UK, to identify genomic variations and signs of host adaptation in the Malawian strains.

Principal Findings

Whole genome phylogeny of invasive and veterinary S. Bovismorbificans isolates showed that the isolates are highly related, belonging to the most common international S. Bovismorbificans Sequence Type, ST142, in contrast to the findings for S. Typhimurium, where a distinct Sequence Type, ST313, is associated with invasive disease in sub-Saharan Africa. Although genome degradation through pseudogene formation was observed in ST142 isolates, there were no clear overlaps with the patterns of gene loss seen in iNTS ST313 isolates previously described from Malawi, and no clear distinction between S. Bovismorbificans isolates from Malawi and the UK.

The only defining differences between S. Bovismorbificans bacteraemia and veterinary isolates were prophage-related regions and the carriage of a S. Bovismorbificans virulence plasmid (pVIRBov).

Conclusions

iNTS S. Bovismorbificans isolates, unlike iNTS S. Typhiumrium isolates, are only distinguished from those circulating elsewhere by differences in the mobile genome. It is likely that these strains have entered a susceptible population and are able to take advantage of this niche. There are tentative signs of convergent evolution to a more human adapted iNTS variant. Considering its importance in causing disease in this region, S. Bovismorbificans may be at the beginning of this process, providing a reference against which to compare changes that may become fixed in future lineages in sub-Saharan Africa.

Bacteraemia and meningitis caused by non-typhoidal Salmonella (including serovars Typhimurium, Enteritidis and Bovismorbificans) are a serious health issue in sub-Saharan Africa, particularly in young children and HIV-infected adults. Previous work has indicated that a distinct S. Typhimurium sequence type, ST313, has evolved and spread in these countries, and may be more human-adapted than isolates found in the developed world. We therefore investigated the genomes of Salmonella enterica serovar Bovismorbificans bacteraemia isolates from Malawi and compared them to genomes of veterinary S. Bovismorbificans isolates from the UK using Next Generation Sequencing Technology and subsequent genomic comparisons to establish if there is a genetic basis for this increase in invasive disease observed among African NTS. Contrary to the previous findings for S. Typhimurium, where a distinct ST is found only in sub-Saharan Africa, we discovered that the S. Bovismorbificans isolates from Malawi belong to the most common ST of the serovar and the genome is highly conserved across all sequenced isolates. The major differences between UK veterinary and African human isolates were due to prophage regions inserted into the genomes of African isolates, coupled with a higher prevalence of a virulence plasmid compared to the UK isolates.

High-throughput molecular determination of salmonella enterica serovars by use of multiplex PCR and capillary electrophoresis analysis

Salmonella enterica is a leading cause of food-borne illness worldwide and is also a major cause of morbidity and mortality in domestic and wild animals. In the current study, a high-throughput molecular assay was developed to determine the most common clinical and nonhuman serovars of S. enterica in the United States. Sixteen genomic targets were identified based on their differential distribution among common serovars. Primers were designed to amplify regions of each of these targets in a single multiplex PCR while incorporating a 6-carboxyfluorescein-labeled universal primer to fluorescently label all amplicons. The fluorescently labeled PCR products were separated using capillary electrophoresis, and a Salmonella multiplex assay for rapid typing (SMART) code was generated for each isolate, based upon the presence or absence of PCR products generated from each target gene. Seven hundred fifty-one blind clinical isolates of Salmonella from Washington State, collected in 2007 and previously serotyped via antisera, were screened with the assay. A total of 89.6% of the isolates were correctly identified based on comparison to a panel of representative SMART codes previously determined for the top 50 most common serovars in the United States. Of the remaining isolates, 6.2% represented isolates that produced a new SMART code for a previously determined serotype, while the final 8.8% were from serotypes not screened in the original panel used to score isolates in the blinded study. This high-throughput multiplex PCR assay allowed simple and accurate typing of the most prevalent clinical serovars of Salmonella enterica at a level comparable to that of conventional serotyping, but at a fraction of both the cost and time required per test.

Multiplex PCR-based method for identification of common clinical serotypes of Salmonella enterica subsp. enterica

A multiplex PCR method has been developed to differentiate between the most common clinical serotypes of Salmonella enterica subsp. enterica encountered in Washington State and the United States in general. Six genetic loci from S. enterica serovar Typhimurium and four from S. enterica serovar Typhi were used to create an assay consisting of two five-plex PCRs. The assays gave reproducible results with 30 different serotypes that represent the most common clinical isolates of S. enterica subsp. enterica. Of these, 22 serotypes gave unique amplification patterns compared with each other and the other 8 serotypes were grouped into four pairs. These were further resolved by two additional PCRs. We compared the data from PCR serotyping with conventional serotyping and found that PCR serotyping was nearly as discriminatory as conventional serotyping was. The results from a blind test screening 111 clinical isolates revealed that 97% were correctly identified using the multiplex PCR assay. The assay can be easily performed on multiple samples with final results in less than 5 h and, in conjunction with pulsed-field gel electrophoresis, forms a very robust test method for the molecular subtyping of Salmonella enterica subsp. enterica.

Strain discrimination of a novel serotype of Salmonella from harbour porpoises (Phocoena phocoena) by molecular techniques

The relatedness of 41 isolates of Salmonella of a novel serotype (antigenic formula 4,12:a:-) of serogroup B, obtained from harbour porpoises (Phocoena phocoena) stranded at various sites around the coastline of Scotland, was assessed by two molecular typing methods. Ribotyping showed that these isolates belonged to seven EcoRI (E) ribotypes and 11 PstI (P) ribotypes that were, in each case, distinct but closely related. Combined ribotyping data identified 15 different E/P ribotypes, the most common of which, E1/P1, was represented by 15 isolates from 14 animals stranded on both east and west coastlines. Strain discrimination achieved by E/P ribotyping was high (D=0.84). IS200 profiling revealed only three different fingerprints and strain discrimination by this method alone was poor (D=0.39). When E/P ribotyping and IS200 profiling were used together, they revealed the existence of 17 different types among the 41 isolates which formed two distinct, but related, groups of Salmonella serotype 4,12:a:-. This information should prove helpful in future studies examining the mode of transmission of this novel salmonella serotype and its association with disease in harbour porpoises.

Assessment of strain relatedness among Salmonella serotypes Salinatis, Duisburg, and Sandiego by biotyping, ribotyping, IS200 fingerprinting, and pulsed-field gel electrophoresis

Salinatis (antigenic formula, 4,12:d:eh:enz15) is a rare Salmonella serotype currently designated a triphasic variant of the diphasic serotype Duisburg (1,4,12,27:d:enz15) (underlining indicates that the O antigen is determined by phage lysogenization). Salinatis could also be related to serotype Sandiego (4,[5],12:eh:enz15), from which it might have been derived by loss of H-d flagellin genes. Nineteen Salmonella strains of serotypes Salinatis, Duisburg, and Sandiego were examined by biotyping, PvuII and SmaI ribotyping, IS200 fingerprinting, and pulsed-field gel electrophoretic profiling. Results from these methods, used alone or together, indicate that serotype Salinatis is more likely to be related to serotype Sandiego than to serotype Duisburg. For future lists of serotype names, it is recommended that Salinatis be considered a variant of Sandiego.

Strain typing with IS200 fingerprints in Salmonella abortusovis

A collection of Salmonella abortusovis isolates was examined for the presence of insertion element IS200. All proved to contain three or four copies of the element. One IS200 hybridization band of approximately 9 kb was found in all isolates, indicating that all S. abortusovis strains carry an IS200 element in similar or identical locations; this band can be potentially useful for serovar identification. S. abortusovis collection isolates from distinct geographic areas were highly polymorphic, suggesting that IS200 fingerprints might provide information on the geographic origin of S. abortusovis strains. Isolates obtained from the same geographic area (the island of Sardinia, Italy) were less polymorphic: all shared three constant IS200 hybridization bands, indicating that they derive from a single ancestor. Most strains analyzed contained an additional copy of IS200 in the variable region of the virulence plasmid. Certain Sardinian flocks proved to be infected by only one S. abortusovis strain, while others harbored two strains. Strain typing with IS200 fingerprints proved to be more reliable than plasmid analysis, because the latter yielded a high degree of polymorphism, even among isolates from the same flock.

Differentiation of Salmonella serovar infantis isolates from human and animal sources by fingerprinting IS200 and 16S rrn loci

We genotyped Salmonella serovar infantis (referred to as S. infantis), which is the most widespread serovar among animals and the third most common cause of human salmonellosis in Finland. Molecular fingerprinting of the 16S rrn locus and the Salmonella-specific insertion sequence IS200 was used to type the 131 isolates originating from the main sources of S. infantis infection. The number of IS200 elements in S. infantis varied from zero to seven; three or more copies were present in 97% of the isolates, and 71% had four copies. There were four conserved chromosomal positions of IS200, which allowed us to group the isolates into three major clonal groups. We defined 11 unique IS200 profiles and five different ribotypes which, in combination, generated 15 genotypes highly restricted to the infection sources: 8 genotypes were typical of isolates from broiler chickens and cattle and seven genotypes were typical of isolates from humans. The eight genotypes of isolates from chickens represented two clonal groups which were differentially associated with chicken-producing companies. The typing scheme allows efficient discrimination between isolates from various infection sources and within sources and, therefore, provides a unique molecular tool for use in the study of the epidemiology of S. infantis infection.

Distinct genotypes of human and canine isolates of Campylobacter upsaliensis determined by 16S rRNA gene typing and plasmid profiling

The utility of combined 16S rRNA (rrs) gene restriction fragment length polymorphism and plasmid profiles to differentiate between and within Campylobacter upsaliensis of human and canine origin was examined. Fourteen distinct rrs gene restriction fragment length polymorphs consisting of bands sized between 1.9 and 4.8 kb were observed. The copy number of the 16S rRNA gene was three in most strains of C. upsaliensis. Plasmids were found in almost 60% of the strains; ranging in size from 1.5 to 100 kb, they gave 15 distinct plasmid profiles. All isolates from humans contained one or more plasmids, as did strains isolated from dogs with sporadic diarrhea. The two commonest 16S ribotypes were divided into eight and nine subgroups by plasmid profiling. The genotyping of canine isolates from three veterinary surveys detected both multiple infections and reinfection of dogs. Except for one, each of the isolates from humans constituted a single and unique 16S ribotype, and these more frequently carried plasmids than did canine strains. Ribotypes of human strains were not found among canine isolates. These results suggest that host-specific genotypic differences may exist among strains of C. upsaliensis, for example, intraspecific clones or clone complexes pathogenic for humans.

Insertion sequence IS200 fingerprinting of Salmonella typhi: an assessment of epidemiological applicability

When Pst I-generated digests of genomic DNA from each of the type strains of 49 of the Vi phage types of Salmonella typhi were probed with a PCR-amplified IS200 gene probe, all strains were found to possess at least 11 IS200 elements carried on fragments in the range 24.2-1.2 kb. Fourteen fingerprints were identified but two patterns designated IS200Sty1 and IS200Sty2 predominated. In one strain, a plasmid-mediated IS200 element was identified. When IS200 fingerprinting was applied to epidemiologically-unrelated strains of S. typhi isolated in Ecuador, 3 patterns were identified in 10 strains belonging to 9 different phage types. It is concluded that Vi phage typing remains the method of choice for the primary differentiation of S. typhi but that IS200 fingerprinting may be of limited use in laboratories which do not have access to phage typing.

Molecular subtyping within a single Salmonella typhimurium phage type, DT204c, with a PCR-generated probe for IS200

We report primers and conditions for the generation by PCR of a probe for the DNA insertion element IS200. This probe was shown to be suitable for genotypic subtyping within a single phage type of Salmonella typhimurium. A collection of isolates of DT204c, a phage type implicated in the spread of multiple drug resistance in bovine animals and to man, was analyzed. Three IS200 profiles, corresponding to related chromosomal genotypes were characterized in DT204c. Molecular discrimination within a single phage type of S. typhimurium has general significance for genotypic typing, and for the definition of epidemiological clonality in Salmonella.