Salmonella Biofilms
Salmonella Biofilms: From food to human disease
from Robert W. Crawford, Geoffrey Gonzalez-Escobedo and John S. Gunn writing in Salmonella: From Genome to Function
Bacterial biofilms are increasingly implicated as burdens to food and public safety. Over the past few decades, we have learned that this sessile environment provides diverse species of bacteria selective advantages in natural, medical, and industrial ecosystems, as well as resistance to commonly administered antibiotics and protection from host immune responses during chronic infection of humans and animals. Salmonella spp. are food-borne pathogens that remain a critical health concern in impoverished and industrialized nations. In the laboratory, salmonellae have been shown to form biofilms on a variety of surfaces. These Salmonella spp. biofilms have been found to contaminate plant and animal food sources to cause human disease upon consumption, and/or to enhance salmonellae colonization of and persistence at sites of infection.
Further reading: Salmonella: From Genome to Function
from Robert W. Crawford, Geoffrey Gonzalez-Escobedo and John S. Gunn writing in Salmonella: From Genome to Function
Bacterial biofilms are increasingly implicated as burdens to food and public safety. Over the past few decades, we have learned that this sessile environment provides diverse species of bacteria selective advantages in natural, medical, and industrial ecosystems, as well as resistance to commonly administered antibiotics and protection from host immune responses during chronic infection of humans and animals. Salmonella spp. are food-borne pathogens that remain a critical health concern in impoverished and industrialized nations. In the laboratory, salmonellae have been shown to form biofilms on a variety of surfaces. These Salmonella spp. biofilms have been found to contaminate plant and animal food sources to cause human disease upon consumption, and/or to enhance salmonellae colonization of and persistence at sites of infection.
Further reading: Salmonella: From Genome to Function
Anti-Salmonella immunity
Anti-Salmonella immunity: Highlighting new research in vaccines, mucosal immunology and systemic disease
from Jennifer L. Bishop, Ellen T. Arena, Kenneth W. Harder and B. Brett Finlay writing in Salmonella: From Genome to Function
Enteric fever and non-typhoidal salmonelloses (NTS) are caused by a wide variety of Salmonella enterica serovars and are a serious health threat throughout the world. Immunity to systemic typhoid and NTS requires intricate crosstalk between both innate and adaptive immune cells spanning multiple organ systems. The development of a number of new mouse and in vitro culture models suitable for studying gastroenteritis has highlighted the complexity of mucosal responses and shown how a diverse subset of cells interact within the intestinal architecture to elicit anti-Salmonella immunity. These include specific dendritic cell subsets, natural killer cells and TH17 skewed T helper cells and the repertoire of cytokines they produce, including IL-17, IL-23, IL-22 and IL-15. Furthermore, the importance of commensal microflora has been stressed in various Salmonella models, and new research has shown the various effects of prebiotics, probiotics and antibiotics on Salmonella pathogenesis. Systemic immune responses are also more explicitly understood, as the location and phenotype of cells harboring intracellular bacteria become more defined. A forthcoming book reviews these recent advances and how they are being translated into new therapies and vaccine studies in the human population.
Read more: Salmonella: From Genome to Function
from Jennifer L. Bishop, Ellen T. Arena, Kenneth W. Harder and B. Brett Finlay writing in Salmonella: From Genome to Function
Enteric fever and non-typhoidal salmonelloses (NTS) are caused by a wide variety of Salmonella enterica serovars and are a serious health threat throughout the world. Immunity to systemic typhoid and NTS requires intricate crosstalk between both innate and adaptive immune cells spanning multiple organ systems. The development of a number of new mouse and in vitro culture models suitable for studying gastroenteritis has highlighted the complexity of mucosal responses and shown how a diverse subset of cells interact within the intestinal architecture to elicit anti-Salmonella immunity. These include specific dendritic cell subsets, natural killer cells and TH17 skewed T helper cells and the repertoire of cytokines they produce, including IL-17, IL-23, IL-22 and IL-15. Furthermore, the importance of commensal microflora has been stressed in various Salmonella models, and new research has shown the various effects of prebiotics, probiotics and antibiotics on Salmonella pathogenesis. Systemic immune responses are also more explicitly understood, as the location and phenotype of cells harboring intracellular bacteria become more defined. A forthcoming book reviews these recent advances and how they are being translated into new therapies and vaccine studies in the human population.
Read more: Salmonella: From Genome to Function
The Intracellular lifestyle of Salmonella
The intracellular lifestyle of Salmonella enterica and novel approaches to understand the adaptation to life within the Salmonella-containing vacuole
from Roopa Rajashekar and Michael Hensel writing in Salmonella: From Genome to Function
Salmonella enterica is a facultative intracellular pathogen that resides in a unique membrane-bound compartment, referred to as Salmonella-containing vacuole or SCV. Within the SCV, Salmonella is able to survive the antimicrobial activities of phagocytic cells and can rapidly multiply in a variety of host cells. Intracellular life of Salmonella is dependent on a large number of virulence traits, but the function of the type III secretion system (T3SS) encoded by Salmonella Pathogenicity Island 2 (SPI2) is of central importance. Although more than 20 effector proteins have been identified as translocated by the SPI2-T3SS, the molecular function and contribution to intracellular live is only known for a few of these proteins. Intracellular Salmonella modify basic functions of the host cell such as the structure of the microtubule cytoskeleton and induce a massive reorganization of vesicular transport and the endosomal system. Unique phenomena are the SPI2-dependent induction of extensive tubular membrane aggregations of endosomal or Golgi-derived vesicles. The SCV itself has features of a novel organelle and the fate of this compartment is controlled by the pathogen. Previous observations indicated that the SCV is arrested in the state of late endosomal compartment, but recent studies using advanced ultrastructural analyses and live cell studies indicate a complex and highly dynamic interaction of the intracellular Salmonella and their host cells.
Further reading: Salmonella: From Genome to Function
from Roopa Rajashekar and Michael Hensel writing in Salmonella: From Genome to Function
Salmonella enterica is a facultative intracellular pathogen that resides in a unique membrane-bound compartment, referred to as Salmonella-containing vacuole or SCV. Within the SCV, Salmonella is able to survive the antimicrobial activities of phagocytic cells and can rapidly multiply in a variety of host cells. Intracellular life of Salmonella is dependent on a large number of virulence traits, but the function of the type III secretion system (T3SS) encoded by Salmonella Pathogenicity Island 2 (SPI2) is of central importance. Although more than 20 effector proteins have been identified as translocated by the SPI2-T3SS, the molecular function and contribution to intracellular live is only known for a few of these proteins. Intracellular Salmonella modify basic functions of the host cell such as the structure of the microtubule cytoskeleton and induce a massive reorganization of vesicular transport and the endosomal system. Unique phenomena are the SPI2-dependent induction of extensive tubular membrane aggregations of endosomal or Golgi-derived vesicles. The SCV itself has features of a novel organelle and the fate of this compartment is controlled by the pathogen. Previous observations indicated that the SCV is arrested in the state of late endosomal compartment, but recent studies using advanced ultrastructural analyses and live cell studies indicate a complex and highly dynamic interaction of the intracellular Salmonella and their host cells.
Further reading: Salmonella: From Genome to Function
Salmonella virulence factors
Salmonella secreted virulence factors
from Fred Heffron, George Niemann, Hyunjin Yoon, Afshan Kidwai, Roslyn Brown, Jason McDermott, Richard Smith and Joshua Adkins writing in Salmonella: From Genome to Function
Research in the past twenty years has shown that Salmonella precisely manipulates their host by hierarchical secretion of virulence factors (effectors). More than 40 secreted virulence factors have been identified in Salmonella, but the function and mammalian targets of only a few are known. Effectors are directed to specific sub-cellular compartments and mammalian targets, and they mediate a diverse array of activities. Thus, the first half of this review focuses upon our understanding of effector mechanisms and their roles during infection.
However, the known effector repertoire is incomplete and the second half of this review places an emphasis on discovery. Computer analysis identified common secretion motifs and predicted that as many as 300 additional proteins may be secreted by Salmonella. In fact, mass spectrometry analysis identified a more complete secretome and found many novel, uncharacterized effector proteins. Several effectors identified in this study were small proteins of only 30-100 amino acids in length, suggesting that they are not enzymes but agonists or antagonists of specific host factors. One surprise from the mass spectrometry analysis was the identification of proteins that are secreted to mammalian cells via outer membrane vesicles. Complete characterization of the bewildering array of secreted proteins will take many years.
Further reading: Salmonella: From Genome to Function | Bacterial Secreted Proteins
from Fred Heffron, George Niemann, Hyunjin Yoon, Afshan Kidwai, Roslyn Brown, Jason McDermott, Richard Smith and Joshua Adkins writing in Salmonella: From Genome to Function
Research in the past twenty years has shown that Salmonella precisely manipulates their host by hierarchical secretion of virulence factors (effectors). More than 40 secreted virulence factors have been identified in Salmonella, but the function and mammalian targets of only a few are known. Effectors are directed to specific sub-cellular compartments and mammalian targets, and they mediate a diverse array of activities. Thus, the first half of this review focuses upon our understanding of effector mechanisms and their roles during infection.
However, the known effector repertoire is incomplete and the second half of this review places an emphasis on discovery. Computer analysis identified common secretion motifs and predicted that as many as 300 additional proteins may be secreted by Salmonella. In fact, mass spectrometry analysis identified a more complete secretome and found many novel, uncharacterized effector proteins. Several effectors identified in this study were small proteins of only 30-100 amino acids in length, suggesting that they are not enzymes but agonists or antagonists of specific host factors. One surprise from the mass spectrometry analysis was the identification of proteins that are secreted to mammalian cells via outer membrane vesicles. Complete characterization of the bewildering array of secreted proteins will take many years.
Further reading: Salmonella: From Genome to Function | Bacterial Secreted Proteins
Fimbriae of Salmonella
Fimbrial signature arrangements in Salmonella
from Sean-Paul Nuccio, Nicholas R. Thomson, Maria C. Fookes and Andreas J. Bäumler writing in Salmonella: From Genome to Function
The complement of fimbrial operons held within a genome represents one of the key differentiating features of the sequenced Salmonella serovars and one of the single largest sources of genetic diversity. Generically described as filamentous non-flagellar surface appendages, fimbriae (also known as pili) typically imbue an adhesive trait to the cells expressing them. While much is known about the general biology of fimbrial assembly mechanisms, the role of these structures in Salmonella pathogenesis remains poorly characterized. Here we present fimbrial operon data gathered from the seventeen completed Salmonella genome sequences and discuss its implications in Salmonella pathogenesis and dissemination.
Further reading: Salmonella: From Genome to Function | Pili and Flagella
from Sean-Paul Nuccio, Nicholas R. Thomson, Maria C. Fookes and Andreas J. Bäumler writing in Salmonella: From Genome to Function
The complement of fimbrial operons held within a genome represents one of the key differentiating features of the sequenced Salmonella serovars and one of the single largest sources of genetic diversity. Generically described as filamentous non-flagellar surface appendages, fimbriae (also known as pili) typically imbue an adhesive trait to the cells expressing them. While much is known about the general biology of fimbrial assembly mechanisms, the role of these structures in Salmonella pathogenesis remains poorly characterized. Here we present fimbrial operon data gathered from the seventeen completed Salmonella genome sequences and discuss its implications in Salmonella pathogenesis and dissemination.
Further reading: Salmonella: From Genome to Function | Pili and Flagella
Genomics and Pathogenesis of Salmonella
Genomics and Pathogenesis of Salmonella enterica serovars Typhi and Paratyphi A
from Kathryn E Holt, Tim T Perkins, Gordon Dougan and Robert A Kingsley writing in Salmonella: From Genome to Function
The genomics era has transformed the way that we can study bacterial pathogens. The availability of two complete and 17 draft genomes of S. Typhi has made it possible to study the phylogenetic structure of this pathogen in unparalleled resolution, monitor gene flux, accumulation of pseudogenes, neutral mutations and loci under selective pressure. We describe the molecular basis of Salmonella Typhi pathogenesis, in particular where genomics has contributed to our understanding in the past decade. Potentially important S. Typhi-specific virulence determinants include the Vi polysaccharide capsule, the type IV pilus, and a unique repertoire of fimbria. These may account for key differences in the disease outcome of this pathogen compared with non-typhoidal serotypes. Genome comparison with the closely related serotype S. Paratyphi A identifies a core set of pseudogenes, some of which emerged independently, that may define important features of genome degradation associated with host restriction and pathogenesis of invasive disease. Geo-phylogenetics of S. Typhi constructed from single nucleotide polymorphism data from high throughput draft genome sequences is now being applied to study molecular epidemiology in the field.
Further reading: Salmonella: From Genome to Function
from Kathryn E Holt, Tim T Perkins, Gordon Dougan and Robert A Kingsley writing in Salmonella: From Genome to Function
The genomics era has transformed the way that we can study bacterial pathogens. The availability of two complete and 17 draft genomes of S. Typhi has made it possible to study the phylogenetic structure of this pathogen in unparalleled resolution, monitor gene flux, accumulation of pseudogenes, neutral mutations and loci under selective pressure. We describe the molecular basis of Salmonella Typhi pathogenesis, in particular where genomics has contributed to our understanding in the past decade. Potentially important S. Typhi-specific virulence determinants include the Vi polysaccharide capsule, the type IV pilus, and a unique repertoire of fimbria. These may account for key differences in the disease outcome of this pathogen compared with non-typhoidal serotypes. Genome comparison with the closely related serotype S. Paratyphi A identifies a core set of pseudogenes, some of which emerged independently, that may define important features of genome degradation associated with host restriction and pathogenesis of invasive disease. Geo-phylogenetics of S. Typhi constructed from single nucleotide polymorphism data from high throughput draft genome sequences is now being applied to study molecular epidemiology in the field.
Further reading: Salmonella: From Genome to Function
Salmonella evolution
Evolutionary trends associated with niche specialization as modeled by whole genome analysis of egg-contaminating Salmonella enterica serovar Enteritidis
from Jean Guard, Devendra Shah, Cesar A. Morales and Doug Call writing in Salmonella: From Genome to Function
The mosaic nature of the Salmonella enterica genome facilitates its access to multiple environments. Many large scale genomic events have been described that contribute to the combinatorial complexity of the pathogenic Salmonellae. However, the impact of small scale genetic change occurring at the level of single nucleotide polymorphism (SNP) on the emergence of niche specialization is just now becoming appreciated. A recent review describes concepts behind the evolution that culminated in the remarkable ability of Salmonella enterica serovar Enteritidis to contaminate and survive in the internal content of eggs produced by otherwise healthy hens. Evidence suggests that combinations of SNPs facilitate niche specialization by Salmonella enterica. However, few typing methods incorporate unbiased strategies for their detection. Selection of appropriate biological assays for ranking SNPs and combinations of SNPs for their impact on the ability of Salmonella enterica to propagate outbreaks, pandemics and disease will be a significant challenge to improve the safety of the food supply.
Further reading: Salmonella: From Genome to Function
from Jean Guard, Devendra Shah, Cesar A. Morales and Doug Call writing in Salmonella: From Genome to Function
The mosaic nature of the Salmonella enterica genome facilitates its access to multiple environments. Many large scale genomic events have been described that contribute to the combinatorial complexity of the pathogenic Salmonellae. However, the impact of small scale genetic change occurring at the level of single nucleotide polymorphism (SNP) on the emergence of niche specialization is just now becoming appreciated. A recent review describes concepts behind the evolution that culminated in the remarkable ability of Salmonella enterica serovar Enteritidis to contaminate and survive in the internal content of eggs produced by otherwise healthy hens. Evidence suggests that combinations of SNPs facilitate niche specialization by Salmonella enterica. However, few typing methods incorporate unbiased strategies for their detection. Selection of appropriate biological assays for ranking SNPs and combinations of SNPs for their impact on the ability of Salmonella enterica to propagate outbreaks, pandemics and disease will be a significant challenge to improve the safety of the food supply.
Further reading: Salmonella: From Genome to Function
Salmonella survival
High-throughput screening to determine the genetic requirements for Salmonella survival under different growth conditions
from Mollie Megan Reynolds, Rocio Canals, Michael McClelland and Helene Andrews-Polymenis writing in Salmonella: From Genome to Function
Salmonella species are capable of survival in a wide range of niches, both in the environment and in an infected host. Genetic requirements for survival of Salmonella in different niches have traditionally been identified using gene expression and forward genetics. The availability of complete genome sequences, microarray technology, and cost-effective new sequencing capabilities enabled increasingly efficient high-throughput analyses of Salmonella genomes to identify elements that contribute to survival in these niches. A recent review describes many of the high-throughput tools that have been developed over the past two decades, and the genetic requirements for Salmonella survival that have been identified using these techniques.
Further reading: Salmonella: From Genome to Function
from Mollie Megan Reynolds, Rocio Canals, Michael McClelland and Helene Andrews-Polymenis writing in Salmonella: From Genome to Function
Salmonella species are capable of survival in a wide range of niches, both in the environment and in an infected host. Genetic requirements for survival of Salmonella in different niches have traditionally been identified using gene expression and forward genetics. The availability of complete genome sequences, microarray technology, and cost-effective new sequencing capabilities enabled increasingly efficient high-throughput analyses of Salmonella genomes to identify elements that contribute to survival in these niches. A recent review describes many of the high-throughput tools that have been developed over the past two decades, and the genetic requirements for Salmonella survival that have been identified using these techniques.
Further reading: Salmonella: From Genome to Function
Salmonella genomes
Comparison of Salmonella genomes
from Ye Feng, Wei-Qiao Liu, Kenneth E. Sanderson, and Shu-Lin Liu writing in Salmonella: From Genome to Function:
Salmonella contains over 2600 known lineages, each with distinct biological characteristics, including differences in the niche in which they dwell and the nature of diseases they may cause in their hosts. Genomic sequence analysis is beginning to reveal the genetic basis that determines the phenotypic differences among them. Comparison of eight sequenced genomes of Salmonella subgroup I lineages, which infect warm-blooded animals including humans, demonstrates that these pathogens share about 90% of their genes (the "core" genome), with the remaining ca. 10% genes being unique to each of the lineages (the "accessory" genome). Prophages and Salmonella Pathogenicity Islands (SPIs) are the main components of the accessory genome. Insertion of large DNA segments, such as SPI7 in S. Typhi, may disrupt physical balance of the genome between replication origin and terminus and rearrangements of the genome, such as inversions or translocations mediated by homologous sites (rrn operons, prophages, IS200, etc.) may accelerate rebalancing of the genome. Laterally transferred genes are the main driving force in Salmonella evolution and speciation; evidence exists indicating that mismatch repair genes may spontaneously regulate bacterial mutability through allele conversion to facilitate or inhibit incorporation of foreign DNA. Further studies may help elucidate the genetic basis of distinct pathogeneses and host ranges among the Salmonella pathogens.
Further reading: Salmonella: From Genome to Function
from Ye Feng, Wei-Qiao Liu, Kenneth E. Sanderson, and Shu-Lin Liu writing in Salmonella: From Genome to Function:
Salmonella contains over 2600 known lineages, each with distinct biological characteristics, including differences in the niche in which they dwell and the nature of diseases they may cause in their hosts. Genomic sequence analysis is beginning to reveal the genetic basis that determines the phenotypic differences among them. Comparison of eight sequenced genomes of Salmonella subgroup I lineages, which infect warm-blooded animals including humans, demonstrates that these pathogens share about 90% of their genes (the "core" genome), with the remaining ca. 10% genes being unique to each of the lineages (the "accessory" genome). Prophages and Salmonella Pathogenicity Islands (SPIs) are the main components of the accessory genome. Insertion of large DNA segments, such as SPI7 in S. Typhi, may disrupt physical balance of the genome between replication origin and terminus and rearrangements of the genome, such as inversions or translocations mediated by homologous sites (rrn operons, prophages, IS200, etc.) may accelerate rebalancing of the genome. Laterally transferred genes are the main driving force in Salmonella evolution and speciation; evidence exists indicating that mismatch repair genes may spontaneously regulate bacterial mutability through allele conversion to facilitate or inhibit incorporation of foreign DNA. Further studies may help elucidate the genetic basis of distinct pathogeneses and host ranges among the Salmonella pathogens.
Further reading: Salmonella: From Genome to Function
Phages of Salmonella
Typing phages and prophages of Salmonella
from Wolfgang Rabsch, Sandra Truepschuch, Daniel Windhorst and Roman G. Gerlach writing in Salmonella: From Genome to Function:
Most Salmonella strains contain prophages or remnant phages and release them spontaneously. Special bacteriophages were developed and used in phage typing systems for epidemiological work all over the world since 1947 to control salmonellosis. This method provides fast and inexpensive characterization of frequent serovars such as S. Typhimurium or S. Typhi on the sub-serovar level and is especially useful for primary analysis before investigation by other, more expensive molecular techniques such as sequencing. Prophages are themselves not only variable elements in a chromosome but also variable by module exchange within the prophage genome, thus providing a high discriminating power. The availability of several genome sequences of different Salmonella serovars has recently led to the identification of new prophage-like elements. The prophages present in serovars Typhimurium, Enteritidis and Typhi are discussed. Salmonella phages frequently carry foreign DNA, so called morons. These morons are not necessary for phage functions but provide a benefit for the host. A list of some new morons found in different Salmonella serovars is presented. Recently, a monophasic variant of S. Typhimurium mainly belonging to Anderson phage type DT193 has become one of the dominant causes of salmonellosis in Germany and other European countries. These strains with the antigenic formula 4,[5],12:i:- do not express the 2nd phase flagellum. Investigation of their prophage attachment sites showed that the sites for Gifsy-1, Gifsy-2 and ST64B were occupied by the respective prophages. In about 90% of the monophasic DT193 strains the P22/ST64T attachment site was occupied by a novel 18.4 kb fragment, containing several open reading frames with significant similiarity to phage-related genes.
Further reading: Salmonella: From Genome to Function | Bacteriophage: Genetics and Molecular Biology
from Wolfgang Rabsch, Sandra Truepschuch, Daniel Windhorst and Roman G. Gerlach writing in Salmonella: From Genome to Function:
Most Salmonella strains contain prophages or remnant phages and release them spontaneously. Special bacteriophages were developed and used in phage typing systems for epidemiological work all over the world since 1947 to control salmonellosis. This method provides fast and inexpensive characterization of frequent serovars such as S. Typhimurium or S. Typhi on the sub-serovar level and is especially useful for primary analysis before investigation by other, more expensive molecular techniques such as sequencing. Prophages are themselves not only variable elements in a chromosome but also variable by module exchange within the prophage genome, thus providing a high discriminating power. The availability of several genome sequences of different Salmonella serovars has recently led to the identification of new prophage-like elements. The prophages present in serovars Typhimurium, Enteritidis and Typhi are discussed. Salmonella phages frequently carry foreign DNA, so called morons. These morons are not necessary for phage functions but provide a benefit for the host. A list of some new morons found in different Salmonella serovars is presented. Recently, a monophasic variant of S. Typhimurium mainly belonging to Anderson phage type DT193 has become one of the dominant causes of salmonellosis in Germany and other European countries. These strains with the antigenic formula 4,[5],12:i:- do not express the 2nd phase flagellum. Investigation of their prophage attachment sites showed that the sites for Gifsy-1, Gifsy-2 and ST64B were occupied by the respective prophages. In about 90% of the monophasic DT193 strains the P22/ST64T attachment site was occupied by a novel 18.4 kb fragment, containing several open reading frames with significant similiarity to phage-related genes.
Further reading: Salmonella: From Genome to Function | Bacteriophage: Genetics and Molecular Biology
Salmonella classification
New approaches in sub-species level Salmonella classification
from Burkhard Malorny, Elisabeth Hauser and Ralf Dieckmann writing in Salmonella: From Genome to Function:
Salmonellae form a complex group of bacteria consisting of two species, 6 subspecies and more than 2,500 serovars (serotypes). Salmonella identification below species level is most often limited to phenotypic typing methods such as biochemical and serological identification, which are costly, time-consuming and do not always reflect the evolution of Salmonella groups. Newer methods for Salmonella typing and subtyping include genome-based methods such as pulsed field gel electrophoresis (PFGE), Multiple Loci VNTR Analysis (MLVA), Multilocus sequence typing (MLST) and (multiplex-) PCR-based methods. In the last years further molecular typing technologies were evaluated for this purpose. A recent review discusses some of these emerging technologies and gives an outlook on future developments with a focus on oligonucleotide microarrays, spectroscopic methods such as MALDI-TOF mass spectrometry and special developments such as bead-based suspension arrays using Luminex technology and DNA sequence-based approaches. These new techniques promise significant advantages compared to traditional culture-based methods with respect to speed, ease of use, reliability and automation.
Further reading: Salmonella: From Genome to Function
from Burkhard Malorny, Elisabeth Hauser and Ralf Dieckmann writing in Salmonella: From Genome to Function:
Salmonellae form a complex group of bacteria consisting of two species, 6 subspecies and more than 2,500 serovars (serotypes). Salmonella identification below species level is most often limited to phenotypic typing methods such as biochemical and serological identification, which are costly, time-consuming and do not always reflect the evolution of Salmonella groups. Newer methods for Salmonella typing and subtyping include genome-based methods such as pulsed field gel electrophoresis (PFGE), Multiple Loci VNTR Analysis (MLVA), Multilocus sequence typing (MLST) and (multiplex-) PCR-based methods. In the last years further molecular typing technologies were evaluated for this purpose. A recent review discusses some of these emerging technologies and gives an outlook on future developments with a focus on oligonucleotide microarrays, spectroscopic methods such as MALDI-TOF mass spectrometry and special developments such as bead-based suspension arrays using Luminex technology and DNA sequence-based approaches. These new techniques promise significant advantages compared to traditional culture-based methods with respect to speed, ease of use, reliability and automation.
Further reading: Salmonella: From Genome to Function