Horizontal gene transfer of a ColV plasmid has resulted in a dominant avian clonal type of Salmonella enterica serovar Kentucky

Salmonella Biomapping of a Commercial Broiler Hatchery

Poultry-associated salmonellosis results in significant costs to poultry producers and consumers. Given the vertically integrated nature of the United States poultry industry, a better understanding of Salmonella ecology throughout all levels of poultry production is essential. One nexus point is the hatchery, where eggs from multiple broiler breeder farms are incubated and hatched, with the chicks being sent to numerous farms; therefore, the hatchery represents an ideal area to understand preharvest Salmonella ecology and flow. To achieve this, a commercial broiler hatchery was biomapped, focusing on Salmonella prevalence and serotype diversity among four major sample type categories (Air, Egg, Water, Facility) across five different places in the prehatch, hatch, and posthatch areas. Following two sets of eggs from broiler breeder farms over two production days, the overall Salmonella prevalence was 26% (48/184). Of the positive samples, the highest prevalence was observed in swabs taken from the floor drains in the facility and transport truck (56%), as well as in the hatch and posthatch hatchery areas (50%). Kentucky (n = 17), Gaminara (n = 12), and Alachua (n = 11) were the dominant Salmonella serotypes, with serotypes of greatest outbreak concern from chickens (Enteritidis) representing only 6.25% (3/48) of all recovered Salmonella isolates. The posthatch transport area, including the underfloor reservoirs of the transport trucks, not only harbored Enteritidis but also the enrichment broths from these Salmonella-positive samples also possessed sequences matching the commercial live-attenuated vaccine Typhimurium strain according to CRISPR SeroSeq analyses. These findings highlight the complex diversity of commercial hatchery Salmonella populations, including identifying facility floor drains and transport trucks as potentially important critical control points for hatchery managers to focus their Salmonella mitigation efforts to reduce loads and serotypes entering live production farms.

Prevalence, antimicrobial resistance and genomic comparison of non-typhoidal salmonella isolated from pig farms with different levels of intensification in Yangon Region, Myanmar

In Myanmar, where backyard, semi-intensive, and intensive pig (Sus scrofa domesticus) farming coexist, there is limited understanding of the zoonotic risks and antimicrobial resistance (AMR) associated with these farming practices. This study was conducted to investigate the prevalence, AMR and genomic features of Salmonella in pig farms in the Yangon region and the impact of farm intensification to provide evidence to support risk-based future management approaches. Twenty-three farms with different production scales were sampled for two periods with three sampling-visit each. Antimicrobial susceptibility tests and whole-genome sequencing were performed on the isolates. The prevalence of Salmonella was 44.5% in samples collected from backyard farms, followed by intensive (39.5%) and semi-intensive farms (19.5%). The prevalence of multi-drug resistant isolates from intensive farms (45/84, 53.6%) was higher than those from backyard (32/171, 18.7%) and semi-intensive farms (25/161, 15.5%). Among 28 different serovars identified, S. Weltevreden (40; 14.5%), S. Kentucky (38; 13.8%), S. Stanley (35, 12.7%), S. Typhimurium (22; 8.0%) and S. Brancaster (20; 7.3%) were the most prevalent serovars and accounted for 56.3% of the genome sequenced strains. The diversity of Salmonella serovars was highest in semi-intensive and backyard farms (21 and 19 different serovars, respectively). The high prevalence of globally emerging S. Kentucky ST198 was detected on backyard farms. The invasive-infection linked typhoid-toxin gene (cdtB) was found in the backyard farm isolated S. Typhimurium, relatively enriched in virulence and AMR genes, presented an important target for future surveillance. While intensification, in terms of semi-intensive versus backyard production, maybe a mitigator for zoonotic risk through a lower prevalence of Salmonella, intensive production appears to enhance AMR-associated risks. Therefore, it remains crucial to closely monitor the AMR and virulence potential of this pathogen at all scales of production. The results underscored the complex relationship between intensification of animal production and the prevalence, diversity and AMR of Salmonella from pig farms in Myanmar.

Genomics Characterization of Colistin Resistant Escherichia coli from Chicken Meat-the First Report in the United Arab Emirates

Plasmid-mediated colistin resistance is an emerging One Health challenge at the human-food-environment interface. In this study, 12 colistin-resistant Escherichia coli carrying mcr-1.1 gene were characterized using whole-genome sequencing. This is the first report from locally produced chicken meat in the United Arab Emirates. The characterized isolates harbored virulence-associated factors ranging from 4 to 17 genes per isolate. The multilocus sequence type 1011 was identified in 5 (41.6%) isolates. Six (50.0%) of the isolates harbored blaCTX-M-55. All of the E. coli isolates contained Incl2 plasmids. This study highlights for the first time chicken meat as a potential reservoir of mcr-1.1 carrying E. coli in the UAE. This study has implications for food safety and underscores the need for comprehensive surveillance strategies to monitor the spread of colistin resistance. Results presented in this short communication address knowledge gaps on the epidemiology of plasmid-mediated colistin resistance in the Middle East food production chain.

Effects of in ovo injection of bacterial peptides and CpG-ODN on Salmonella enterica serovar Heidelberg infection in specific pathogen-free (SPF) chicks

RESEARCH HIGHLIGHTS

Peptides + CpG-ODN reduced SH in caeca at the first week post-infection.Administered formulations did not reduce SH-faecal excretion.Levels of intestinal IgA were similar between all groups.CpG-ODN improved some parameters associated with chick intestinal health.

Genetic relatedness and virulence potential of Salmonella Schwarzengrund strains with or without an IncFIB-IncFIC(FII) fusion plasmid isolated from food and clinical sources

A total of 55 food and clinical S. Schwarzengrund isolates were assayed for plasmid content, among which an IncFIB-IncFIC(FII) fusion plasmid, conferring streptomycin resistance, was detected in 17 isolates. Among the 17 isolates, 9 were food isolates primarily collected from poultry meat, and 8 clinical isolates collected from stool, urine, and gallbladder. SNP-based phylogenetic analyses showed that the isolates carrying the fusion plasmid formed a subclade indicating the plasmid was acquired and is now maintained by the lineage. Phylogenetic analysis of the plasmid suggested it is derived from avian pathogenic plasmids and might confer an adaptive advantage to the S. Schwarzengrund isolates within birds. IncFIB-IncFIC(FII) fusion plasmids from all food and three clinical isolates were self-conjugative and successfully transferred into E. coli J53 by conjugation. Food and clinical isolates had similar virulome profiles and were able to invade human Caco-2 cells. However, the IncFIB-IncFIC(FII) plasmid did not significantly add to their invasion and persistence potential in human Caco-2 cells.

Genomic Insights into the First Emergence of blaNDM-5-Carrying Carbapenem-Resistant Salmonella enterica Serovar London Strain in China

Carbapenem-resistant Salmonella enterica (S. enterica) pose a significant threat to public health, causing gastroenteritis and invasive infections. We report the first emergence of a carbapenem-resistant S. enterica serovar London strain, A132, carrying the blaNDM-5 gene in China. Whole-genome sequencing and bioinformatics analysis assigned A132 to be ST155, a multidrug-resistant clone frequently reported in China. The strain A132 exhibited resistance to multiple antibiotics, with 20 acquired antibiotic resistance genes (ARGs) identified, predominantly located on the IncFIB plasmid (pA132-1-NDM). Notably, the blaNDM-5 gene was located within an IS26 flanked-class 1 integron-ISCR1 complex, comprising two genetic cassettes. One cassette is the class 1 integron, which may facilitate the transmission of the entire complex, while the other is the blaNDM-5-containing ISCR1-IS26-flanked cassette, carrying multiple other ARGs. Genbank database search based on the blaNDM-5-carrying cassette identified a similar genetic context found in transmissible IncFIA plasmids from Escherichia coli (p91) and Enterobacter hormaechei (p388) with a shared host range, suggesting the potential for cross-species transmission of blaNDM-5. To our knowledge, this is the first reported case of Salmonella serovar London ST155 harboring blaNDM-5 gene. Phylogenetic analysis indicated a close relationship between A132 and eight S. London ST155 strains isolated from the same province. However, A132 differed by carrying the blaNDM-5 gene and four unique ARGs. Given the high transmissibility of the F-type plasmid harboring blaNDM-5 and 18 other ARGs, it is imperative to implement vigilant surveillance and adopt appropriate infection control measures to mitigate the threat to public health.

Revisiting the Multifaceted Roles of Bacteriocins : The Multifaceted Roles of Bacteriocins

Bacteriocins are gene-encoded antimicrobial peptides produced by bacteria. These peptides are heterogeneous in terms of structure, antimicrobial activities, biosynthetic clusters, and regulatory mechanisms. Bacteriocins are widespread in nature and may contribute to microbial diversity due to their capacity to target specific bacteria. Primarily studied as food preservatives and therapeutic agents, their function in natural settings is however less known. This review emphasizes the ecological significance of bacteriocins as multifunctional peptides by exploring bacteriocin distribution, mobility, and their impact on bacterial population dynamics and biofilms.

Epidemiology of Salmonella enterica subspecies enterica serotypes, isolated from imported, farmed and feral poultry in the Cayman Islands

Non-typhoidal Salmonellae (NTS) are common foodborne pathogens throughout the world causing acute gastroenteritis. Compared to North America and Europe, there is little information on NTS in the Caribbean. Here we investigated the prevalence and characteristics of NTS present in the local poultry of the Cayman Islands to determine the public health risk. In total, we collected 156 samples. These were made up of boot swabs of 31 broiler farms and 31 layer farms (62 samples), paper bedding from 45 imported chick boxes, and 49 pooled cecum samples from feral chickens, each sample representing 10 individual chickens. Salmonella was isolated using the ISO 6579 protocol and isolates were characterized using Whole Genome Sequencing (WGS) analysis. Eighteen Salmonella isolates were obtained and comprised six S. enterica subspecies enterica serotypes and one subspecies houtenae serotype. Serotypes were: S. Kentucky (n = 9), S. Saintpaul (n = 5), S. Javiana (n = 1), S. Senftenberg (n = 1), S. Poona (n = 1) and S. Agona (n = 1). S. Kentucky strains were all ST152 and clonally related to poultry strains from the United states. S. Saintpaul ST50 strains showed clonality to North American strains. Over half of the strains (n = 11) contained resistance genes to at least two antibiotic groups and five strains were MDR, mainly those from imported day-old chicks. The blaCMY-2 gene was found in S. Kentucky from day-old chicks. Strains from feral poultry had no acquired AMR genes. While serotypes from feral poultry have been identified in human infections, they pose minimal risk due to their low virulence.

Versatile allelic replacement and self-excising integrative vectors for plasmid genome mutation and complementation

IMPORTANCE

In spite of the dissemination of multidrug-resistant plasmids among Gram-negative pathogens, including those carrying virulence genes, vector tools for studying plasmid-born genes are lacking. The allelic replacement vectors can be used to generate plasmid or chromosomal mutations including markless point mutations. This is the first report describing a self-excising integrative vector that can be used as a stable single-copy complementing tool to study medically important pathogens including in vivo studies without the need for antibiotic selection. Overall, our newly developed vectors can be applied for the assessment of the function of plasmid-encoded genes by specifically creating mutations, moving large operons between plasmids and to/from the chromosome, and complementing phenotypes associated with gene mutation. Furthermore, the vectors express chromophores for the detection of target gene modification or colony isolation, avoiding time-consuming screening procedures.

Vaccines to Control Salmonella in Poultry

This review is focused on describing and analyzing means by which Salmonella enterica serotype strains have been genetically modified with the purpose of developing safe, efficacious vaccines to present Salmonella-induced disease in poultry and to prevent Salmonella colonization of poultry to reduce transmission through the food chain in and on eggs and poultry meat. Emphasis is on use of recently developed means to generate defined deletion mutations to eliminate genetic sequences conferring antimicrobial resistance or residual elements that might lead to genetic instability. Problems associated with prior means to develop vaccines are discussed with presentation of various means by which these problems have been lessened, if not eliminated. Practical considerations are also discussed in hope of facilitating means to move lab-proven successful vaccination procedures and vaccine candidates to the marketplace to benefit the poultry industry.

Prevalence, antibiotic susceptibility and genomic analysis of Salmonella from retail meats in Shaanxi, China

Salmonella is a major foodborne pathogen that poses a substantial risk to food safety and public health. This study aimed to assess the prevalence, antibiotic susceptibility, and genomic features of Salmonella isolates recovered from 600 retail meat samples (300 pork, 150 chicken and 150 beef) from August 2018 to October 2019 in Shaanxi, China. Overall, 40 (6.67 %) of 600 samples were positive to Salmonella, with the highest prevalence in chicken (21.33 %, 32/150), followed in pork (2.67 %, 8/300), while no Salmonella was detected in beef. A total of 10 serotypes and 11 sequence types (STs) were detected in 40 Salmonella isolates, with the most common being ST198 S. Kentucky (n = 15), ST13 S. Agona (n = 6), and ST17 S. Indiana (n = 5). Resistance was most commonly found to tetracycline (82.50 %), followed by to ampicillin (77.50 %), nalidixic acid (70.00 %), kanamycin (57.50 %), ceftriaxone (55.00 %), cefotaxime (52.50 %), cefoperazone (52.50 %), chloramphenicol (50.00 %), levofloxacin (57.50 %), cefotaxime (52.50 %), kanamycin (52.50 %), chloramphenicol (50.00 %), ciprofloxacin (50.00 %), and levofloxacin (50.00 %). All ST198 S. Kentucky isolates showed multi-drug resistance (MDR; ≥3 antimicrobial categories) pattern. Genomic analysis showed 56 distinct antibiotic resistance genes (ARGs) and 6 target gene mutations of quinolone resistance determining regions (QRDRs) in 40 Salmonella isolates, among which, the most prevalent ARG types were related to aminoglycosides and β-lactams resistance, and the most frequent mutation in QRDRs was GyrA (S83F) (47.5 %). The number of ARGs in Salmonella isolates showed a significant positive correlation with the numbers of insert sequences (ISs) and plasmid replicons. Taken together, our findings indicated retail chickens were seriously contaminated, while pork and beef are rarely contaminated by Salmonella. Antibiotic resistance determinants and genetic relationships of the isolates provide crucial data for food safety and public health safeguarding.

Clonal diversity and zoonotic potential of MDR Escherichia coli isolated from poultry at different age intervals

1. A pool of 480 E. coli isolates of poultry (broilers and ducks) representing different time intervals (0, 10, 20 and 30 days) was selected for ribotyping and used to determine polymorphism of 16-23S ribosomal RNA intergenic space. All the isolates were multidrug-resistant (MDR).2. Out of these, 10 isolates were tested for MultiLocus Sequence Typing (MLST) among which novel allelic combinations and therefore new sequence types were identified in seven isolates.3. This work showed the changes in E. coli strains structure at farm level and individual bird level in host species raised on organised farms with similar parental lineage and environmental housing. The statistical results showed that the structure of variation is very different by farm, supporting a strong effect of location, which confirms the temporal clustering.4. There were significant differences between E. coli strains in chickens and ducks, indicating host specificity of the E. coli strains.5. Some of the pathogenic E. coli strains found using MLST belonged to ST735, ST2796 and a pandemic clone ST752 of ST10 clonal complex. The results strongly suggested the clonal expansion and establishment of specific MDR clones that have zoonotic relevance.

Structural analysis of VirD4 a type IV ATPase encoded by transmissible plasmids of Salmonella enterica isolated from poultry products

Bacterial species have evolved with a wide variety of cellular devices, and they employ these devices for communication and transfer of genetic materials and toxins. They are classified into secretory system types I to VI based on their structure, composition, and functional activity. Specifically, the bacterial type IV secretory system (T4SS) is a more versatile system than the other secretory systems because it is involved in the transfer of genetic materials, proteins, and toxins to the host cells or other bacterial species. The T4SS machinery is made up of several proteins with distinct functions and forms a complex which spans the inner and outer membranes. This secretory machinery contains three ATPases that are the driving force for the functionality of this apparatus. At the initial stage of the secretion process, the selection of substrate molecules and processing occurs at the cytoplasmic region (also known as relaxosome), and then transfer mechanisms occur through the secretion complex. In this process, the VirD4 ATPase is the first molecule that initiates substrate selection, which is subsequently delivered to the secretory machinery. In the protein data bank (PDB), no structural information is available for the VirD4 ATPase to understand the functional property. In this manuscript, we have modeled VirD4 structure in the Gram-negative bacterium Salmonella enterica and described the predicted functional importance. The sequence alignment shows that VirD4 of S. enterica contains several insertion regions as compared with the template structure (pdb:1E9R) used for homology modeling. In this study, we hypothesized that the insertion regions could play a role in the flexible movement of the hexameric unit during the relaxosome processing or transfer of the substrate.

Genomic Analysis of Multidrug-Resistant Salmonella enterica Serovar Kentucky Isolates from Humans, Turkey, and Food in the Republic of Serbia

Owing to the emerging resistance to antimicrobials in Salmonella Kentucky isolates around the globe, the genomic comparison of all the registered multidrug-resistant Salmonella Kentucky isolates in Serbia (five from humans, one from turkey flock, and one from meat) was done. Most of the isolates were isolated from patients returning from Egypt or Tunisia or originated from imported turkey flock and turkey meat. The comparative analysis of resistance and virulence genes was done. All isolates belonged to sequence type-ST198 and were resistant to ciprofloxacin (Cip). The resistance to Cip was mediated by target mutations of the gyrA and parC genes, which encode topoisomerase I and II, respectively. Multidrug-resistant phenotype to aminoglycosides, β-lactam antibiotics, sulfonamides, and tetracyclines was detected in five isolates. However, none of the isolates was pan-resistant to antimicrobials. The number of single nucleotide polymorphisms between isolates varied from 8 to 43 and phylogenomics revealed the genetic proximity of the human isolate 10475/11 and the turkey meat isolate 5264/14, indicating a possible meat-to-human transfer. All isolates belonged to the main Salmonella Kentucky MDR lineage, carrying the Salmonella genomic island 1 (SGI1-K) subtype. The SGI1-K of Serbian isolates showed mosaicism attributed to rapid intraclonal evolution. Many virulence factors were detected in all the isolates, including SPI-1, SPI-2, SPI-3, SPI-4, SPI-5, SPI-9, and C63PI. Although Salmonella Kentucky has rarely been isolated from humans, food, and animals in Serbia, further surveillance is needed to diminish the risk of the spreading of resistant clones and their meat-to-human transmission.

Microcins reveal natural mechanisms of bacterial manipulation to inform therapeutic development

Microcins are an understudied and poorly characterized class of antimicrobial peptides. Despite the existence of only 15 examples, all identified from the Enterobacteriaceae, microcins display diversity in sequence, structure, target cell uptake, cytotoxic mechanism of action and target specificity. Collectively, these features describe some of the unique means nature has contrived for molecules to cross the 'impermeable' barrier of the Gram-negative bacterial outer membrane and inflict cytotoxic effects. Microcins appear to be widely dispersed among different species and in different environments, where they function in regulating microbial communities in diverse ways, including through competition. Growing evidence suggests that microcins may be adapted for therapeutic uses such as antimicrobial drugs, microbiome modulators or facilitators of peptide uptake into cells. Advancing our biological, ecological and biochemical understanding of the roles of microcins in bacterial interactions, and learning how to regulate and modify microcin activity, is essential to enable such therapeutic applications.

Genomic characterization of multidrug-resistant Salmonella serovar Kentucky ST198 isolated in poultry flocks in Spain (2011-2017)

Salmonella Kentucky is commonly found in poultry and rarely associated with human disease. However, a multidrug-resistant (MDR) S. Kentucky clone [sequence type (ST)198] has been increasingly reported globally in humans and animals. Our aim here was to assess if the recently reported increase of S. Kentucky in poultry in Spain was associated with the ST198 clone and to characterize this MDR clone and its distribution in Spain. Sixty-six isolates retrieved from turkey, laying hen and broiler in 2011–2017 were subjected to whole-genome sequencing to assess their sequence type, genetic relatedness, and presence of antimicrobial resistance genes (ARGs), plasmid replicons and virulence factors. Thirteen strains were further analysed using long-read sequencing technologies to characterize the genetic background associated with ARGs. All isolates belonged to the ST198 clone and were grouped in three clades associated with the presence of a specific point mutation in the gyrA gene, their geographical origin and isolation year. All strains carried between one and 16 ARGs whose presence correlated with the resistance phenotype to between two and eight antimicrobials. The ARGs were located in the Salmonella genomic island (SGI-1) and in some cases (bla_SHV-12, catA1, cmlA1, dfrA and multiple aminoglycoside-resistance genes) in IncHI2/IncI1 plasmids, some of which were consistently detected in different years/farms in certain regions, suggesting they could persist over time. Our results indicate that the MDR S. Kentucky ST198 is present in all investigated poultry hosts in Spain, and that certain strains also carry additional plasmid-mediated ARGs, thus increasing its potential public health significance.

A role for ColV plasmids in the evolution of pathogenic Escherichia coli ST58

Escherichia coli ST58 has recently emerged as a globally disseminated uropathogen that often progresses to sepsis. Unlike most pandemic extra-intestinal pathogenic E. coli (ExPEC), which belong to pathogenic phylogroup B2, ST58 belongs to the environmental/commensal phylogroup B1. Here, we present a pan-genomic analysis of a global collection of 752 ST58 isolates from diverse sources. We identify a large ST58 sub-lineage characterized by near ubiquitous carriage of ColV plasmids, which carry genes encoding virulence factors, and by a distinct accessory genome including genes typical of the Yersiniabactin High Pathogenicity Island. This sub-lineage includes three-quarters of all ExPEC sequences in our study and has a broad host range, although poultry and porcine sources predominate. By contrast, strains isolated from cattle often lack ColV plasmids. Our data indicate that ColV plasmid acquisition contributed to the divergence of the major ST58 sub-lineage, and different sub-lineages inhabit poultry, swine and cattle.

F Plasmid Lineages in Escherichia coli ST95: Implications for Host Range, Antibiotic Resistance, and Zoonoses

Escherichia coli sequence type 95 (ST95) is an extraintestinal pathogenic E. coli (ExPEC) renowned for its ability to cause significant morbidity and mortality in humans and poultry. A core genome analysis of 668 ST95 isolates generated 10 clades (A to J), 5 of which are reported here for the first time. F plasmid replicon sequence typing showed that almost a third (178/668 [27%]) of the collection carry pUTI89 (F29:B10) and were restricted to clade A and a sublineage of clade B. In contrast, almost half (328/668 [49%]) of the collection across multiple clades harbor ColV plasmids (multiple F types). Strikingly, ST95 lineages with pUTI89 were almost exclusively from humans, while ColV⁺ ST95 lineages were sourced from poultry and humans. Clade I was notable because it comprises temporally and geographically matched ColV⁺ isolates sourced from human and retail poultry meat, suggesting interspecies transmission via food. Clade F contained ST95 isolates of bovine origin, none of which carried ColV or pUTI89 plasmids. Remarkably, an analysis of a cohort of 34,176 E. coli isolates comprising 2,570 sequence types mirrored what was observed in ST95: (i) pUTI89 was overwhelmingly linked to E. coli sourced from humans but almost entirely absent from 13,027 E. coli isolates recovered from poultry, pigs, and cattle, and (ii) E. coli isolates harboring ColV plasmids were from multiple sources, including humans, poultry, and swine. Overall, our data suggest that F plasmids influence E. coli host range, clade structure, and zoonotic potential in ST95 and ExPEC more broadly.

IMPORTANCEE. coli ST95 is one of five dominant ExPEC lineages globally and noted for causing urinary tract and bloodstream infections and neonatal meningitis in humans and colibacillosis in poultry. Using high-resolution phylogenomics, we show that F replicon sequence type is linked to ST95 clade structure and zoonotic potential. Specifically, human centric ST95 clades overwhelmingly harbor F29:B10 (pUTI89) plasmids, while clades carrying both human- and poultry-sourced isolates are typically ColV⁺ with multiple replicon types. Importantly, several clades identified clonal ColV⁺ ST95 isolates from human and poultry sources, but clade I, which housed temporally and spatially matched isolates, provided the most robust evidence. Notably, patterns of association of F replicon types with E. coli host were mirrored within a diverse collection of 34,176 E. coli genomes. Our studies indicate that the role of food animals as a source of human ExPEC disease is complex and warrants further investigation.

Comparison of Reference-Based Assembly and De Novo Assembly for Bacterial Plasmid Reconstruction and AMR Gene Localization in Salmonella enterica Serovar Schwarzengrund Isolates

It is well established that plasmids carrying multiple antimicrobial resistance (AMR) genes can be easily transferred among bacterial isolates by horizontal gene transfer. Previous studies have shown that a combination of short- and long-read approaches is effective in reconstructing accurate plasmids. However, high-quality Illumina short reads mapped onto the long reads in the context of an AMR hybrid monitoring strategy have not yet been explored. Hence, this study aimed to improve the reconstruction of plasmids, including the localization of AMR genes, using the above-described parameters on whole-genome sequencing (WGS) results. To the best of our knowledge, this study is the first to use S1 nuclease pulsed-field gel electrophoresis (S1-PFGE) to confirm the number and sizes of plasmids detected by in silico-based predictions in Salmonella strains. Our results showed that de novo assembly did not detect the number of bacterial plasmids more accurately than reference-based assembly did. As this new hybrid mapping strategy surpassed de novo assembly in bacterial reconstruction, it was further used to identify the presence and genomic location of AMR genes among three Salmonella enterica serovar Schwarzengrund isolates. The AMR genes identified in the bacterial chromosome among the three Salmonella enterica serovar Schwarzengrund isolates included: AAC(3)-IV, AAC(6')-Iy, aadA2, APH(4)-Ia, cmlA1, golS, mdsA, mdsB, mdsC, mdtK, qacH, sdiA, sul2, sul3, and TEM-1 genes. Moreover, the presence of TEM-1, AAC(3)-IV, aadA2, APH(4)-Ia, cmlA1, dfrA12, floR, sul1, sul3, and tet(A) genes found within three IncFIB plasmids and one IncX1 plasmid highlight their possible transmission into the environment, which is a public health risk. In conclusion, the generated data using this new hybrid mapping strategy will contribute to the improvement of AMR monitoring and support the risk assessment of AMR dissemination.

Salmonella Genomics in Public Health and Food Safety

The species Salmonella enterica comprises over 2,600 serovars, many of which are known to be intracellular pathogens of mammals, birds, and reptiles. It is now apparent that Salmonella is a highly adapted environmental microbe and can readily persist in a number of environmental niches, including water, soil, and various plant (including produce) species. Much of what is known about the evolution and diversity of nontyphoidal Salmonella serovars (NTS) in the environment is the result of the rise of the genomics era in enteric microbiology. There are over 340,000 Salmonella genomes available in public databases. This extraordinary breadth of genomic diversity now available for the species, coupled with widespread availability and affordability of whole-genome sequencing (WGS) instrumentation, has transformed the way in which we detect, differentiate, and characterize Salmonella enterica strains in a timely way. Not only have WGS data afforded a detailed and global examination of the molecular epidemiological movement of Salmonella from diverse environmental reservoirs into human and animal hosts, but they have also allowed considerable consolidation of the diagnostic effort required to test for various phenotypes important to the characterization of Salmonella. For example, drug resistance, serovar, virulence determinants, and other genome-based attributes can all be discerned using a genome sequence. Finally, genomic analysis, in conjunction with functional and phenotypic approaches, is beginning to provide new insights into the precise adaptive changes that permit persistence of NTS in so many diverse and challenging environmental niches.

Prevalence of IncFIB Plasmids Found among Salmonella enterica Serovar Schwarzengrund Isolates from Animal Sources in Taiwan Using Whole-Genome Sequencing

Salmonella enterica serovar Schwarzengrund is one of the most frequently isolated Salmonella serotypes responsible for human and poultry infections in Taiwan, and it has raised public health concerns. To better facilitate the understanding of transmission patterns and the dynamics of epidemics, sharing molecular data on pathogen profiles is urgently needed. The objectives of the current study were to determine and establish baseline data of S. enterica serovar Schwarzengrund isolates from 23 epidemiologically unrelated sources from year 2000 to 2018 and examine their phenotypic and genotypic characteristics. Genomic DNA of the Salmonella isolates was extracted and subjected to whole-genome sequencing using an Illumina platform. Results showed that all selected isolates exhibited multidrug resistance, and six of those were resistant to ciprofloxacin phenotypically. Genotypically, these isolates carried genes resistant to aminoglycoside (100%), phenicol (91.3%), β-lactams (69.5%), folate pathway antagonist (100%), tetracycline (82.6%), and fluoroquinolone (4.3%). Moreover, these isolates harbor integrons with five different gene cassettes identified for the first time, which are associated with resistance to trimethoprim, streptomycin, tetracycline, sulfonamide, chloramphenicol, and gentamicin. Furthermore, prevalence of IncFIB plasmid was found among studied isolates, which may increase its ability to colonize the chicken cecum and cause extra-intestinal disease. Salmonella pathogenicity islands SPI-1 to SPI-5, SPI-13, and SPI-14, as well as C63PI locus, were also detected in all isolates. This study demonstrated that a considerable high antimicrobial resistance with high virulence levels of Salmonella were found from animal sources. Sharing data on these pathogen profiles can not only help increase the reproducibility and accessibility of genomic analysis but can also support surveillance and epidemiological investigations for salmonellosis in the region.

High-Resolution Comparative Genomics of Salmonella Kentucky Aids Source Tracing and Detection of ST198 and ST152 Lineage-Specific Mutations

Non-typhoidal Salmonella (NTS) is a major cause of foodborne illness globally. Salmonella Kentucky is a polyphyletic NTS serovar comprised of two predominant multilocus sequence types (STs): ST152 and ST198. Epidemiological studies have revealed that ST152 is most prevalent in US poultry whereas ST198 is more prevalent in international poultry. Interestingly, ST152 is sporadically associated with human illness, whereas ST198 is more commonly associated with human disease. The goal of this study was to develop a better understanding of the epidemiology of ST198 and ST152 in WA State. We compared the antimicrobial resistance phenotypes and genetic relationship, using pulsed-field gel electrophoresis, of 26 clinical strains of S. Kentucky isolated in Washington State between 2004 and 2014, and 140 poultry-associated strains of S. Kentucky mostly recovered from the northwestern USA between 2004 and 2014. We also sequenced whole genomes of representative human clinical and poultry isolates from the northwestern USA. Genome sequences of these isolates were compared with a global database of S. Kentucky genomes representing 400 ST198 and 50 ST152 strains. The results of the phenotypic, genotypic, and case report data on food consumption and travel show that human infections caused by fluoroquinolone-resistant (FluR) S. Kentucky ST198 in WA State originated from outside of North America. In contrast, fluoroquinolone-susceptible (FluS) S. Kentucky ST198 and S. Kentucky ST152 infection have a likely domestic origin, with domestic cattle and poultry being the potential sources. We also identified lineage-specific non-synonymous single nucleotide polymorphisms (SNPs) that distinguish ST198 and ST152. These SNPs may provide good targets for further investigations on lineage-specific traits such as variation in virulence, metabolic adaptation to different environments, and potential for the development of intervention strategies to improve the safety of food.

Characterization of antibiotic resistance in Escherichia coli isolates from Black-headed gulls (Larus ridibundus) present in the city of Novi Sad, Serbia

Despite common resistance to antimicrobials in Escherichia coli isolates from farm animals in Serbia, no data are currently accessible on its occurrence in E. coli isolated from gulls. Therefore, 67 cloacal swabs and 70 fecal samples from black-headed gulls were investigated for the presence of antibiotic-resistant E. coli isolates. Ninety-nine isolates were obtained during the study. Resistotyping and resistance gene typing has shown that 44 isolates harbor resistance to one or more antibiotics. Multidrug resistance was detected in 24 E. coli isolates. Ten isolates were resistant to extended-spectrum cephalosporin antibiotics and were studied in detail including virulence gene typing, phylogenetic and multilocus sequence typing, and mating. These ten isolates belonged to phylogenetic groups B2 (five isolates), D (four isolates) and B1 (one isolate). Five different sequence types (ST38, ST2307, ST224, ST162 and ST34) were detected in E. coli isolates with AmpC phenotype and genotype. One isolate carried the Inc I2/FIB replicon type plasmid with the bla_CTX-M-1 gene. Nine isolates had bla_CMY-2 genes, which were detected on conjugative plasmids in seven isolates. The virulence genes hly, iroN, iss, ompT and cvaC were detected in one transconjugant. Ten isolates were found to be resistant to ciprofloxacin, whose MIC ranged from 4 to 32 mg/L. Genotyping revealed single or double mutations in the quinolone resistance determining region (QRDR) of the gyrA or gyrA, parC and parE genes, respectively. So, Black-headed gulls from Serbia may be colonized by multidrug-resistant E. coli, some of which are resistant to critically important antibiotics in medicine.

Genomic epidemiology of emerging ESBL-producing Salmonella Kentucky bla CTX-M-14b in Europe

Global dissemination of ciprofloxacin-resistant Salmonella Kentucky has been observed over the past decades. In recent years, there have been reports of extended-spectrum β-lactamase (ESBL) producing S. Kentucky. Routine surveillance at the European Centre for Disease Prevention and Control (ECDC) detected cases with a ciprofloxacin-resistant S. Kentucky with the ESBL-gene bla_CTX-M-14b. Ensuing research identified 78 cases in 2013–2018 in eight European countries. Compared to other S. Kentucky and non-typhoidal Salmonella infections, reported to the European Surveillance System, these cases were more likely to be elderly and to present urinary-tract infections. Bayesian time-scaled phylogeny on whole genome sequences of isolates from these cases and supplementary isolates from public sequence databases was used to infer the origin and spread of this clone. We dated the origin of the bla_CTX-M-14b clone to approximately 2005 in Northern Africa, most likely in Egypt. The geographic origin predicted by the phylogenetic analysis is consistent with the patients’ travel history. Next to multiple introductions of the clone to Europe from Egypt, our analysis suggests that in some parts of Europe the clone might have formed a stable population, from which further spread has occurred. Comparative genomics indicated that the bla_CTX-M-14b gene is present on the bacterial chromosome, within the type VI secretion system region. The bla_CTX-M-14b gene is integrated downstream of the hcp1 gene, on a 2854 bp plasmid fragment containing also ISEcp1. This is the first report of a chromosomally integrated CTX-M gene in Salmonella spp. in Europe, previous studies having identified similar genes only on plasmids.

Epidemic HI2 Plasmids Mobilising the Carbapenemase Gene blaIMP-4 in Australian Clinical Samples Identified in Multiple Sublineages of Escherichia coli ST216 Colonising Silver Gulls

Escherichia coli ST216, including those that carry bla_KPC-2, bla_FOX-5, bla_CTX-M-15 and mcr-1, have been linked to wild and urban-adapted birds and the colonisation of hospital environments causing recalcitrant, carbapenem-resistant human infections. Here we sequenced 22 multiple-drug resistant ST216 isolates from Australian silver gull chicks sampled from Five Islands, of which 21 carried nine or more antibiotic resistance genes including bla_IMP-4 (n = 21), bla_TEM-1b (n = 21), aac(3)-IId (n = 20), mph(A) (n = 20), catB3 (n = 20), sul1 (n = 20), aph(3”)-Ib (n = 18) and aph(6)-Id (n = 18) on FIB(K) (n = 20), HI2-ST1 (n = 11) and HI2-ST3 (n = 10) plasmids. We show that (i) all HI2 plasmids harbour bla_IMP-4 in resistance regions containing In809 flanked by IS26 (HI2-ST1) or IS15DI (HI2-ST3) and diverse metal resistance genes; (ii) HI2-ST1 plasmids are highly related to plasmids reported in diverse Enterobacteriaceae sourced from humans, companion animals and wildlife; (iii) HI2 were a feature of the Australian gull isolates and were not observed in international ST216 isolates. Phylogenetic analyses identified close relationships between ST216 from Australian gull and clinical isolates from overseas. E. coli ST216 from Australian gulls harbour HI2 plasmids encoding resistance to clinically important antibiotics and metals. Our studies underscore the importance of adopting a one health approach to AMR and pathogen surveillance.

Characterizing avian pathogenic Escherichia coli (APEC) from colibacillosis cases, 2018

Colibacillosis caused by avian pathogenic Escherichia coli (APEC) is a devastating disease of poultry that results in multi-million-dollar losses annually to the poultry industry. Disease syndromes associated with APEC includes colisepticemia, cellulitis, air sac disease, peritonitis, salpingitis, omphalitis, and osteomyelitis among others. A total of 61 APEC isolates collected during the Fall of 2018 (Aug-Dec) from submitted diagnostic cases of poultry diagnosed with colibacillosis were assessed for the presence of 44 virulence-associated genes, 24 antimicrobial resistance genes and 17 plasmid replicon types. Each isolate was also screened for its ability to form biofilm using the crystal violet assay and antimicrobial susceptibility to 14 antimicrobials using the NARMS panel. Overall, the prevalence of virulence genes ranged from 1.6% to >90% with almost all strains harboring genes that are associated with the ColV plasmid-the defining trait of the APEC pathotype. Overall, 58 strains were able to form biofilms and only three strains formed negligible biofilms. Forty isolates displayed resistance to antimicrobials of the NARMS panel ranging from one to nine agents. This study highlights that current APEC causing disease in poultry possess virulence and resistance traits and form biofilms which could potentially lead to challenges in colibacillosis control.

Role of Plasmids in the Ecology and Evolution of "High-Risk" Extraintestinal Pathogenic Escherichia coli Clones

Bacterial plasmids have been linked to virulence in Escherichia coli and Salmonella since their initial discovery. Though the plasmid repertoire of these bacterial species is extremely diverse, virulence-associated attributes tend to be limited to a small subset of plasmid types. This is particularly true for extraintestinal pathogenic E. coli, or ExPEC, where a handful of plasmids have been recognized to confer virulence- and fitness-associated traits. The purpose of this review is to highlight the biological and genomic attributes of ExPEC virulence-associated plasmids, with an emphasis on high-risk dominant ExPEC clones. Two specific plasmid types are highlighted to illustrate the independently evolved commonalities of these clones relative to plasmid content. Furthermore, the dissemination of these plasmids within and between bacterial species is examined. These examples demonstrate the evolution of high-risk clones toward common goals, and they show that rare transfer events can shape the ecological landscape of dominant clones within a pathotype.

Evaluation of Live Bacterial Prophylactics to Decrease IncF Plasmid Transfer and Association With Intestinal Small RNAs

Chicken intestinal Escherichia coli are a reservoir for virulence and antimicrobial resistance (AMR) genes that are often carried on incompatibility group F (IncF) plasmids. The rapid transfer of these plasmids between bacteria in the gut contributes to the emergence of new multidrug-resistant and virulent bacteria that threaten animal agriculture and human health. Thus, the aim of the present study was to determine whether live bacterial prophylactics could affect the distribution of large virulence plasmids and AMR in the intestinal tract and the potential role of smRNA in this process. In this study, we tested ∼100 randomly selected E. coli from pullet feces (n = 3 per group) given no treatment (CON), probiotics (PRO), a live Salmonella vaccine (VAX), or both (P + V). E. coli isolates were evaluated via plasmid profiles and several phenotypic (siderophore production and AMR), and genotypic (PCR for virulence genes and plasmid typing) screens. P + V isolates exhibited markedly attenuated siderophore production, lack of AMR and virulence genes, which are all related to the loss of IncF and ColV plasmids (P < 0.0001). To identify a causal mechanism, we evaluated smRNA levels in the ceca mucus and found a positive association between smRNA concentrations and plasmid content, with both being significantly reduced in P + V birds compared to other groups (P < 0.01). To test this positive association between IncF plasmid transfer and host smRNA concentration, we evenly pooled smRNA per group and treated E. coli mating pairs with serial concentrations of smRNA in vitro. Higher smRNA concentrations resulted in greater rates of IncF plasmid transfer between E. coli donors (APEC O2 or VAX isolate IA-EC-001) and recipient (HS-4) (all groups; P < 0.05). Finally, RNAHybrid predictive analyses detected several chicken miRNAs that hybridize with pilus assembly and plasmid transfer genes on the IncF plasmid pAPEC-O2-R. Overall, we demonstrated P + V treatment reduced smRNA levels in the chicken ceca, which was associated with a reduction in potentially virulent E. coli. Furthermore, we propose a novel mechanism in which intestinal smRNAs signal plasmid exchange between E. coli. Investigations to understand the changes in bacterial gene expression as well as smRNAs responsible for this phenomenon are currently underway.

Escherichia coli Sequence Type 457 Is an Emerging Extended-Spectrum-β-Lactam-Resistant Lineage with Reservoirs in Wildlife and Food-Producing Animals

Silver gulls carry phylogenetically diverse Escherichia coli, including globally dominant extraintestinal pathogenic E. coli (ExPEC) sequence types and pandemic ExPEC-ST131 clades; however, our large-scale study (504 samples) on silver gulls nesting off the coast of New South Wales identified E. coli ST457 as the most prevalent. A phylogenetic analysis of whole-genome sequences (WGS) of 138 ST457 samples comprising 42 from gulls, 2 from humans (Australia), and 14 from poultry farmed in Paraguay were compared with 80 WGS deposited in public databases from diverse sources and countries. E. coli ST457 strains are phylogenetic group F, carry fimH145, and partition into five main clades in accordance to predominant flagella H-antigen carriage. Although we identified considerable phylogenetic diversity among the 138 ST457 strains, closely related subclades (<100 SNPs) suggested zoonotic or zooanthroponosis transmission between humans, wild birds, and food-producing animals. Australian human clinical and gull strains in two of the clades were closely related (≤80 SNPs). Regarding plasmid content, country, or country/source, specific connections were observed, including I1/ST23, I1/ST314, and I1/ST315 disseminating bla _CMY-2 in Australia, I1/ST113 carrying bla _CTX-M-8 and mcr-5 in Paraguayan poultry, and F2:A-:B1 plasmids of Dutch origin being detected across multiple ST457 clades. We identified a high prevalence of nearly identical I1/ST23 plasmids carrying bla _CMY-2 among Australian gull and clinical human strains. In summary, ST457 is a broad host range, geographically diverse E. coli lineage that can cause human extraintestinal disease, including urinary tract infection, and displays a remarkable ability to capture mobile elements that carry and transmit genes encoding resistance to critically important antibiotics.

Whole-Genome Sequence Analysis of an Extensively Drug-Resistant Salmonella enterica Serovar Agona Isolate from an Australian Silver Gull (Chroicocephalus novaehollandiae) Reveals the Acquisition of Multidrug Resistance Plasmids

Although most of the approximately 94 million annual human cases of gastroenteritis due to Salmonella enterica resolve without medical intervention, antimicrobial therapy is recommended for patients with severe disease. Wild birds can be natural hosts of Salmonella that pose a threat to human health; however, multiple-drug-resistant serovars of S. enterica have rarely been described. In 2012, silver gull (Chroicocephalus novaehollandiae) chicks at a major breeding colony were shown to host Salmonella, most isolates of which were susceptible to antibiotics. However, multiple-drug-resistant (MDR) Escherichia coli with resistance to carbapenems, ceftazidime, and fluoroquinolones was reported from this breeding colony. In this paper, we describe a novel MDR Salmonella strain subsequently isolated from the same breeding colony. SG17-135, an isolate of S. enterica with phenotypic resistance to 12 individual antibiotics but only nine antibiotic classes including penicillins, cephalosporins, monobactams, macrolides, fluoroquinolones, aminoglycosides, dihydrofolate reductase inhibitors (trimethoprim), sulfonamides, and glycylcyclines was recovered from a gull chick in 2017. Whole-genome sequence (WGS) analysis of SG17-135 identified it as Salmonella enterica serovar Agona (S Agona) with a chromosome comprising 4,813,284 bp, an IncHI2 ST2 plasmid (pSG17-135-HI2) of 311,615 bp, and an IncX1 plasmid (pSG17-135-X) of 27,511 bp. pSG17-135-HI2 housed a complex resistance region comprising 16 antimicrobial resistance genes including bla _CTX-M-55 The acquisition of MDR plasmids by S. enterica described here poses a serious threat to human health. Our study highlights the importance of taking a One Health approach to identify environmental reservoirs of drug-resistant pathogens and MDR plasmids.IMPORTANCE Defining environmental reservoirs hosting mobile genetic elements that shuttle critically important antibiotic resistance genes is key to understanding antimicrobial resistance (AMR) from a One Health perspective. Gulls frequent public amenities, parklands, and sewage and other waste disposal sites and carry drug-resistant Escherichia coli Here, we report on SG17-135, a strain of Salmonella enterica serovar Agona isolated from the cloaca of a silver gull chick nesting on an island in geographic proximity to the greater metropolitan area of Sydney, Australia. SG17-135 is closely related to pathogenic strains of S Agona, displays resistance to nine antimicrobial classes, and carries important virulence gene cargo. Most of the antibiotic resistance genes hosted by SG17-135 are clustered on a large IncHI2 plasmid and are flanked by copies of IS26 Wild birds represent an important link in the evolution and transmission of resistance plasmids, and an understanding of their behavior is needed to expose the interplay between clinical and environmental microbial communities.

Genotypic and Phenotypic Characterization of Incompatibility Group FIB Positive Salmonella enterica Serovar Typhimurium Isolates from Food Animal Sources

Salmonella enterica is one of the most common bacterial foodborne pathogens in the United States, causing illnesses that range from self-limiting gastroenteritis to more severe, life threatening invasive disease. Many Salmonella strains contain plasmids that carry virulence, antimicrobial resistance, and/or transfer genes which allow them to adapt to diverse environments, and these can include incompatibility group (Inc) FIB plasmids. This study was undertaken to evaluate the genomic and phenotypic characteristics of IncFIB-positive Salmonella enterica serovar Typhimurium isolates from food animal sources, to identify their plasmid content, assess antimicrobial resistance and virulence properties, and compare their genotypic isolates with more recently isolated S. Typhimurium isolates from food animal sources. Methods: We identified 71 S. Typhimurium isolates that carried IncFIB plasmids. These isolates were subjected to whole genome sequencing and evaluated for bacteriocin production, antimicrobial susceptibility, the ability to transfer resistance plasmids, and a subset was evaluated for their ability to invade and persist in intestinal human epithelial cells. Results: Approximately 30% of isolates (n = 21) displayed bacteriocin inhibition of Escherichia coli strain J53. Bioinformatic analyses using PlasmidFinder software confirmed that all isolates contained IncFIB plasmids along with multiple other plasmid replicon types. Comparative analyses showed that all strains carried multiple antimicrobial resistance genes and virulence factors including iron acquisition genes, such as iucABCD (75%), iutA (94%), sitABCD (76%) and sitAB (100%). In 17 cases (71%), IncFIB plasmids, along with other plasmid replicon types, were able to conjugally transfer antimicrobial resistance and virulence genes to the susceptible recipient strain. For ten strains, persistence cell counts (27%) were noted to be significantly higher than invasion bacterial cell counts. When the genome sequences of the study isolates collected from 1998–2003 were compared to those published from subsequent years (2005–2018), overlapping genotypes were found, indicating the perseverance of IncFIB positive strains in food animal populations. This study confirms that IncFIB plasmids can play a potential role in disseminating antimicrobial resistance and virulence genes amongst bacteria from several food animal species.

Live Bacterial Prophylactics in Modern Poultry

Commercial poultry farms frequently use live bacterial prophylactics like vaccines and probiotics to prevent bacterial infections. Due to the emergence of antibiotic-resistant bacteria in poultry animals, a closer examination into the health benefits and limitations of commercial, live prophylactics as an alternative to antibiotics is urgently needed. In this review, we summarize the peer-reviewed literature of several commercial live bacterial vaccines and probiotics. Per our estimation, there is a paucity of peer-reviewed published research regarding these products, making repeatability, product-comparison, and understanding biological mechanisms difficult. Furthermore, we briefly-outline significant issues such as probiotic-label accuracy, lack of commercially available live bacterial vaccines for major poultry-related bacteria such as Campylobacter and Clostridium perfringens, as well research gaps (i.e., probiotic-mediated vaccine adjuvancy, gut-brain-microbiota axis). Increased emphasis on these areas would open several avenues for research, ranging from improving protection against bacterial pathogens to using these prophylactics to modulate animal behavior.

Transferable Plasmids of Salmonella enterica Associated With Antibiotic Resistance Genes

Salmonella enterica is a common foodborne illness in the United States and globally. An increasing number of Salmonella infections are resistant to antibiotics, and many of the genes responsible for those resistances are carried by plasmids. Plasmids are important mediators of horizontal gene exchange, which could potentially increase the spread of antibiotic resistance (AR) genes. Twenty-eight different incompatibility groups of plasmids have been described in Enterobacteriaceae. Incompatibility groups differ in their accessory gene content, replication mechanisms, and their associations with Salmonella serotypes and animal sources. Plasmids also differ in their ability to conjugate or be mobilized, essential genes, and conditions required for transfer. It is important to understand the differences in gene content and transfer mechanisms to accurately determine the impact of plasmids on the dissemination and persistence of antibiotic resistance genes. This review will cover the most common plasmid incompatibility groups present in S. enterica with a focus on the transfer mechanisms and associated antibiotic resistance genes.

Iron-Uptake Systems of Chicken-Associated Salmonella Serovars and Their Role in Colonizing the Avian Host

Iron is an essential micronutrient for most bacteria. Salmonella enterica strains, representing human and animal pathogens, have adopted several mechanisms to sequester iron from the environment depending on availability and source. Chickens act as a major reservoir for Salmonella enterica strains which can lead to outbreaks of human salmonellosis. In this review article we summarize the current understanding of the contribution of iron-uptake systems to the virulence of non-typhoidal S. enterica strains in colonizing chickens. We aim to address the gap in knowledge in this field, to help understand and define the interactions between S. enterica and these important hosts, in comparison to mammalian models.

Salmonella enterica's "Choice": Itaconic Acid Degradation or Bacteriocin Immunity Genes

Itaconic acid is an immunoregulatory metabolite produced by macrophages in response to pathogen invasion. It also exhibits antibacterial activity because it is an uncompetitive inhibitor of isocitrate lyase, whose activity is required for the glyoxylate shunt to be operational. Some bacteria, such as Yersinia pestis, encode enzymes that can degrade itaconic acid and therefore eliminate this metabolic inhibitor. Studies, primarily with Salmonella enterica subspecies enterica serovar Typhimurium, have demonstrated the presence of similar genes in this pathogen and the importance of these genes for the persistence of the pathogen in murine hosts. This minireview demonstrates that, based on Blast searches of 1063 complete Salmonella genome sequences, not all Salmonella serovars possess these genes. It is also shown that the growth of Salmonella isolates that do not possess these genes is sensitive to the acid under glucose-limiting conditions. Interestingly, most of the serovars without the three genes, including serovar Typhi, harbor DNA at the corresponding genomic location that encodes two open reading frames that are similar to bacteriocin immunity genes. It is hypothesized that these genes could be important for Salmonella that finds itself in strong competition with other Enterobacteriacea in the intestinal tract—for example, during inflammation.

A Review of Salmonella and Campylobacter in Broiler Meat: Emerging Challenges and Food Safety Measures

Poultry is one of the largest sources of animal-based protein in the United States. Poultry processing has grown from a small local network of plants to nearly 500 plants nationwide. Two of the most persistent bacteria in poultry processing are Salmonella and Campylobacter. It was not until the introduction of Hazard Analysis and Critical Control Point systems in 1996 that major efforts to reduce bacterial contamination were developed. Traditionally, chlorine has been the industry standard for decontaminating chicken meat. However, antimicrobials such as peracetic acid, cetylpyridinium chloride, and acidified sodium chlorite have replaced chlorine as primary antimicrobials. Despite current interventions, the emergence of stress-tolerant and biofilm-forming Salmonella and Campylobacter is of primary concern. In an effort to offset growing tolerance from microbes, novel techniques such as cold plasma treatment, electrostatic spraying, and bacteriophage-based applications have been investigated as alternatives to conventional treatments, while new chemical antimicrobials such as Amplon and sodium ferrate are investigated as well. This review provides an overview of poultry processing in the United States, major microbes in poultry processing, current interventions, emerging issues, and emerging technologies in antimicrobial treatments.

Protection against avian pathogenic Escherichia coli and Salmonella Kentucky exhibited in chickens given both probiotics and live Salmonella vaccine

Commercial poultry farms are increasingly threatened by bacterial infections from avian pathogenic Escherichia coli (APEC) and broad-host Salmonella serovars. Recombinant attenuated Salmonella vaccines (RASV) elicit cross-reactive immune responses against APEC in chickens; however, assessment of broad protection is lacking. Probiotics boost chicken immunity and improve vaccination responses. The objective of this study was to determine whether the RASV, the probiotics, or their combination had protection against APEC and Salmonella. White Leghorn chicks were randomly placed into 4 groups: no treatment (CON), probiotics (PRO), RASV (VAX), or both prophylactics (P + V). Chicks in the PRO and P + V groups were fed probiotics daily, beginning at the age of 1-day-old. Chicks in the P + V and VAX groups were orally inoculated with RASV at the age of 4 D and boosted 2 wks later. Total and antigen-specific IgY responses to Salmonella (lipolysaccharide [LPS]) and E. coli (IroN and IutA) were measured in serum samples via ELISA. Bactericidal potential of both serum and blood against 42 APEC isolates comprising 25 serotypes was assessed in vitro. In vivo protection against APEC was evaluated by air sac challenge with APEC χ7122 (O78:K80), gross pathological lesions were scored, and bacterial loads were enumerated. In a second similar study, birds were orally challenged with S. Kentucky (CVM29188), and feces were enumerated for Salmonella at multiple time points. Vaccination elicited significant LPS-specific antibodies regardless of probiotics (P < 0.0001). Chicks in the P + V group demonstrated increased blood and serum bactericidal abilities against multiple APEC strains in vitro compared with the CON group. Following χ7122 challenge, P+V birds had less APEC in their blood (P < 0.001) and lower signs of airsacculitis (P < 0.01) and pericarditis/perihepatitis (P < 0.05) than CON birds. Finally, only P + V birds were negative for fecal Salmonella at all time points. This study shows this combination treatment may be a feasible method to reduce infection by APEC and Salmonella in chickens.

Non-molecular characterization of pellicle formation by poultry Salmonella Kentucky strains and other poultry-associated Salmonella serovars in Luria Bertani broth

There is limited research concerning the biofilm-forming capabilities of Salmonella Kentucky, a common poultry isolate. The objective was to quantitate pellicle formation of S. Kentucky versus better-characterized Salmonella strains of Enteritidis and Heidelberg. In separate experiments, Salmonella strains and serovars were tested for their biofilm-forming abilities in different Luria-Bertani (LB) broths (1); pellicle formation in different volumes of LB without salt (2); and the potential priming effects on formation after pellicles were transferred three consecutive times (3). Data were analyzed using One-Way ANOVA with means separated using Tukey's HSD (P ≤ 0.05). In the first experiment, there was no significant effect between strain and serovars (P > 0.05), but media type affected pellicle formation significantly with LB Miller and LB minus NaCl plus 2% glucose resulting in no pellicle formation (P < 0.001). When grown in 50 mL, Kentucky 38-0085 produced larger pellicles than Kentucky 38-0055, and Heidelberg strain 38-0127 (P < 0.0001). Serial transfers of pellicles did not significantly affect pellicle formation (P > 0.05); however, Kentucky 38-0084, 38-0085 and 38-0086 produced larger pellicles than Kentucky 38-0055 and 38-0056 and Heidelberg 38-0126, 38-0127 and 38-0152. The current study demonstrates the consistent biofilm forming capabilities of Kentucky and may explain why Kentucky is frequently isolated in poultry processing facilities.

Evaluation of Incompatibility Group I1 (IncI1) Plasmid-Containing Salmonella enterica and Assessment of the Plasmids in Bacteriocin Production and Biofilm Development

Mobile genetic elements, such as plasmids, can potentially increase the ability of bacteria to infect and persist in vertebrate host cells. IncI1 plasmids are widely distributed in Salmonella from food animal sources and associated with clinically important strains. These plasmids often encode antimicrobial resistance; however, little is known about their impact on the virulence of Salmonella strains. To assess the potential impact of the plasmids on virulence, 43 IncI1-positive Salmonella isolates from human and animal sources were subjected to whole genome sequence (WGS) analyses and evaluated for their abilities to invade and persist for 48 h in Caco-2 human intestinal epithelial cells, form biofilms and encode bacteriocins. Draft WGS data were submitted to predict the presence of virulence and antimicrobial resistance genes, plasmid replicon types present, conduct plasmid multilocus sequence typing (pMLST), and core genome MLST (cgMLST) in the isolates. Caco-2 cells were infected with Salmonella strains and incubated for both one and 48 h for the invasion and persistence assays, respectively. Additionally, Salmonella isolates and IncI1 plasmid carrying transconjugants (n = 12) generated in Escherichia coli were assessed for their ability to produce biofilms and bacteriocin inhibition of growth of other bacteria. All Salmonella isolates infected Caco-2 cells and persisted in the cells at 48 hrs. Persistent cell counts were observed to be significantly higher than invasion assay cell counts in 26% of the isolates. Among the IncI1 plasmids, there were 18 pMLST types. Nearly 35% (n = 15) of Salmonella isolates produced biofilms; however, none of the IncI1-positive transconjugants produced increased biofilms compared to the recipient. Approximately 65% (n = 28) of isolates and 67% (n = 8) of IncI1-positive transconjugants were able to inhibit growth of at least one E. coli strain; however, none inhibited the growth of strains from species other than E. coli. The study characterized IncI1 positive Salmonella isolates and provided evidence about the potential contributions of IncI1 plasmids virulence phenotypes and areas where they do not. These findings should allow for more focused efforts to assess the impact of plasmids on bacterial pathophysiology and human health.

Genome analysis of antimicrobial resistance, virulence, and plasmid presence in Turkish Salmonella serovar Infantis isolates

Salmonella enterica subsp. enterica serovar Infantis (S. Infantis) isolates were found to have a multi-drug resistance profile (kanamycin, streptomycin, nalidixic acid, tetracycline, sulfonamide, and sometimes to ampicillin) and high prevalence (91%) in Turkish poultry in our previous studies. To investigate the mechanism behind multi-drug antimicrobial resistance (AMR) and high prevalence in Turkish poultry, 23 of the isolates were sequenced for comparative genomic analyses including: SNP-based comparison to S. Infantis from other countries, comparison of antimicrobial resistance genes (AMGs) with AMR phenotypes, and plasmid identification and annotation. Whole-genome SNP-based phylogenetic analysis found that all 23 Turkish S. Infantis isolates formed a distinct, well-supported clade, separate from 243 comparison S. Infantis genomes in GenomeTrakr identified as from the US and EU; the isolates most closely related to the cluster of these Turkish isolates were from Israel and Egypt. AMGs identified by bioinformatic analysis, without differentiating chromosomal or plasmid located genes, implied AMR phenotypes with 94% similarity overall to wet lab data, which was performed by phenotypic and conventional PCR methods. Most of the S. Infantis (21/23) isolates had identifiable plasmids, with 76% (16/21) larger than 100 kb and 48% (10/21) larger than 200 kb. A plasmid larger than 200 kb, with the incompatibility type of IncX1, similar to United States S. Infantis plasmid N55391 (99% query coverage and 99% identity overall), which itself is similar to Italian and Hungarian S. Infantis plasmids. Turkish S. Infantis plasmids had different beta-lactam resistance genes (bla_TEM-70, bla_TEM-148 and bla_TEM-₁₉₈) than the gene bla_CTX-M-65 found in S. Infantis plasmids from other countries. This is the first observation of these three genes in S. Infantis isolates. The plasmids larger than 200 kb had two distinct regions of interest: Site 1 and Site 2. Site 1 (around 130 kb) had virulence- and bacteriocin- associated genes such as bacteriocin secretion system and type II toxin-antitoxin system genes (vagC, ccdA, ccdB, mchE, cvaB) and an aminoglycoside resistance gene (str). Site 2 (around 75-110 kb) had the antimicrobial resistance genes (aadA, sulI, tetA, tetR) and mercury (mer) resistance gene on tranposons Tn552 and Tn501. Presence of these AMR and virulence genes suggests they may have a role in the emergence of S. Infantis in poultry and support treating this serotype as a an important human health hazard.

Worldwide Epidemiology of Salmonella Serovars in Animal-Based Foods: a Meta-analysis

Salmonella spp. are among the most important foodborne pathogens and the third leading cause of human death among diarrheal diseases worldwide. Animals are the primary source of this pathogen, and animal-based foods are the main transmission route to humans. Thus, understanding the global epidemiology of Salmonella serovars is key to controlling and monitoring this bacterium. In this context, this study aimed to evaluate the prevalence and diversity of Salmonella enterica serovars in animal-based foods (beef, pork, poultry, and seafood) throughout the five continents (Africa, the Americas [North and Latin America], Asia, Europe, and Oceania). The meta-analysis consisted of a chemometric assessment (hierarchical cluster analysis and principal component analysis) to identify the main epidemiological findings, including the prevalence and diversity of the Salmonella serovars in each matrix. Regarding the serovar distribution, S Typhimurium presented a cosmopolitan distribution, reported in all four assessed matrices and continents; poultry continues to play a central role in the dissemination of the Enteritidis serovar to humans, and Anatum and Weltevreden were the most frequently found in beef and seafood, respectively. Additionally, we recommended careful monitoring of certain serovars, such as Derby, Agona, Infantis, and Kentucky. Finally, given the scientific data regarding the most frequently reported serovars and which matrices constitute the main vehicles for the transmission of this pathogen, control programs may be improved, and specific interventions may be implemented in an attempt to reduce the risk of this pathogen reaching humans.IMPORTANCE Salmonellosis is caused by Salmonella spp. and is the third leading cause of death among food-transmitted diseases. This pathogen is commonly disseminated in domestic and wild animals, and the infection's symptoms are characterized by acute fever, nausea, abdominal pain, and diarrhea. The animals are the primary source of salmonellae, and animal-based foods are the main transmission route to humans. Therefore, data collected from these sources could contribute to future global interventions for effective control and surveillance of Salmonella along the food chain. In light of this, the importance of our research is in identifying the prevalence of Salmonella serovars in four animal-based food matrices (pork, poultry, beef, and seafood) and to evaluate the importance that each matrix has as the primary source of this pathogen to humans.

Global transcriptomic analyses of Salmonella enterica in Iron-depleted and Iron-rich growth conditions

Background

Salmonella enterica possess several iron acquisition systems, encoded on the chromosome and plasmids. Recently, we demonstrated that incompatibility group (Inc) FIB plasmid-encoded iron acquisition systems (Sit and aerobactin) likely play an important role in persistence of Salmonella in human intestinal epithelial cells (Caco-2). In this study, we sought to determine global transcriptome analyses of S. enterica in iron-rich (IR) and iron-depleted (ID) growth conditions.

Results

The number of differentially-expressed genes were substantially higher for recipient (SE819) (n = 966) and transconjugant (TC) (n = 945) compared to the wild type (WT) (SE163A) (n = 110) strain in ID as compared to IR growth conditions. Several virulence-associated factors including T3SS, flagellin, cold-shock protein (cspE), and regulatory genes were upregulated in TC in ID compared to IR conditions. Whereas, IS1 and acrR/tetR transposases located on the IncFIB plasmid, ferritin and several regulatory genes were downregulated in TC in ID conditions. Enterobactin transporter (entS), iron ABC transporter (fepCD), colicin transporter, IncFIB-encoded enolase, cyclic di-GMP regulator (cdgR) and other regulatory genes of the WT strain were upregulated in ID compared to IR conditions. Conversely, ferritin, ferrous iron transport protein A (feoA), IncFIB-encoded IS1 and acrR/tetR transposases and ArtA toxin of WT were downregulated in ID conditions. SDS-PAGE coupled with LC-MS/MS analyses revealed that siderophore receptor proteins such as chromosomally-encoded IroN and, IncFIB-encoded IutA were upregulated in WT and TC in ID growth conditions. Both chromosome and IncFIB plasmid-encoded SitA was overexpressed in WT, but not in TC or recipient in ID conditions. Increased expression of flagellin was detected in recipient and TC, but not in WT in ID conditions.

Conclusion

Iron concentrations in growth media influenced differential gene expressions both at transcriptional and translational levels, including genes encoded on the IncFIB plasmid. Limited iron availability within the host may promote pathogenic Salmonella to differentially express subsets of genes encoded by chromosome and/or plasmids, facilitating establishment of successful infection.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5768-0) contains supplementary material, which is available to authorized users.

Antimicrobial Resistance Genes, Cassettes, and Plasmids Present in Salmonella enterica Associated With United States Food Animals

The ability of antimicrobial resistance (AR) to transfer, on mobile genetic elements (MGEs) between bacteria, can cause the rapid establishment of multidrug resistance (MDR) in bacteria from animals, thus creating a foodborne risk to human health. To investigate MDR and its association with plasmids in Salmonella enterica, whole genome sequence (WGS) analysis was performed on 193 S. enterica isolated from sources associated with United States food animals between 1998 and 2011; 119 were resistant to at least one antibiotic tested. Isolates represented 86 serotypes and variants, as well as diverse phenotypic resistance profiles. A total of 923 AR genes and 212 plasmids were identified among the 193 strains. Every isolate contained at least one AR gene. At least one plasmid was detected in 157 isolates. Genes were identified for resistance to aminoglycosides (n = 472), β-lactams (n = 84), tetracyclines (n = 171), sulfonamides (n = 91), phenicols (n = 42), trimethoprim (n = 8), macrolides (n = 5), fosfomycin (n = 48), and rifampicin (n = 2). Plasmid replicon types detected in the isolates were A/C (n = 32), ColE (n = 76), F (n = 43), HI1 (n = 4), HI2 (n = 20), I1 (n = 62), N (n = 4), Q (n = 7), and X (n = 35). Phenotypic resistance correlated with the AR genes identified in 95.4% of cases. Most AR genes were located on plasmids, with many plasmids harboring multiple AR genes. Six antibiotic resistance cassette structures (ARCs) and one pseudo-cassette were identified. ARCs contained between one and five resistance genes (ARC1: sul2, strAB, tetAR; ARC2: aac3-iid; ARC3: aph, sph; ARC4: cmy-2; ARC5: floR; ARC6: tetB; pseudo-ARC: aadA, aac3-VIa, sul1). These ARCs were present in multiple isolates and on plasmids of multiple replicon types. To determine the current distribution and frequency of these ARCs, the public NCBI database was analyzed, including WGS data on isolates collected by the USDA Food Safety and Inspection Service (FSIS) from 2014 to 2018. ARC1, ARC4, and ARC5 were significantly associated with cattle isolates, while ARC6 was significantly associated with chicken isolates. This study revealed that a diverse group of plasmids, carrying AR genes, are responsible for the phenotypic resistance seen in Salmonella isolated from United States food animals. It was also determined that many plasmids carry similar ARCs.

A review of Salmonella enterica with particular focus on the pathogenicity and virulence factors, host specificity and antimicrobial resistance including multidrug resistance

Salmonella genus represents the most common foodborne pathogens frequently isolated from food-producing animals that is responsible for zoonotic infections in humans and animal species including birds. Thus, Salmonella infections represent a major concern to public health, animals, and food industry worldwide. Salmonella enterica represents the most pathogenic specie and includes > 2600 serovars characterized thus far. Salmonella can be transmitted to humans along the farm-to-fork continuum, commonly through contaminated foods of animal origin, namely poultry and poultry-related products (eggs), pork, fish etc. Some Salmonella serovars are restricted to one specific host commonly referred to as "host-restricted" whereas others have broad host spectrum known as "host-adapted" serovars. For Salmonella to colonize its hosts through invading, attaching, and bypassing the host's intestinal defense mechanisms such as the gastric acid, many virulence markers and determinants have been demonstrated to play crucial role in its pathogenesis; and these factors included flagella, capsule, plasmids, adhesion systems, and type 3 secretion systems encoded on the Salmonella pathogenicity island (SPI)-1 and SPI-2, and other SPIs. The epidemiologically important non-typhoidal Salmonella (NTS) serovars linked with a high burden of foodborne Salmonella outbreaks in humans worldwide included Typhimurium, Enteritidis, Heidelberg, and Newport. The increased number of NTS cases reported through surveillance in recent years from the United States, Europe and low- and middle-income countries of the world suggested that the control programs targeted at reducing the contamination of food animals along the food chain have largely not been successful. Furthermore, the emergence of several clones of Salmonella resistant to multiple antimicrobials worldwide underscores a significant food safety hazard. In this review, we discussed on the historical background, nomenclature and taxonomy, morphological features, physical and biochemical characteristics of NTS with a particular focus on the pathogenicity and virulence factors, host specificity, transmission, and antimicrobial resistance including multidrug resistance and its surveillance.

A real-time PCR regimen for testing environmental samples for Salmonella enterica subsp. enterica serovars of concern to the poultry industry, with special focus on Salmonella Enteritidis

A real-time PCR (qPCR) regimen, using up to six genetic targets, was developed to rapidly detect Salmonella and in particular identify Salmonella Enteritidis. The test regimen was first evaluated using a reference culture collection of Salmonella to confirm the appropriateness of the selected targets, which included up to three genetic markers for discrimination of Salmonella Enteritidis from other Salmonella serovars commonly found in poultry facilities. The qPCR procedure was then compared with culture methods used to detect Salmonella using a collection of enrichment broths previously generated from 239 environmental samples collected from a large number of hatchery facilities across Canada over several years. The qPCR regimen facilitated specific detection of Salmonella Enteritidis, and on a sample basis, it showed excellent agreement with the culture methods. Moreover, in many cases, qPCR detected Salmonella earlier in the culture process than did the culture method. Application of this method will significantly shorten test times and allow more timely identification of infected poultry premises, thereby improving present programmes aimed at controlling Salmonella Enteritidis at the environmental source.

Draft Genome Sequences of Salmonella enterica Serovar Enteritidis and Kentucky Isolates from Retail Poultry Sources

The draft genome sequences of four Salmonella enterica serovar Enteritidis and Kentucky isolates were evaluated for biofilm formation and antibiotic resistance. The Salmonella serovar Kentucky strains CFS84 and CFS85 and Salmonella serovar Enteritidis strains CFS86 and CFS87 were isolated from retail poultry sources in Arkansas.