Evaluation of the Illumina iSeq whole genome sequencing system for enteric disease surveillance and outbreak detection.

The Illumina iSeq low-capacity sequencing platform was evaluated for use in foodborne disease surveillance and outbreak detection. The platform produced high quality sequence data comparable to that of the Illumina MiSeq and was cost-effective with fast turn-around time in low sample volume environments.

Gen-FS coordinated proficiency test data for genomic foodborne pathogen surveillance, 2017 and 2018 exercises.

The US PulseNet and GenomeTrakr laboratory networks work together within the Genomics for Food Safety (Gen-FS) consortium to collect and analyze genomic data for foodborne pathogen surveillance (species include Salmonella enterica, Listeria monocytogenes, Escherichia coli (STECs), and Campylobactor). In 2017 these two laboratory networks started harmonizing their respective proficiency test exercises, agreeing on distributing a single strain-set and following the same standard operating procedure (SOP) for genomic data collection, running a jointly coordinated annual proficiency test exercise. In this data release we are publishing the reference genomes and raw data submissions for the 2017 and 2018 proficiency test exercises.

Insights into the environmental reservoir of pathogenic Vibrio parahaemolyticus using comparative genomics.

Vibrio parahaemolyticus is an aquatic halophilic bacterium that occupies estuarine and coastal marine environments, and is a leading cause of seafood-borne food poisoning cases. To investigate the environmental reservoir and potential gene flow that occurs among V. parahaemolyticus isolates, the virulence-associated gene content and genome diversity of a collection of 133 V. parahaemolyticus isolates were analyzed. Phylogenetic analysis of housekeeping genes, and pulsed-field gel electrophoresis, demonstrated that there is genetic similarity among V. parahaemolyticus clinical and environmental isolates. Whole-genome sequencing and comparative analysis of six representative V. parahaemolyticus isolates was used to identify genes that are unique to the clinical and environmental isolates examined. Comparative genomics demonstrated an O3:K6 environmental isolate, AF91, which was cultured from sediment collected in Florida in 2006, has significant genomic similarity to the post-1995 O3:K6 isolates. However, AF91 lacks the majority of the virulence-associated genes and genomic islands associated with these highly virulent post-1995 O3:K6 genomes. These findings demonstrate that although they do not contain most of the known virulence-associated regions, some V. parahaemolyticus environmental isolates exhibit significant genetic similarity to clinical isolates. This highlights the dynamic nature of the V. parahaemolyticus genome allowing them to transition between aquatic and host-pathogen states.

Retrospective analysis of Salmonella, Campylobacter, Escherichia coli, and Enterococcus in animal feed ingredients.

The presence and antimicrobial susceptibility of foodborne pathogens and indicator organisms in animal feed are not well understood. In this study, a total of 201 feed ingredient samples (animal byproducts, n=122; plant byproducts, n=79) were collected in 2002 and 2003 from representative rendering plants and the oilseed (or cereal grain) industry across the United States. The occurrence and antimicrobial susceptibility of four bacterial genera (Salmonella, Campylobacter, Escherichia coli, and Enterococcus) were determined. Salmonella isolates were further characterized by serotyping and pulsed-field gel electrophoresis (PFGE). None of the samples yielded Campylobacter or E. coli O157:H7, whereas Salmonella, generic E. coli, and Enterococcus were present in 22.9%, 39.3%, and 86.6% of samples, respectively. A large percentage (47.8%) of Salmonella-positive samples harbored two serovars, and the vast majority (88.4%) of Enterococcus isolates were E. faecium. Animal byproducts had a significantly higher Salmonella contamination rate (34.4%) than plant byproducts (5.1%) (p<0.05). Among 74 Salmonella isolates recovered, 27 serovars and 55 PFGE patterns were identified; all were pan-susceptible to 17 antimicrobials tested. E. coli isolates (n=131) demonstrated similar susceptibility to these antimicrobials except for tetracycline (15.3% resistance), sulfamethoxazole (7.6%), streptomycin (4.6%), ampicillin (3.8%), and nalidixic acid (1.5%). Enterococcus isolates (n=362) were also resistant to five of 17 antimicrobials tested, ranging from 1.1% to penicillin to 14.6% to tetracycline. Resistance rates were generally higher among isolates recovered from animal byproducts. Taken together, our findings suggest that diverse populations of Salmonella, E. coli, and Enterococcus are commonly present in animal feed ingredients, but antimicrobial resistance is not common. Future large-scale studies to monitor these pathogenic and indicator organisms in feed commodities is warranted.

Genome Sequences of Salmonella enterica Serovar Heidelberg Isolates Isolated in the United States from a Multistate Outbreak of Human Salmonella Infections.

Salmonella enterica is recognized as one of the most common bacterial agents of foodborne illness. We report draft genomes of four Salmonella serovar Heidelberg isolates associated with the recent multistate outbreak of human Salmonella Heidelberg infections linked to kosher broiled chicken livers in the United States in 2011. Isolates 2011K-1259 and 2011K-1232 were recovered from humans, whereas 2011K-1724 and 2011K-1726 were isolated from chicken liver. Whole genome sequence analysis of these isolates provides a tool for studying the short-term evolution of these epidemic clones and can be used for characterizing potentially new virulence factors.

Outbreak of human Salmonella Typhimurium infections linked to contact with baby poultry from a single agricultural feed store chain and mail-order hatchery, 2009.

BACKGROUND: Over 30 outbreaks of human salmonellosis linked to contact with live poultry from mail-order hatcheries were reported to Centers for Disease Control and Prevention between 1990 and 2010. In May 2009, we investigated an outbreak of human Salmonella Typhimurium infections, primarily affecting children. METHODS: A case was defined as a person with the outbreak strain of Salmonella Typhimurium, as determined by pulsed-field gel electrophoresis and multiple-locus variable-number tandem repeat analysis, in a Pennsylvania or New York resident with illness onset between May 1 and September 1, 2009. We conducted a case-control study to examine the relationship between illness and live poultry contact. Controls were age-matched and geographically-matched. Traceback and environmental investigations were conducted. RESULTS: We identified 36 case-patients in Pennsylvania and New York; 36% were children aged ≤5 years. Case-patients were more likely than controls to report live baby poultry contact (matched odds ratio [mOR]: 17.0; 95% confidence interval [CI]: 2.7-710.5), contact with chicks (mOR: 14.0; 95% CI: 2.1-592.0), ducklings (mOR: 8.0; 95% CI: 1.1-355.0) and visiting agricultural feed stores (mOR: 6.0; 95% CI: 1.3-55.2). Most (83%) visited agricultural Feed Store Chain Y, a national agricultural feed store chain, which received poultry from Hatchery C, which is supplied by multiple egg sources. Salmonella Typhimurium was isolated from a source duck flock, but had a different pulsed-field gel electrophoresis pattern than the outbreak strain. CONCLUSIONS: Live baby poultry remain an important source of human salmonellosis, particularly among children. Preventing these infections requires comprehensive interventions at hatcheries and agricultural feed stores; pediatricians should inform patients of risks associated with live poultry contact.

Multilaboratory validation study of standardized multiple-locus variable-number tandem repeat analysis protocol for shiga toxin-producing Escherichia coli O157: a novel approach to normalize fragment size data between capillary electrophoresis platforms.

The PulseNet USA subtyping network recently established a standardized protocol for multiple-locus variable-number tandem repeat analysis (MLVA) to characterize Shiga toxin-producing Escherichia coli O157. To enable data comparisons from different laboratories in the same database, reproducibility and high quality of the data must be ensured. The aim of this study was to test the robustness and reproducibility of the proposed standardized protocol by subjecting it to a multilaboratory validation process and to address any discrepancies that may have arisen from the study. A set of 50 strains was tested in 10 PulseNet participating laboratories that used capillary electrophoresis instruments from two manufacturers. Six out of the 10 laboratories were able to generate correct MLVA types for 46 (92%) or more strains. The discrepancies in MLVA type assignment were caused mainly by difficulties in optimizing polymerase chain reactions that were attributed to technical inexperience of the staff and suboptimal quality of reagents and instrumentation. It was concluded that proper training of staff must be an integral part of technology transfer. The interlaboratory reproducibility of fragment sizing was excellent when the same capillary electrophoresis platform was used. However, sizing discrepancies of up to six base pairs for the same fragment were detected between the two platforms. These discrepancies were attributed to different dye and polymer chemistries employed by the manufacturers. A novel software script was developed to assign alleles based on two platform-specific (Beckman Coulter CEQ8000 and Applied Biosystems Genetic Analyzer 3130xl) look-up tables containing fragment size ranges for all alleles. The new allele assignment method was validated at the PulseNet central laboratory using a diverse set of 502 Shiga toxin-producing Escherichia coli O157 isolates. The validation confirmed that the script reliably assigned the same allele for the same fragment regardless of the platform used to size the fragment.

Rapid identification of Vibrio parahaemolyticus by whole-cell matrix-assisted laser desorption ionization-time of flight mass spectrometry.

Vibrio parahaemolyticus is a pathogenic marine bacterium that is the main causative agent of bacterial seafood-borne gastroenteritis in the United States. An increase in the frequency of V. parahaemolyticus-related infections during the last decade has been attributed to the emergence of an O3:K6 pandemic clone in 1995. The diversity of the O3:K6 pandemic clone and its serovariants has been examined using multiple molecular techniques including multilocus sequence analysis, pulsed-field gel electrophoresis, and group-specific PCR analysis. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has become a powerful tool for rapidly distinguishing between related bacterial species. In the current study, we demonstrate the development of a whole-cell MALDI-TOF MS method for the distinction of V. parahaemolyticus from other Vibrio spp. We identified 30 peaks that were present only in the spectra of the V. parahaemolyticus strains examined in this study that may be developed as MALDI-TOF MS biomarkers for identification of V. parahaemolyticus. We detected variation in the MALDI-TOF spectra of V. parahaemolyticus strains isolated from different geographical locations and at different times. The MALDI-TOF MS spectra of the V. parahaemolyticus strains examined were distinct from those of the other Vibrio species examined including the closely related V. alginolyticus, V. harveyi, and V. campbellii. The results of this study demonstrate the first use of whole-cell MALDI-TOF MS analysis for the rapid identification of V. parahaemolyticus.