Foodborne Pathogens and Disease

Vibrio parahaemolyticus is the leading cause of seafood-related foodborne illness globally. In 2018, the U.S. federal, state, and local public health and regulatory partners investigated a multistate outbreak of V. parahaemolyticus infections linked to crabmeat that resulted in 26 ill people and nine hospitalizations. State and U.S. Food and Drug Administration (FDA) laboratories recovered V. parahaemolyticus, Salmonella spp., and Listeria monocytogenes isolates from crabmeat samples collected from various points of distribution and conducted phylogenetic analyses of whole-genome sequencing data. Federal, state, and local partners conducted traceback investigations to determine the source of crabmeat. Multiple Venezuelan processors that supplied various brands of crabmeat were identified, but a sole firm was not confirmed as the source of the outbreak. Travel restrictions between the United States and Venezuela prevented FDA officials from conducting on-site inspections of cooked crabmeat processors. Based on investigation findings, partners developed public communications advising consumers not to eat crabmeat imported from Venezuela and placed potentially implicated firms on import alerts. While some challenges limited the scope of the investigation, epidemiologic, traceback, and laboratory evidence identified the contaminated food and country of origin, and contributed to public health and regulatory actions, preventing additional illnesses. This multistate outbreak illustrates the importance of adhering to appropriate food safety practices and regulations for imported seafood.

Salmonella enterica serovar Agona is commonly detected in raw animal feed components during routine microbial monitoring of Australian commercial animal feed mills. We hypothesized that Salmonella-contaminated raw feed components originate at the rendering or oil seed crushing plant and are distributed to mills in different locations. Our objective was to investigate the source of Salmonella Agona contaminated raw feed components. Whole genome sequences of 37 Salmonella Agona isolates, 36 from raw feed components and 1 from finished feed, collected from 10 Australian feed mills located in 4 Australian states, were compared using core genome phylogenetic analysis. After DNA extraction and de novo draft assembly of the paired reads, the draft genomes were aligned using conserved signature indel phylogeny against a reference genome for Salmonella Agona, to identify single nucleotide polymorphisms in the core genome. Five distinct clades corresponding to the five different suppliers of Salmonella Agona-contaminated raw feed components were identified in the resulting phylogenetic tree. The results also provided evidence of cross-transference of Salmonella Agona between canola meal, meat meal, and finished feed within a mill. Core genome phylogenetic analysis facilitated tracing the source of Salmonella contamination in feed mills.

Shigella sonnei, the causative agents of bacillary dysentery, remains a significant threat to public health. Litsea cubeba essential oil (LC-EO), one of the natural essential oils, exhibited promising biological activities. In this study, the antibacterial effects and possible mechanisms of LC-EO on S. sonnei and its application in lettuce medium were investigated. The minimum inhibitory concentration (MIC) of LC-EO against S. sonnei ATCC 25931 and CMCC 51592 was 4 and 6 μL/mL, respectively. The LC-EO could inhibit the growth of S. sonnei, and decreased S. sonnei to undetectable levels with 4 μL/mL for 1 h in Luria-Bertani broth. The antibacterial mechanism indicated that after the treatment of LC-EO, the production of reactive oxygen species and the activity of superoxide dismutase were significantly elevated in S. sonnei cells, and eventually led to the lipid oxidation product, the malondialdehyde content that significantly increased. Moreover, LC-EO at 2 MIC could destroy 96.51% of bacterial cell membrane integrity, and made S. sonnei cells to appear wrinkled with a rough surface, so that the intracellular adenosine triphosphate leakage was about 0.352–0.030 μmol/L. Finally, the results of application evaluation indicated that the addition of LC-EO at 4 μL/mL in lettuce leaves and 6 μL/mL in lettuce juice could decrease the number of S. sonnei to undetectable levels without remarkable influence on the lettuce leaf sensory quality. In summary, LC-EO exerted strong antibacterial activity and has the potential to control S. sonnei in food industry.

Vibrio parahaemolyticus is a foodborne pathogenic bacterium commonly found in seafood. The emergence of drug-resistant strains poses a threat to human public health and economic development. Therefore, there are increasing needs to develop new technologies in controlling multidrug-resistant V. parahaemolyticus strains and to evaluate their practical efficiency in seafood or mariculture. In this study, we screened two genetically related V. parahaemolyticus phages, F23s2 and H256D1, which belonged to the siphoviridae family and podoviridae family, respectively. They showed 97.13% and 96.13% identity with Vibrio phage vB_Vpap_MGD1, respectively. Both phages were stable at pH 4–11 and displayed temperature tolerance (<70°C). Meanwhile they showed a broad host spectrum for multidrug-resistant V. parahaemolyticus, and Phage F23s2 lysed 16 of all 23 V. parahaemolyticus strains, while phage H256D1 lysed 10 strains. Phage F23s2 and H256D1 had a good inhibitory effect on V. parahaemolyticus in shrimp meat. Compared with the negative group, the bacterial amount of experimental group with phage F23s2 decreased by 1.60 log colony-forming unit (CFU)/mL at 12 h. For phage H256D1, the bacterial concentration of shrimp meat contaminated with V. parahaemolyticus H256 increased to 5.65 log CFU/mL at 72 h, while the concentration of the experimental group in presence of phage H256D1 was 3.58 log CFU/mL. All live clams infected with V. parahaemolyticus died after 96 h in the absence of phage, whereas clams with phage F23s2 and H256D1 still had a survival rate of 12% and 4%, respectively. Understanding the gene function and biology of phages facilitates its application for control of V. parahaemolyticus contamination worldwide.

Invasive listeriosis is a rare but serious foodborne disease that causes maternal–neonatal, central nervous system, and bloodstream infections. The aim of this study was to assess the whole-genome sequencing (WGS)-based genetic diversity of clinical Listeria monocytogenes isolates over a 7-year period and prove the effect of WGS application in food vehicle investigation. A total of 360 isolates were recovered during 2013 and 2019 through the national listeriosis special surveillance program. Two hundred twenty-six isolates (62.8%) were associated with pregnancy. All isolates belonged to lineage I (214 isolates) or lineage II (146 isolates), with 4 serogroups (46.9% IIb, 39.7% IIa, 12.5% IVb, and 0.8% IIc). All isolates were in 25 clonal complexes (CCs) and 3 singletons, with CC87, CC8, and CC5 being the most common causes of human listeriosis. All clinical isolates were positive for Listeria pathogenicity island 1 (LIPI-1), LIPI-3 was present in 21.4% of isolates and LIPI-4 was detected in 29.2% of isolates. LIPI-4-positive isolates, including CC87, sequence type (ST)619, ST382, CC4, and CC2, have been shown to confer hypervirulence. Fifteen isolates harbored at least one antimicrobial encoding gene, including tet (M), mef (A), msr (D), and dfr (G). The sublineage designations were consistent with CC designations, and 215 distinct cgMLST types (CTs) were classified, the most abundant being CT58 and CT750. In summary, there is a high level of genetic diversity among the clinical isolates. WGS has strengthened listeriosis surveillance and will be implemented for other foodborne bacteria in the National Molecular Tracing Network for Foodborne Disease.