Research Publications (Food Safety)

Shigella is an important human-adapted pathogen which contributes to a large global burden of diarrhoeal disease. Together with the increasing threat of antimicrobial resistance and lack of an effective vaccine, there is great urgency to identify novel therapeutics and preventatives to combat Shigella infection. In this review, we discuss the development of innovative technologies and animal models to study mechanisms underlying Shigella infection of humans.

Enterococcus faecalis and Staphylococcus aureus are frequently co-isolated from biofilm-associated infections. A new study by Ch’ng et al. revealed that S. aureus-released heme feeds E. faecalis respiration, augmenting E. faecalis growth and overall biofilm biomass. Their finding further supports the theory that metabolite cross-feeding is a critical aspect shaping polymicrobial biofilm interactions.

The fulminating zoonotic pathogen Vibrio vulnificus is the causative agent of fatal septicemia in humans and fish, raising tremendous economic burdens in healthcare and the aquaculture industry. V. vulnificus exploits various virulence factors, including biofilm-related factors and exotoxins, for its persistence in nature and pathogenesis during infection.

The gut microbiome of neonates, infants, and toddlers (NITs) is very dynamic, and only begins to stabilize towards the third year of life. Within this period, exposure to xenobiotics may perturb the gut environment, thereby driving or contributing to microbial dysbiosis, which may negatively impact health into adulthood.

Modern microbial taxonomy generally relies on the use of single marker genes or sets of concatenated genes to generate a framework for the delineation and classification of organisms at different taxonomic levels. However, given that DNA is the 'blueprint of life', and hence the ultimate arbiter of taxonomy, classification systems should attempt to use as much of the blueprint as possible to capture a comprehensive phylogenetic signal.

Intestinal pathogens must combat host and microbiota-associated resistance to establish an infection. A new study (Shelton et al.) highlights how Salmonella manipulates the mammalian host to produce anaerobic respiratory electron acceptors, allowing catabolism of propionate and providing a competitive edge to Salmonella residing in the gut.

Type III secretion system (T3SS) effectors are key virulence factors that underpin the infection strategy of many clinically important Gram-negative pathogens, including Salmonella enterica, Shigella spp., enteropathogenic and enterohemorrhagic Escherichia coli and their murine equivalent, Citrobacter rodentium. The cellular processes or proteins targeted by the effectors can be common to multiple pathogens or pathogen-specific.

Emerging zoonotic diseases exert a significant burden on human health and have considerable socioeconomic impact worldwide. In Asia, live animals as well as animal products are commonly sold in informal markets. The interaction of humans, live domestic animals for sale, food products, and wild and scavenging animals, creates a risk for emerging infectious diseases.

Listeria monocytogenes is a foodborne pathogen responsible for listeriosis, an infection that can manifest in humans as bacteremia, meningoencephalitis in immunocompromised patients and the elderly, and fetal-placental infection in pregnant women. Reference strains from this facultative intracellular bacterium have been instrumental in the investigation of basic mechanisms in microbiology, immunology, and cell biology.

In prokaryotes, transcription–translation coupling is thought to guarantee the synthesis of high-quality mRNAs and surveil foreign genes. Surprisingly, Johnson et al. show that translation is uncoupled from transcription in Bacillus subtilis, arguing that bacteria utilize very diverse gene expression strategies to meet their unique regulatory needs.

The toxin-producing bacterium Bacillus cereus is an important and neglected human pathogen and a common cause of food poisoning. Several toxins have been implicated in disease, including the pore-forming toxins hemolysin BL (HBL) and nonhemolytic enterotoxin (NHE). Recent work revealed that HBL binds to the mammalian surface receptors LITAF and CDIP1 and that both HBL and NHE induce potassium efflux and activate the NLRP3 inflammasome, leading to pyroptosis.

Host organisms utilize nutritional immunity to limit the availability of nutrients essential to an invading pathogen. Nutrients may include amino acids, nucleotide bases, and transition metals, the essentiality of which varies among pathogens. The mammalian macrophage protein Slc11a1 (previously Nramp1) mediates resistance to several intracellular pathogens. Slc11a1 is proposed to restrict growth of Salmonella enterica serovar Typhimurium in host tissues by causing magnesium deprivation.

As plastic debris in the environment continues to increase, an emerging concern is the potential for microplastic to act as vectors for pathogen transport. With aquaculture the fastest growing food sector, and microplastic contamination of shellfish increasingly demonstrated, understanding any risk of pathogen transport associated with microplastic is important for this industry.

Several intracellular bacterial pathogens, including Listeria monocytogenes, Shigella flexerni, and Rickettsia spp. use an actin-based motility process to spread in mammalian cell monolayers. Cell-to-cell spread is mediated by protrusive structures that contain bacteria encased in the host cell plasma membrane. These protrusions, which form in infected host cells, are internalized by neighboring cells.

Nguyen et al. used transposon sequencing analysis and competitive colonization assays to describe how aspartate/malate can trigger initial Salmonella Typhimurium gut-lumen colonization in mice, providing insight into the significance of certain key metabolites beyond the realm of Salmonella life. Metabolite-driven diagnostic and anti-infective strategies for preventing salmonellosis could rapidly emerge from this work.

Viruses, as obligate intracellular parasites, exploit cellular pathways and resources in a variety of fascinating ways. A striking example of this is the remodelling of intracellular membranes into specialized structures that support the replication of positive-sense ssRNA (+RNA) viruses infecting eukaryotes.

Salmonella enterica is an important gastrointestinal and facultative intracellular pathogen. After invasion of host cells, it resides in a specialized, replication-permissive compartment, the Salmonella-containing vacuole (SCV). During maturation of the SCV, Salmonella remodels the host endosomal system to form a variety of membranous extensions from the SCV, one type designated Salmonella-induced filaments (SIFs).

Interactions between the eukaryotic host, microbiome members, and invading pathogens help to shape disease outcomes. Using the Drosophila model, Fast et al. identified that Vibrio cholerae acts to inhibit epithelial renewal through complex interactions between the type VI secretion system of V. cholerae and the microbial community of the fly.

Vibrio parahaemolyticus is a gram-negative autochthonous bacterium found in temperate and tropical marine and coastal waters globally. V. parahaemolyticus is the most prevalent food-poisoning bacterium associated with seafood consumption, typically causing self-limiting gastroenteritis. V. parahaemolyticus grows preferentially in warm (>15°C), low-salinity marine water (<25 ppt NaCl). Virulent V.

Shigella sonnei is a rod-shaped, Gram-negative facultative intracellular pathogen. It was named ‘Sonne’s bacillus’ after Carl Olaf Sonne who described it as a causative agent of bacillary dysentery. S. sonnei is distributed worldwide and represents the most common cause of shigellosis in industrialized regions in Europe, North America, and Australia. It is currently undergoing expansion in middle-income countries across Asia, Latin America, and the Middle East. S.

Lantibiotic salivaricins are polycyclic peptides containing lanthionine and/or β-methyllanthionine residues produced by certain strains of Streptococcus salivarius, which almost exclusively reside in the human oral cavity. The importance of these molecules stems from their antimicrobial activity towards relevant oral pathogens which has so far been applied through the development of salivaricin-producing probiotic strains.

Espinoza-Vergara et al. unveiled a novel transmission mode of Vibrio cholerae based on environmental protozoan predation, which the bacterial pathogen evades via its release in ‘expelled food vacuoles.’ Vacuole-enclosed bacteria are not only fairly protected against environmental stressors, but also show enhanced intestinal colonization fitness upon oral ingestion.

Vibrio vulnificus is a Gram-negative naturally occurring bacterium found commonly in warm (>15oC), low-salinity/brackish waters worldwide. This bacterium occurs in high numbers in seafood, such as shellfish, particularly in warmer months. V. vulnificus is an important opportunistic pathogen that can cause both wound infections and sepsis, typically via exposure to seawater or through consumption of seafood. V. vulnificus carries the highest case fatality rate of any foodborne pathogen.

Salmonella enterica is a zoonotic pathogen of substantial concern to global human and animal health. It is a leading cause of morbidity and mortality in people worldwide. S. enterica can successfully colonize animals, humans, and plants, and is also found in the environment. Some serovars have a broad host range (S. Typhimurium and S. Enteriditis), others are host-adapted (S. Typhi and S. Paratyphi A and C). Following ingestion, S.

Vibrio cholerae is the bacterial pathogen responsible for the disease cholera, plaguing many developing nations and areas of poor sanitation, and causing about 2.9 million cases and ~95 000 deaths annually. It is transmitted through contaminated water and infects the host using two major virulence factors: the toxin-coregulated pilus (TCP) and cholera toxin (CT).