Cronobacter species, in particular C. sakazakii, is an opportunistic bacterial pathogen implicated in the development of potentially debilitating illnesses in infants (<12months old). The combination of a poorly developed immune system and gut microbiota put infants at a higher risk of infection compared to other age groups. Probiotics and prebiotics are incorporated in powdered infant formula and, in addition to strengthening gut physiology and stimulating the growth of commensal gut microbiota, have proven antimicrobial capabilities. Postbiotics in the cell-free supernatant of a microbial culture are derived from probiotics and can also exert health benefits. Synbiotics, a mixture of probiotics and prebiotics, may provide further advantages as probiotics and gut commensals degrade prebiotics into short-chain fatty acids that can provide benefits to the host. Cell-culture and animal models have been widely used to study foodborne pathogens, but sophisticated gut models have been recently developed to better mimic the gut conditions, thus giving a more accurate representation of how various treatments can affect the survival and pathogenicity of foodborne pathogens. This review aims to summarize the current understanding on the connection between Cronobacter infections and infants, as well as highlight the potential efficacy of probiotics, prebiotics, and synbiotics in reducing invasive Cronobacter infections during early infancy.

Sprouts are the leading cause of foodborne disease outbreaks globally, mainly because the specialized conditions required to germinate seed sprouts for human consumption contribute to an environment that allows pathogenic bacteria to flourish. To reduce risk of illness, current food safety guidelines in the United States and Canada recommend hypochlorite treatment for seed sanitation. However, many growers and consumers have become wary of the impact of hypochlorite on human health and the environment and are actively seeking less caustic approaches. Here, we evaluated the effects of both the traditional hypochlorite treatment and a milder alternative on nontyphoidal Salmonella enterica colonization of germinating alfalfa seed. Moreover, we explored three biological factors as potential contributors for inhibition of S. enterica growth: colonization by indigenous bacteria, seed composition changes, and seed metabolite release. In this experimental setting, we found that a combinatorial treatment of heat, peroxide, and acetic acid was as effective as hypochlorite for inhibiting S. enterica growth. Notably, we pinpointed N-acetyl-spermidine as an endogenous metabolite exuded by treated seeds that strongly inhibits S. enterica growth. In doing so, we both elucidated one of the mechanisms of chemical sanitation and highlighted a potential seed-derived mode of antimicrobial treatment that may apply to modernized food safety protocols. IMPORTANCE Warm, humid, and nutrient-rich conditions that are used to produce sprouts encourage Salmonella enterica to proliferate. However, many disparate sanitation methods exist, and there is currently no single treatment that can guarantee pathogen-free seeds. Here, we compared the ability of traditional hypochlorite treatment against a combinatorial treatment of heat, peroxide, and vinegar (HPA) commonly used in organic farming practices to inhibit S. enterica colonization and growth during alfalfa germination and found HPA to be at least as effective. Furthermore, we explored seed-based changes following sanitization treatments using metabolomics and identified polyamines as strong inhibitors of Salmonella growth on germinating alfalfa. Our findings enable a better understanding of host-pathogen interactions in sprout microbial communities and promote in-depth, evidence-based research in seed sprout safety.

Powdered infant formula (PIF) can be contaminated with Cronobacter sakazakii, which can cause severe illnesses in infants. Synbiotics, a combination of probiotics and prebiotics, could act as an alternative control measure for C. sakazakii contamination in PIF and within the infant gut, but synbiotics have not been well studied for their ability to inhibit C. sakazakii. Using a Simulator of the Human Intestinal Microbial Ecosystem (SHIME®) inoculated with infant fecal matter, we demonstrated that a potential synbiotic, consisting of six lactic acid bacteria (LAB) strains and Vivinal GOS, can inhibit the growth of C. sakazakii in an infant possibly through either the production of antimicrobial metabolites like acetate, increasing species diversity within the SHIME compartments to compete for nutrients or a combination of mechanisms. Using a triple SHIME set-up, i.e., three identical SHIME compartments, the first SHIME (SHIME 1) was designated as the control SHIME in the absence of a treatment, whereas SHIME 2 and 3 were the treated SHIME over 2, 1-week treatment periods. The addition of the potential synbiotic (LAB + VGOS) resulted in a significant decrease in C. sakazakii levels within 1 week (p < 0.05), but in the absence of a treatment the significant decline took 2 weeks (p < 0.05), and the LAB treatment did not decrease C. sakazakii levels (p ≥ 0.05). The principal component analysis showed a distinction between metabolomic profiles for the control and LAB treatment, but similar profiles for the LAB + VGOS treatment. The addition of the potential synbiotic (LAB + VGOS) in the first treatment period slightly increased species diversity (p ≥ 0.05) compared to the control and LAB, which may have had an effect on the survival of C. sakazakii throughout the treatment period. Our results also revealed that the relative abundance of Bifidobacterium was negatively correlated with Cronobacter when no treatments were added (ρ = −0.96; p < 0.05). These findings suggest that C. sakazakii could be inhibited by the native gut microbiota, and inhibition can be accelerated by the potential synbiotic treatment.

Cronobacter sakazakii is an opportunistic foodborne pathogen that can be fatal to infants and is commonly associated with powdered infant formula due to contamination in manufacturing processes, hospitals, or homes. This project aimed to select a potential synbiotic, a combination of probiotic strains with a prebiotic product, to inhibit the growth of C.sakazakii in an in vitro dynamic infant gut model (Simulator of the Human Intestinal Microbial Ecosystem). A total of 16 lactic acid bacteria (LAB) were tested for their inhibitory properties against four different C. sakazakii strains by a zone of inhibition test. Lactobacillus and Pediococcus species were able to inhibit the growth (>15-mm inhibition zones) of all C. sakazakii strains tested and only one strain from the two genera exhibited atypical resistance to tetracycline. All C. sakazakii strains and the selected LAB strains, which inhibited C. sakazakii and did not exhibit atypical antibiotic resistance, were grown in Luria-Bertani or MRS broth, respectively, containing 1% dextrose or 1% commercial prebiotic (w/v) to compare their ability to metabolize the prebiotic product. Overall, based on the growth inhibition of C. sakazakii , antibiotic susceptibility, and prebiotic metabolism, 6 out of the 16 LAB were chosen to be part of a potential synbiotic. This study has provided valuable information that will help with the development of a synbiotic that can be used in powdered infant formula to reduce the potential for C. sakazakii related illnesses in infants.