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Aims This study aims to investigate the in vitro pathogenicity of Chromobacterium haemolyticum strain WI5 toward the intestinal tract, its resistance to water treatments, and its potential for foodborne transmission through leafy greens produced in hydroponic systems. Methods and results C. haemolyticum WI5 caused cytopathic effects in human colon cells HCT116 and exhibited an 8.2-fold higher cell attachment compared to Salmonella serotype Typhimurium. It showed comparable resistance to sodium hypochlorite (NaOCl) and ultraviolet (UV) treatments as Escherichia coli O157: H7 and Pseudomonas aeruginosa but was more susceptible to desiccation. On lettuce, C. haemolyticum WI5 failed to persist, with counts decreasing below the detection limit (≥4 log reductions) after 3 and 2 days at 4 and 25°C, respectively. Conclusions C. haemolyticum WI5 demonstrated considerable virulence features and high in vitro pathogenicity toward the intestinal tract. NaOCl and UV treatments were effective in disinfecting C. haemolyticum in water. Due to its high susceptibility to desiccation and poor survivability on lettuce, the foodborne transmission potential of C. haemolyticum is considered limited. [ABSTRACT FROM AUTHOR]

Aims: We investigated the fate of Salmonella in lettuce seeds grown in a hydroponic system and the potentials of applying photodynamic inactivation (PDI) to enhance microbial safety of hydroponic farming systems. Methods and Results: Lettuce was grown from Salmonella‐contaminated seeds, and rose bengal‐mediated PDI was applied. Without intervention, Salmonella could persist in plants and hydroponic farming environment throughout 6 weeks of lettuce growth. Cross‐contamination from Salmonella‐inoculated to noninoculated seedlings was observed. PDI significantly decreased Salmonella from 3.90 ± 0.31 log colony‐forming unit (CFU) per plant to 2.77 ± 0.49 log CFU per plant without extra illumination needed (p < 0.01) by week six. Conclusions: Salmonella from contaminated seeds could survive for an extended period in lettuce and hydroponic farming environment and posed serious cross‐contamination risks. Rose bengal‐mediated PDI showed promise in controlling Salmonella contamination in lettuce in a hydroponic farming setting. Significance and Impact of the Study: This study shed light on the serious food safety implications that Salmonella‐contaminated lettuce seeds might entail in a hydroponic farming environment and demonstrated rose bengal‐mediated PDI as a potential mitigation strategy. These findings contribute to the increasingly relevant field of urban farming systems and their associated food safety concerns. [ABSTRACT FROM AUTHOR]

Group B Streptococcus (GBS) was previously not known to be transmitted through food, but an outbreak investigation in Singapore in 2015 documented for the first time an association between GBS Type III Sequence Type 283 infection and consumption of raw fish dishes. As very little is known about the survival of GBS during heat treatment and the stomach transit, its survival under simulated conditions was studied, in comparison with that of Escherichia coli O157:H7 and Listeria monocytogenes. The mean D-values of four GBS strains ranging from 0.72 to 0.88 min in neutral pH tryptone soy broth at 56.4 °C and 0.44–1.43 min at pH 2.35 at 37 °C in simulated gastric fluid, were significantly lower (p < 0.05) than those of E. coli O157:H7 and L. monocytogenes. This study suggests possible factors other than acid or heat resistance of GBS to be instrumental to its pathogenicity. [ABSTRACT FROM AUTHOR]

Background: Salmonella enterica subspecies enterica serovar Saintpaul (S. Saintpaul) is an important gut pathogen which causes salmonellosis worldwide. Although intestinal salmonellosis is usually self-limiting, it can be life-threatening in children, the elderlies and immunocompromised patients. Appropriate antibiotic treatment is therefore required for these patients. However, the efficacy of many antibiotics on S. enterica infections has been greatly compromised due to spreading of multidrug resistance (MDR) plasmids, which poses serious threats on public health and needs to be closely monitored. In this study, we sequenced and fully characterized an S. enterica MDR plasmid pSGB23 isolated from chicken. Results: Complete genome sequence analysis revealed that S. Saintpaul strain SGB23 harbored a 254 kb megaplasmid pSGB23, which carries 11 antibiotic resistance genes responsible for resistance to 9 classes of antibiotics and quaternary ammonium compounds that are commonly used to disinfect food processing facilities. Furthermore, we found that pSGB23 carries multiple conjugative systems, which allow it to spread into other Enterobacteriaceae spp. by self-conjugation. It also harbors multiple types of replicons and plasmid maintenance and addictive systems, which explains its broad host range and stable inheritance. Conclusions: We report here a novel MDR plasmid pSGB23 harboured by S. enterica. To our knowledge, it carried the greatest number of antibiotic resistance genes with the broadest range of resistance spectrum among S. enterica MDR plasmids identified so far. The isolation of pSGB23 from food sources is worrisome, while surveillance on its further spreading will be carried out based on the findings reported in this study. [ABSTRACT FROM AUTHOR]

This study performed microbial analysis of nutrient film technique (NFT) hydroponic systems on three indoor farms in Singapore (the "what"). To justify the necessity of sanitizing hydroponic systems, strong biofilm-forming bacteria were isolated from the facility and investigated for their influence on Salmonella colonization on polyvinyl chloride (PVC) coupons in hydroponic nutrient solutions (the "why"). Finally, sanitization solutions were evaluated with both laboratory-scale and field-scale tests (the "how"). As a result, the microbiome composition in NFT systems was found to be highly farm specific. The strong biofilm formers Corynebacterium tuberculostearicum C2 and Pseudoxanthomonas mexicana C3 were found to facilitate the attachment and colonization of Salmonella on PVC coupons. When forming dual-species biofilms, the presence of C2 and C3 also significantly promoted the growth of Salmonella ( P < 0.05). Compared with hydrogen peroxide (H 2 O 2 ) and sodium percarbonate (SPC), sodium hypochlorite (NaOCl) exhibited superior efficacy in biofilm removal. At 50 ppm, NaOCl reduced the Salmonella Typhimurium, C2, and C3 counts to <1 log CFU/cm 2 within 12 h, whereas neither 3% H 2 O 2 nor 1% SPC achieved this effect. In operational hydroponic systems, the concentration of NaOCl needed to achieve biofilm elimination increased to 500 ppm, likely due to the presence of organic matter accumulated during crop cultivation and the greater persistence of naturally formed multispecies biofilms. Sanitization using 500 ppm NaOCl for 12 h did not impede subsequent plant growth, but chlorination byproduct chlorate was detected at high levels in the hydroponic solution and in plants in the sanitized systems without rinsing., Importance: This study's significance lies first in its elucidation of the necessity of sanitizing hydroponic farming systems. The microbiome in hydroponic systems, although mostly nonpathogenic, might serve as a hotbed for pathogen colonization and thus pose a risk for food safety. We thus explored sanitization solutions with both laboratory-scale and field-scale tests. Of the three tested sanitizers, NaOCl was the most effective and economical option, whereas one must note the vital importance of rinsing the hydroponic systems after sanitization with NaOCl., Competing Interests: The authors declare no conflict of interest.