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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]

Although conventionally considered an animal pathogen, recent evidence increasingly suggests that fresh produce may act as significant transmission vehicles and alternative hosts to Salmonella. This study reports the differential survivability of two genetically similar Salmonella Thompson strains (ST 889B and ST 688C) on the adaxial surface of pre-harvest basil (Ocimum basilicum) leaves. Upon inoculation, two distinct phenomena, a dried water-print or a macroscopic lesion, were observed within 24 h. ST 889B survived better than ST 688C on healthy-looking leaves without lesions, possibly due to its higher biofilm-forming ability. Both strains survived better on the leaves with lesions than on the healthy-looking leaves (ST 688C: 4.39 ± 0.68 vs. 2.18 ± 0.29; ST 889B: 4.78 ± 0.12 vs. 2.83 ± 0.18 log CFU per sample at 6 days post-inoculation). ST 889B caused the formation of lesions at a higher frequency [70/117 leaves (59.8%)] than ST 688C [35/96 leaves (36.5%)]. Thus, we highlighted two distinct Salmonella survival strategies in the basil pathosystem and demonstrated gene expression polymorphism (variations in the expression of the same set of genes) as an indispensable strategy in the colonization of plants as hosts by the human pathogens. [ABSTRACT FROM AUTHOR]

Human norovirus (HNoVs) and Salmonella are both very important foodborne pathogens with mixed infection of HNoV and Salmonella reported clinically. With the use of model organism zebrafish (Danio rerio), it was observed that the sequential infection of HNoVs and Salmonella caused lower survival rates (12.5 ± 4.2%) than the single-pathogen infection by Salmonella (31.6 ± 7.3%, P < 0.05) or HNoVs (no mortality observed). Gene expression study with the use of RT-PCR and global transcriptomic analysis revealed that the mortality of zebrafish larvae was very likely due to the harmful inflammatory responses. Specifically, it was noted that the genes encoding aconitate decarboxylase 1 (ACOD1), also known as immunoresponsive gene 1 (IRG1), were significantly upregulated in the sequentially infected zebrafish larvae. The expression of acod1 could lead to mitochondrial reactive oxygen species (ROS) production. The ROS levels were indeed higher in sequentially infected zebrafish larvae than the single-pathogen infected ones (P < 0.05). An immersion treatment of glutathione or citraconate did not affect the microbial loads of HNoVs and Salmonella but significantly reduced the ROS levels and protected the zebrafish larvae by inducing higher survival rates in the sequentially infected zebrafish larvae (P < 0.05). Taken together, this study accumulated new knowledge over the function of ACOD1/IRG1 pathway in infectious diseases, and proposed possible treatment strategies accordingly. [ABSTRACT FROM AUTHOR]

Salmonellosis, caused by multidrug-resistant Salmonella species, in particular, is one of the leading notifiable foodborne diseases in Singapore and an emerging public health concern worldwide. The objectives of this study were to determine the prevalence, antibiotic resistance and the presence of gyrA and parC mutations in Salmonella isolated from retail fresh chicken meat in Singapore. A significantly higher prevalence of Salmonella was found in chicken meat from the wet markets (25%, 30/120), as compared to supermarkets (12.7%, 19/150). The top four serovars isolated in this study were S. Saintpaul (32.7%, 17/52), followed by S. Brancaster (21.2%, 11/52), S. Albany (11.5%, 6/52), and S. Stanley (9.6%, 5/52). More than 80% of Salmonella isolates exhibited resistance to at least one of eleven antibiotics tested. The most common phenotypic resistances exhibited were towards ampicillin (78.8%, 41/52), tetracycline and chloramphenicol (61.5%, 32/52), sulfamethoxazole-trimethoprim (55.8%, 29/52) and nalidixic acid (30.8%, 16/52). Of the 52 Salmonella isolates, 59.6% (31/52) were multi-drug resistant strains, resistant to 3 or more antibiotic classes. No mutation in parC gene was found in any of the isolates that expressed phenotypic resistance or reduced susceptibility towards quinolone and/or fluoroquinolone. Mutations at two different sites of gyrA gene were found in 7 isolates, which further discriminates the quinolone resistance genotype in Salmonella isolates from fresh chicken meat. Our findings provide opportunities for risk assessment and management of salmonellosis and antibiotic-resistant Salmonella species in the country and the region. [ABSTRACT FROM AUTHOR]

Singapore in recent years is dedicating great efforts in developing urban agriculture in production of leafy green vegetables. Considering the small scales and diverse set-ups of local farms, it is necessary to collect baseline data to evaluate the microbial safety of local leafy green production. In this study, we collected lettuce crops and agriculture water used in lettuce production from ten different farms (five soil-based farms and five hydroponic farms, 100 samples over a period of five months) and tested with multiple microbial parameters. As a result, 16 out of the 50 agriculture water samples were enumerated with Escherichia coli (4.15 ± 0.81 log CFU/100 ml from 9 samples collected at soil-based farms, 3.79 ± 0.91 log CFU/100 ml from 7 samples collected at hydroponic farms). For the lettuce crops, 7 out of 25 samples from the soil-based farms (with overhead irrigation) were enumerated with an average of 3.28 ± 1.45 log CFU E. coli /g fresh matter, while all of the 25 samples from the hydroponic farms were below 10 CFU E. coli /g fresh matter. Within the 11 Salmonella strains isolated in this study, six strains were from soil-based agriculture water, four strains were from hydroponic agriculture water, only one strain was isolated from lettuce crops and it was from a hydroponic farm. When tested with lettuce crops grown in the laboratory, the five Salmonella isolates from the hydroponic farms showed a higher likelihood of internalization and translocation from the roots to the aerial parts (6/40 [15%] plants tested positive) than the six Salmonella isolates from the soil-based farms (2/48 [4%] plants tested positive). The opportunistic pathogen Stenotrophomonas maltophilia was detected with higher presence at hydroponic farms than the soil-based farms. Antimicrobial resistance (AMR) analysis were performed over all of the Salmonella and S. maltophilia isolates and no AMR strain has been identified so far. Taken together, these results suggested the great needs of both soil-based and hydroponic farms to improve their good agriculture practices such as to implement effective agriculture water treatment and to avoid using overhead irrigation with sprinkler systems. [ABSTRACT FROM AUTHOR]

Fermentation, especially spontaneous fermentation, has become from an ancient food preservation method to a stylish cooking trend in very recent years. Accordingly, the associated food safety should be revisited, particularly since inexperienced people increasingly performing spontaneous fermentation on an ad hoc basis. In this study, three lactic acid bacteria (LAB) strains were tested. Lactiplantibacillus plantarum 299v at high initial inoculation levels (>6 log CFU/mL brine water) effectively eliminated Salmonella spiked in a carrot fermentation system from 4.6 ± 0.2 log CFU/mL to < 1 log CFU/mL after 7 days fermentation at 20 °C. Next, the bacterial enumeration and 16s rRNA gene sequencing results between spontaneous fermentation and fermentation samples using L. plantarum 299v as the starter culture were compared. It was found that the inhibiting effect of L. plantarum 299v could be extended beyond Salmonella spp. to the entire Enterobacteriaceae family during the carrot fermentation. Therefore, our study suggests that in comparison with spontaneous fermentation, selected starter culture such as L. plantarum 299v can consistently improve the safety and quality of fermented foods. • Spontaneous fermentation was compared with fermentation using starter culture. • L. plantarum 299 V as starter culture suppresses Enterobacteriaceae. • L. plantarum 299 V improves the safety and quality of fermented foods. • Probiotics as starter culture increases the health benefits of fermented products. [ABSTRACT FROM AUTHOR]