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The combined effects of ethylenediaminetetraacetic acid (EDTA) and bacteriophage (phage) treatment of foodborne pathogens were investigated. Although viable counts for Campylobacter jejuni decreased by 1.5 log after incubation for 8 h in the presence of phage PC10, re-growth was observed thereafter. The combination of phage PC10 and 1 mM EDTA significantly inhibited the re-growth of C. jejuni. The viable counts for C. jejuni decreased by 2.6 log (P < 0.05) compared with that of the initial count after 24 h. Moreover, EDTA at 0.67 or 1.3 mM, combined with the specific lytic phages, also effectively inhibited the re-growth of phage-resistant cells of Campylobacter coli, Salmonella enterica serovar Enteritidis, and Salmonella enterica serovar Typhimurium. In addition, the combined effects of lytic phages and EDTA were investigated on the viability of Campylobacter in BHI broth at low temperatures followed by the optimum growth temperature. The re-growth of C. coli was significantly inhibited by the coexistence of 1.3 mM EDTA, and the viable counts of surviving bacteria was about the same as the initial viable count after the incubation. This is the first study demonstrating the combined use of lytic phages and EDTA is effective in inhibiting the re-growth of phage-resistant bacteria in Gram-negative bacteria., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The gene encoding LysSTG2, an endolysin from Salmonella-lytic bacteriophage STG2, was cloned, overexpressed, and characterized. LysSTG2 consists of a single domain belonging to the Peptidase&#95;M15 superfamily. LysSTG2 showed strong lytic activity against chloroform-treated S. Typhimurium cells after incubation at 4-50 °C for 30 min, at pH ranging from 7.0 to 11.0, and in the presence of NaCl from 0 to 300 mmol/L. It also showed lytic activity against all the 14 tested Gram-negative strains treated with chloroform, including Salmonella, E. coli, and Pseudomonas aeruginosa, but not against the Gram-positive bacteria tested. In addition, LysSTG2 (100 μg/mL) reduced the viability of S. Typhimurium NBRC 12529 planktonic cells by 1.2 log and that of the biofilm cells after 1-h treatment. Sequential treatment of slightly acidic hypochlorous water (SAHW) containing 40 mg/L available chlorine and LysSTG2 (100 μg/mL) was effective on S. Typhimurium NBRC 12529 biofilm cells, removing more than 99% of biofilm cells. These results demonstrate that LysSTG2 alone can effectively kill S. Typhimurium cells after permeabilization treatment and successfully control S. Typhimurium in biofilms in combination with SAHW, suggesting that the combined use of LysSTG2 and SAHW might be a novel and promising method for combating S. Typhimurium in food industries., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The pathogenicity of Salmonella Typhimurium, a foodborne pathogen, is mainly attributed to its ability to form biofilm on food contact surfaces. ε-polylysine, a polymer of positively charged lysine, is reported to inhibit biofilm formation of both gram-positive and gram-negative bacteria. To elucidate the mechanism underlying ε-polylysine-mediated inhibition of biofilm formation, the transcriptional profiles of ε-polylysine-treated and untreated Salmonella Typhimurium cells were comparatively analysed. The genome-wide DNA microarray analysis was performed using Salmonella Typhimurium incubated with 0.001% ε-polylysine in 0.1% Bacto Soytone at 30 °C for 2 h. The expression levels of genes involved in curli amyloid fibres and cellulose production, quorum sensing, and flagellar motility were downregulated, whereas those of genes associated with colanic acid synthesis were upregulated after treatment with ε-polylysine. The microarray results were validated by quantitative real-time polymerase chain reaction (qRT-PCR). Furthermore, treatment with ε-polylysine decreased the production of colanic acid in Salmonella Typhimurium. The findings of this study improved our understanding of the mechanisms underlying ε-polylysine-mediated biofilm inhibition and may contribute to the development of new disinfectants to control biofilm during food manufacturing and storage.

Salmonella Enteritidis, Salmonella Typhimurium, and Escherichia coli O157:H7 are the most important foodborne pathogens, causing serious food poisoning outbreaks worldwide. Bacteriophages are increasingly considered as novel antibacterial agents to control foodborne pathogens. In this study, 8 Salmonella phages and 10 E. coli O157:H7 phages were isolated from chicken products. A polyvalent phage PS5 capable of infecting S. Enteritidis, S. Typhimurium, and E. coli O157:H7 was further characterized and its efficacy in reducing these foodborne pathogens was evaluated in in vitro and in foods. Morphology, one-step growth, and stability assay showed that phage PS5 was a myovirus, with relatively short latent periods, large burst sizes, and high stability. Genome sequencing analysis revealed that the genome of PS5 does not contain any genes associated to antibiotic resistance, toxins, lysogeny, and virulence factors. In broth, phage PS5 significantly decreased the viable counts of all the three bacterial hosts by more than 1.3 log CFU/mL compared to controls after 2 h of incubation at 4 °C and 24 °C. In foods, treatment with PS5 also resulted in significant reductions of viable counts of all the three bacterial hosts compared to controls at temperatures tested. This is the first report on single phage capable of simultaneously controlling S. Enteritidis, S. Typhimurium and E. coli O157:H7 in both in vitro and in foods., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Mechanisms of recovery from heat injury in Salmonella typhimurium were elucidated. Recovery of the heat-injured S. typhimurium cells in TSB resulted in full recovery after 3 h of incubation at 37°C. The DNA microarray analysis of 30- and 60-min recovering cells resulted in an increase in transcription of 89 and 141 genes, respectively. Among them, 15 genes, with known function, seemed to be somewhat involved in recovery. They encoded proteins involved in branched-chain amino acid (BCAA) transport (livJ, livH), cell envelope integrity (ddg), heat-shock response (cpxP, rrmJ), phage shock protein (pspA), ribosome modulation factor (rmf), virulence (sseB) transcriptional regulation (rpoE, rpoH, rseA, rseB, rseC) and ArcB signal transduction (sixA) and cytoplasmic membrane protein (fxsA). Among them, the effects of BCAA supplementation on recovery from heat injury were studied to confirm the importance of the BCAA transport liv genes during recovery. It was found that supplementation of TSB with 0.1% BCAA resulted in an enhanced recovery of injured cells in comparison to those recovered in TSB without BCAA. Supplementation of BCAA at 0.1% resulted in a cell count increase 4.4-fold greater than that of the control after 1 h incubation. It seems that BCAA promoted the recovery by promoting protein synthesis either directly through their use in translation or indirectly through stimulation of protein synthesis by activation of the Lrp protein.

Chicken meats are considered as main sources associated with Salmonella infections in humans. In this study, lytic phages against Salmonella were isolated and examined for their efficacy to control Salmonella . Eighteen lytic phages were isolated from raw chicken skin and gizzard. Five phages belonging to Myoviridae and Siphoviridae families were characterized and selected for bacterial challenge tests. The treatment of raw chicken breast samples contaminated with S. Enteritidis and S. Typhimurium at 8 °C by the cocktail of five phages significantly reduced ( P  < 0.05) viable counts by 1.41 and 1.86 log CFU/piece, respectively. When incubated at 25 °C, the highest reductions of viable counts of S. Enteritidis and S. Typhimurium in the phage-treated samples were 3.06 and 2.21 log CFU/piece, respectively ( P  < 0.05). These data suggested that the phages isolated from raw chicken meats are potential agents for controlling Salmonella in raw meats. [ABSTRACT FROM AUTHOR]

Salmonella spp., one of the most frequently reported bacteria, causes foodborne illness and economic losses. Due to the threat of increasing antibiotic resistant foodborne pathogens, application of bacteriophages as novel antibacterial agents in food matrices has become an emerging strategy. In this study, a novel Salmonella phage PS3-1 with high lytic activity against Salmonella Typhimurium was identified from previously isolated phages. PS3-1 belonged to the class Caudoviricetes with a broad host range, and had relatively short latent period (15 min), large burst size (92 PFU/cell), high pH stability (pH 3.0–11.0) and thermal tolerance (4–60 °C). Genome sequencing analysis showed that PS3-1 genome consisted of 107,110 bp DNA, without antibiotic resistance and virulence related genes. The results of growth curve and time-kill assay showed that PS3-1 not only inhibited the growth of S. Typhimurium , but also effectively decreased the viable cell counts (0.30–4.72 log) after 24-h incubation at 7, 25 and 37 °C (P < 0.05). Moreover, >1.28 log of established biofilm cells were effectively removed after 24-h treatment with PS3-1. Besides, PS3-1 significantly reduced the viability of S. Typhimurium in milk, lettuce, raw pork meat and ready-to-eat steamed-chicken breast at different temperatures (P < 0.05). These results demonstrated that PS3-1 may be an excellent antibacterial agent for controlling S. Typhimurium in food industry. • Siphoviridae phage PS3-1 showed a rapid and strong lytic activity against Salmonella. • PS3-1 showed great pH tolerance and thermal stability. • PS3-1 significantly removed the S. Typhimurium biofilms with a maximum reduction of 1.52 log at 7 °C. • PS3-1 effectively reduced S. Typhimurium counts in milk, lettuce, raw pork meat and RTE steamed-chicken breast. [ABSTRACT FROM AUTHOR]