Prior exposure of agriculture cephalosporin ceftiofur impaired conjugation of blaCTX-M-65 gene-bearing plasmid in Salmonella Saintpaul.

AIMS: Although a link between agricultural cephalosporin use and resistance in Salmonella has been demonstrated with the drug ceftiofur, the underlying mechanism of the correlation is unclear. This study investigated the impact of ceftiofur exposure in S. Saintpaul on ceftriaxone resistance, the gene expression and the conjugative transfer of the blaCTX-M-65 gene. METHODS AND RESULTS: Prior ceftiofur exposure caused a twofold increase in MIC from 1024 to 2048 µg ml-1 towards ceftriaxone and increased the enzymatic activity of BlaCTX-M-65 2·2 folds from 3·46 to 7·67 nmol nitrocefin hydrolysed min-1 . A threefold upregulation in gene expression of the blaCTX-M-65 gene was also observed. Donors exposed to ceftiofur subsequently demonstrated a 2·5-fold decrease in transfer efficiency. CONCLUSIONS: Prior exposure of S. Saintpaul to ceftiofur led to increased phenotypic resistance towards ceftriaxone while its ability to spread the cephalosporin resistance through conjugation, conversely, was impaired. SIGNIFICANCE AND IMPACT OF THE STUDY: Findings from this study shed light on one possible mechanism in which agricultural cephalosporin exposure in Salmonella may subsequently impact clinical treatment. The finding that cephalosporin exposure in donors may hinder the subsequent spread of resistance instead of aiding it up was counter-intuitive.

Biofilm formation and disinfectant resistance of Salmonella sp. in mono- and dual-species with Pseudomonas aeruginosa.

AIMS: This study aimed to evaluate the biofilm formation and disinfectant resistance of Salmonella cells in mono- and dual-species biofilms with Pseudomonas aeruginosa, and to investigate the role of extracellular polymeric substances (EPS) in the protection of biofilms against disinfection treatment. METHODS AND RESULTS: The populations of Salmonella in mono- or dual-species biofilms with P. aeruginosa on stainless steel (SS) coupons were determined before and after exposure to commercial disinfectant, 50 µg ml-1 chlorine or 200 µg ml-1 Ecolab® Whisper™ V (a blend of four effective quaternary ammonium compounds (QAC)). In addition, EPS amount from biofilms was quantified and biofilm structures were observed using scanning electron microscopy (SEM). Antagonistic interactions between Salmonella and P. aeruginosa resulted in lower planktonic population level of Salmonella, and lower density in dual-species biofilms compared to mono-species biofilms. The presence of P. aeruginosa significantly enhanced disinfectant resistance of S. Typhimurium and S. Enteritidis biofilm cells for 2 days, and led to an average of 50% increase in polysaccharides amount in dual-species biofilms than mono-species biofilms of Salmonella. Microscopy observation showed the presence of large microcolonies covered by EPS in dual-species biofilms but not in mono-species ones. CONCLUSION: The presence of P. aeruginosa in dual-species culture inhibited the growth of Salmonella cells in planktonic phase and in biofilms, but protected Salmonella cells in biofilms from disinfection treatment, by providing more production of EPS in dual-species biofilms than mono-species ones. SIGNIFICANCE AND IMPACT OF THE STUDY: This study provides insights into inter-species interaction, with regard to biofilm population dynamics and disinfectant resistance. Thus, a sanitation protocol should be designed considering the protective role of secondary species to pathogens in biofilms on SS surface which has been widely used at food surfaces and manufacturers.

Antibacterial efficacy of 405, 460 and 520 nm light emitting diodes on Lactobacillus plantarum, Staphylococcus aureus and Vibrio parahaemolyticus.

AIMS: Little information is available on a direct comparison of the antibacterial efficacy of light emitting diode (LEDs) of different peak wavelengths. Thus, the objective of this study was to evaluate the effect of LEDs of three different wavelengths on bacterial inactivation. METHODS AND RESULTS: Lactobacillus plantarum, Staphylococcus aureus and Vibrio parahaemolyticus were illuminated with 405, 460 and 520 nm LEDs at 4, 10 and 25°C respectively. Inactivation curves were plotted and fitted using Gompertz Model. Illumination with 405 and 460 nm LED produced significant inactivation (P < 0·05) in the population of V. parahaemolyticus (>4 log) while Lact. plantarum and Staph. aureus showed relatively less susceptibility to the LED illumination. The 520 nm LED produced negligible inactivation. CONCLUSIONS: The 405 and 460 nm LEDs proved more effective in inactivating the selected foodborne bacteria in this study compared to 520 nm LED. The 405 nm LED showed the greatest antibacterial effect at the same level of energy dose. SIGNIFICANCE AND IMPACT OF THE STUDY: The results in this study demonstrated the antibacterial efficacy of 405 nm LED on Lact. plantarum and V. parahaemolyticus, suggesting its potential for use in food industry for the control of these micro-organisms.

Adaptation of Salmonella spp. in juice stored under refrigerated and room temperature enhances acid resistance to simulated gastric fluid.

The objective of this study was to evaluate the acid resistance of Salmonella spp. adapted in juices stored under refrigeration and room temperatures to simulated gastric fluid (SGF, pH 1.5). Five Salmonella serovars, Agona, Gaminara, Michigan, Montevideo, and Poona were used in this study. Apple, orange, and tomato juices inoculated with five serovars were stored at refrigeration (7 degrees C) and room temperature (20 degrees C) for 24 h for adaptation. Acid resistances of serovars adapted in juice were determined in SGF at 37 degrees C. All acid-adapted Salmonella serovars in juices displayed enhanced survival time compared to non-adapted controls. Among serovars, S. Poona adapted in apple at 20 degrees C and orange juices at 7 and 20 degrees C showed >2.0 log cfu/ml survivors, while the other serovars decreased to non-detectable level or <2.0 log cfu/ml for 100 s in SGF. Unlike apple and orange juices, all serovars adapted in tomato juice survived with >2.0 log cfu/ml for 100 s. For D-values, all Salmonella serovars adapted in apple and tomato juice enhanced their acid resistances compared to orange juices. S. Agona adapted in tomato juice at 7 degrees C and S. Poona in apple juice at 20 degrees C had the highest D-values with 82.9 and 82.5s, respectively. Results showed that the adaptation in juice increased acid resistance in SGF and varied by serovar, juice type, and adaptation temperature. Therefore, this study indicates that the introduction of Salmonella spp. to an acidic juice environment during processing can enhance their ability to survive in a human stomach, possibly increasing the risk of a Salmonella outbreak by juice.