Planar Interdigitated Aptasensor for Flow-Through Detection of Listeria spp. in Hydroponic Lettuce Growth Media

Irrigation water is a primary source of fresh produce contamination by bacteria during the preharvest, particularly in hydroponic systems where the control of pests and pathogens is a major challenge. In this work, we demonstrate the development of a Listeria biosensor using platinum interdigitated microelectrodes (Pt-IME). The sensor is incorporated into a particle/sediment trap for the real-time analysis of irrigation water in a hydroponic lettuce system. We demonstrate the application of this system using a smartphone-based potentiostat for rapid on-site analysis of water quality. A detailed characterization of the electrochemical behavior was conducted in the presence/absence of DNA and Listeria spp., which was followed by calibration in various solutions with and without flow. In flow conditions (100 mL samples), the aptasensor had a sensitivity of 3.37 ± 0.21 kΩ log-CFU−1 mL, and the LOD was 48 ± 12 CFU mL−1 with a linear range of 102 to 104 CFU mL−1. In stagnant solution with no flow, the aptasensor performance was significantly improved in buffer, vegetable broth, and hydroponic media. Sensor hysteresis ranged from 2 to 16% after rinsing in a strong basic solution (direct reuse) and was insignificant after removing the aptamer via washing in Piranha solution (reuse after adsorption with fresh aptamer). This is the first demonstration of an aptasensor used to monitor microbial water quality for hydroponic lettuce in real time using a smartphone-based acquisition system for volumes that conform with the regulatory standards. The aptasensor demonstrated a recovery of 90% and may be reused a limited number of times with minor washing step

Genomic and Phenotypic Analysis of Salmonella enterica Bacteriophages Identifies Two Novel Phage Species

Bacteriophages (phages) are potential alternatives to chemical antimicrobials against pathogens of public health significance. Understanding the diversity and host specificity of phages is important for developing effective phage biocontrol approaches. Here, we assessed the host range, morphology, and genetic diversity of eight Salmonella enterica phages isolated from a wastewater treatment plant. The host range analysis revealed that six out of eight phages lysed more than 81% of the 43 Salmonella enterica isolates tested. The genomic sequences of all phages were determined. Whole-genome sequencing (WGS) data revealed that phage genome sizes ranged from 41 to 114 kb, with GC contents between 39.9 and 50.0%. Two of the phages SB13 and SB28 represent new species, Epseptimavirus SB13 and genera Macdonaldcampvirus, respectively, as designated by the International Committee for the Taxonomy of Viruses (ICTV) using genome-based taxonomic classification. One phage (SB18) belonged to the Myoviridae morphotype while the remaining phages belonged to the Siphoviridae morphotype. The gene content analyses showed that none of the phages possessed virulence, toxin, antibiotic resistance, type I–VI toxin–antitoxin modules, or lysogeny genes. Three (SB3, SB15, and SB18) out of the eight phages possessed tailspike proteins. Whole-genome-based phylogeny of the eight phages with their 113 homologs revealed three clusters A, B, and C and seven subclusters (A1, A2, A3, B1, B2, C1, and C2). While cluster C1 phages were predominantly isolated from animal sources, cluster B contained phages from both wastewater and animal sources. The broad host range of these phages highlights their potential use for controlling the presence of S. enterica in foods

Novel off-flavors produced from the thermophillic bacteria, Alicyclobacillus acidoterrestris, in pineapple juice

International audienc

Novel off-flavors produced from the thermophillic bacteria, Alicyclobacillus acidoterrestris, in pineapple juice

International audienc

Salmonella transfer potential between tomatoes and cartons used for distribution

Corrugated fiberboard boxes (cartons) can be reused during fresh market tomato packing and repacking. The fate of Salmonella on the new, used, and dirty tomato packaging cartons, and Salmonella transfer between tomatoes and new, used, and dirty packaging cartons was assessed. Mature green tomatoes or blank cartons were spot inoculated with cocktail of rifampicin-resistant Salmonella strains before touching cartons/tomatoes at 0, 1, or 24 h postinoculation. Tomatoes were placed on new, used, and dirty carton squares (5 by 5 cm) for 0, 1, and 7 days of contact at 12°C and 25°C with a relative humidity value of 85%. Transfer coefficients (TCs) were calculated for all conditions. Salmonella populations decreased following inoculation by 2–3 log units during 24 h drying regardless of storage temperature; the presence of debris enhanced survival at 12°C. In general, the highest transfer rates occurred with wet inoculum. The highest Salmonella transfer was calculated for wet inoculated tomatoes with 7 days of contact time at 25°C (TC = 14.7). Increasing contact time decreased TCs for new cartons, but increased TCs for used and dirty cartons. Regardless of carton condition or storage temperature, a greater population of Salmonella was transferred from tomatoes to cartons than from cartons to tomatoes. Salmonella transfer between tomatoes and cartons is highly dependent on moisture, with increased levels of moisture increasing transfer, highlighting the importance of harvesting and packing dry tomatoes

Modeling and Statistical Issues Related to \u3ci\u3eSalmonella\u3c/i\u3e in Low Water Activity Foods

The presence and survival of Salmonella in low water activity (aw) foods continues to pose a challenge for the food industry. Peer‐reviewed literature data on prevalence and levels of contamination of Salmonella in low water activity foods in the United States are limited. Available published data include those on: Salmonella contamination on nuts and peanuts (Calhoun et al., 2013), almonds (Danyluk et al., 2007; Bansal et al., 2010), pecans (Brar, Strawn, and Danyluk, 2016), and walnuts (Davidson et al., 2015); prevalence and levels of Salmonella on spices (Van Doren et al., 2013); as well as data on prevalence of Salmonella in animal feed (Li et al., 2012). On the other hand, data on survival and inactivation of Salmonella in low water activity foods have been collected extensively. Examples include Salmonella in a wide variety of nuts (Uesugi, Danyluk, and Harris, 2006; Uesugi and Harris, 2006; Danyluk et al., 2008; Beuchat and Mann, 2010, 2011; Abd, McCarthy, and Harris, 2012; Blessington, Mitcham, and Harris, 2012, 2014; Kimber et al., 2012; Beuchat et al., 2013b; Blessington et al., 2013a; Blessington et al., 2013b; Brar et al., 2015), whey protein (Santillana Farakos, Frank, and Schaffner, 2013), peanut butter (Ma et al., 2009; Lathrop, Taylor, and Schnepf, 2014; Li, Huang, and Chen, 2014), dry confectionary raw materials (Komitopoulou and Penaloza, 2009), spices (Keller et al., 2013), and several others as detailed in the reviews by FAO/WHO (2014), Beuchat et al. (2013a) and Podolak et al. (2010). In these studies, Salmonella is shown to be very resistant to desiccation and, once the cells are dry, have an increased resistance to heat. A high degree of variability is seen among studies, substrates, and the environmental conditions under which the experiments take place. Water activity is one critical factor in Salmonella inactivation and survival. Other influencing factors include the interaction between water and Salmonella cells and the effect of temperature, as well as the interaction between water and other components of the food matrix (e.g., sugars and fats). How these factors and interactions influence survival is still not well understood

Microbial quality of agricultural water in Central Florida

<div><p>The microbial quality of water that comes into the edible portion of produce is believed to directly relate to the safety of produce, and metrics describing indicator organisms are commonly used to ensure safety. The US FDA Produce Safety Rule (PSR) sets very specific microbiological water quality metrics for agricultural water that contacts the harvestable portion of produce. Validation of these metrics for agricultural water is essential for produce safety. Water samples (500 mL) from six agricultural ponds were collected during the 2012/2013 and 2013/2014 growing seasons (46 and 44 samples respectively, 540 from all ponds). Microbial indicator populations (total coliforms, generic <i>Escherichia coli</i>, and enterococci) were enumerated, environmental variables (temperature, pH, conductivity, redox potential, and turbidity) measured, and pathogen presence evaluated by PCR. <i>Salmonella</i> isolates were serotyped and analyzed by pulsed-field gel electrophoresis. Following rain events, coliforms increased up to 4.2 log MPN/100 mL. Populations of coliforms and enterococci ranged from 2 to 8 and 1 to 5 log MPN/100 mL, respectively. Microbial indicators did not correlate with environmental variables, except pH (<i>P</i><0.0001). The <i>invA</i> gene (<i>Salmonella</i>) was detected in 26/540 (4.8%) samples, in all ponds and growing seasons, and 14 serotypes detected. Six STEC genes were detected in samples: <i>hly</i> (83.3%), <i>fliC</i> (51.8%), <i>eaeA</i> (17.4%), <i>rfbE</i> (17.4%), <i>stx-</i>I (32.6%), <i>stx-</i>II (9.4%). While all ponds met the PSR requirements, at least one virulence gene from <i>Salmonella</i> (<i>invA-</i>4.8%) or STEC (<i>stx-</i>I-32.6%, <i>stx-</i>II-9.4%) was detected in each pond. Water quality for tested agricultural ponds, below recommended standards, did not guarantee the absence of pathogens. Investigating the relationships among physicochemical attributes, environmental factors, indicator microorganisms, and pathogen presence allows researchers to have a greater understanding of contamination risks from agricultural surface waters in the field.</p></div

Precipitation and microbial indicator correlations for all ponds.

<p>Precipitation and microbial indicator correlations for all ponds.</p