Few microbial studies in aquaponics, a growing trend in food production, have been conducted to determine food safety status. The aim of this study was to determine the food safety status and the effectiveness of ultraviolet treatment (15 W, luminous flux of 900 lm) as a food safety intervention in reducing the microbial loads of the water system in a model aquaponic unit growing lettuce, basil, and barramundi (Australian Sea Bass). Sweet basil, bibb lettuce, water samples, and fish swabs were collected throughout the 118-day production period, and microbial analysis was conducted in triplicate for the presence of E. coli O157:H7, Salmonella spp., and the prevalence of aerobic plate counts (APC), coliforms, and fecal coliforms in these systems. Absence of foodborne pathogens was confirmed using ELISA technology and enumeration through petrifilms (coliform/E. coli). A significant increase was observed in aerobic plate counts over the trial period (1 to 3 log 10 CFU·mL −1 ) in the presence and absence of UV (p > 0.05). Ultraviolet treatment did not significantly reduce the APC or coliform counts when compared to the control system samples. Future work should focus on improving the unit design, the evaluation of bio-solid filtration, and other food safety interventions.

Over the past few years, foodborne disease outbreaks linked to enteric pathogens present on cantaloupe and watermelon surfaces have raised concerns in the melon industry. This research evaluated the effectiveness of commercially available produce sanitizers against selected foodborne pathogens, both in cell suspensions and on the outer rind surface of melons. The sanitizers (65 and 200 ppm of chlorine, 5 and 35% hydrogen peroxide, 5 and 50 ppm of liquid chlorine dioxide, various hydrogen peroxide-acid combinations, 0.78 and 2.5% organic acids, and 300 ppm of quaternary ammonium) were tested against Escherichia coli O157:H7, Listeria monocytogenes, Salmonella, and non-O157 Shiga toxin-producing E. coli (O26, O45, O103, O111, O121, and O145). The cell suspension study revealed the ability of all tested sanitizers to reduce all selected pathogens by 0.6 to 9.6 log CFU/ml in vitro. In the melon study, significant differences in pathogen reduction were observed between sanitizers but not between melon types. The most effective sanitizers were quaternary ammonium and hydrogen peroxide-acid combinations, with 1.0- to 2.2-log CFU/g and 1.3- to 2.8-log CFU/g reductions, respectively, for all pathogens. The other sanitizers were less effective in killing the pathogens, with reductions ranging from 0.0 to 2.8 log CFU/g depending on pathogen and sanitizer. This study provides guidance to the melon industry on the best produce sanitizers for use in implementing a broad-spectrum pathogen intervention strategy.

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Increased popularity of natural and organic processed meats can be attributed to the growing consumer demand for preservative-free foods, including processed meats. To meet this consumer demand, meat processors have begun using celery juice concentrate in place of sodium nitrite to create products labeled as no-nitrate or no-nitrite-added meat products while maintaining the characteristics unique to conventionally cured processed meats. Because of flavor limitations, natural cures with celery concentrate typically provide lower ingoing nitrite concentrations for ready-to-eat processed meats than do conventional cures, which could allow for increased growth of pathogens, such as Clostridium perfringens, during cooked product cooling such as that required by the U.S. Department of Agriculture. The objective of this study was to investigate the implications associated with reduced nitrite concentrations for preventing C. perfringens outgrowth during a typical cooling cycle used for cooked products. Nitrite treatments of 0, 50, and 100 ppm were tested in a broth system inoculated with a three-strain C. perfringens cocktail and heated with a simulated product thermal process followed by a typical cooling-stabilization process. The nitrite concentration of 50 ppm was more effective for preventing C. perfringens outgrowth than was 0 ppm but was not as effective as 100 ppm. The interaction between nitrite and temperature significantly affected (P < 0.05) C. perfringens outgrowth in both total population and number of vegetative cells. Both temperature and nitrite concentration significantly affected (P < 0.05) C. perfringens spore survival, but the interaction between nitrite and temperature did not have a significant effect (P > 0.05) on spore outgrowth. Results indicate that decreased nitrite concentrations (50 ppm) have increased potential for total C. perfringens population outgrowth during cooling and may require additional protective measures, such as faster chilling rates.

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Nonendospore-forming pathogenic bacteria in the long-term survival (LTS) phase can remain viable for months or years and may show reduced susceptibility to various antimicrobial interventions. In the present study, we investigated the response of LTS phase Salmonella enterica serovar Typhimurium (ATCC 14028) to ultraviolet (UV) radiation in 0.85% (w/v) saline and apple juice and the extent of sublethal injury in LTS phase survivors. The LTS-phase Salmonella Typhimurium cells were cultured at 35°C for 14 days in tryptic soy broth with 0.6% (w/v) yeast extract (TSBYE). Exponential- and stationary-phase cells, cultured in TSBYE (35°C) for 2.5 and 18 h, respectively, served as control samples. Cells (10 CFU [colony-forming unit]/mL) from each physiological state were exposed to UV light in saline (80 μW/cm) and apple juice (1500 μW/cm). The Salmonella Typhimurium survivors were plated for enumeration on either tryptic soy agar with 0.6% yeast extract or xylose-lysine-tergitol 4 (XLT4) agar and colonies counted after incubation (35°C, 24 h). Of all the growth phases tested, LTS phase cells were consistently impacted the least by UV treatment (p < 0.05). In saline, D-values of exponential, stationary, and LTS Salmonella Typhimurium were 0.35, 0.38, and 0.49 min, respectively. D-values in apple juice at pH 3.63 and pH 5.65 were 2.52, 3.19, and 3.57 min and 3.24, 3.50, and 4.18 min, respectively. UV radiation (80 μW/cm) of Salmonella Typhimurium in saline for 2.5 min reduced the number of exponential- and stationary-phase cells by ∼7.19 and 6.30 log CFU/mL, respectively. In contrast, LTS cells were only reduced by 5.08 log CFU/mL. Among the three physiological states, LTS phase cells had the least sublethal injury in the surviving population (p < 0.05). These results indicate that the LTS state cross-protects Salmonella Typhimurium against UV radiation and should be considered in determination of the UV radiation D-value for this pathogen.

Tildipirosin (TIP) is a novel 16-membered-ring macrolide authorized for the treatment of bovine and swine respiratory disease. The pH dependency of macrolide antimicrobial activity is well known. Considering that the pH in the colon contents of growing beef cattle and pigs is usually below pH 7.0, the minimum inhibitory concentrations (MIC) of TIP against foodborne bacterial pathogens such as Campylobacter (C.) coli, C. jejuni and Salmonella enterica and commensal species including Enterococcus (E.) faecalis, E. faecium and Escherichia coli were determined under standard (pH 7.3 ± 1) or neutral as well as slightly acidic conditions. A decrease in pH from 7.3 to 6.7 resulted in an increase in MICs of TIP. Except for the MICs > 256 μg/mL observed in the resistant subpopulation of the C. coli and the Enterococcus species, the MIC ranges increased from 2-8 μg/mL to 64-> 256 μg/mL for Salmonella enterica and E. coli, from 8-16 μg/mL to 32-128 μg/mL for the two Campylobacter species, and from 4-32 μg/mL to 128-> 256 μg/mL for both Enterococcus species. To estimate the antimicrobial activity of TIP in the colon contents of livestock during recommended usage of the parenterally administered TIP (Zuprevo(®) ), and to compare this with the increased MICs at the slightly acidic colonic pH, we developed and validated a microbiological assay for TIP and used this to test incurred faecal samples collected from cattle and pigs. Microbiological activity of luminal TIP was determined in aqueous supernatants from diluted faeces, using standard curves produced from TIP-spiked faecal supernatants. The limit of quantification (LOQ) for TIP was 1 μg/mL (ppm). In a cattle study (n = 14), 3 of 28 faecal samples collected 24 and 48 h post-treatment were found to contain TIP above the LOQ (concentrations of 1.3-1.8 ppm). In another cattle study (n = 12) with faecal samples collected at 8, 24 and 48 h post-treatment, TIP concentrations were above the LOQ in 4 of the 8 h samples (1.2-2.6 ppm) and one of the 24-h samples (1.3 ppm). In a pig study (n = 12) with faecal samples collected 24, 48 and 72 h post-treatment, only one sample contained TIP above the LOQ (concentration 1.5 ppm). In another pig study (n = 12), with samples collected at 8, 24 48 and 96 h post-treatment, TIP concentrations were above the LOQ in one 8-h sample (1.1 ppm) and two 24-h samples (2.3 and 2.5 ppm). None of the 48-h and 96-h samples from these 4 studies contained measurable TIP concentrations. Thus, in cattle and pigs, only a small fraction of faecal samples collected up to 24 h postdosing contained measurable microbiologically active TIP, with its maximum limited to 2.6 μg/mL. This is several log2 dilution steps below the MICs of TIP against foodborne pathogens and commensals collected under acidic conditions comparable with those in the colonic contents and may explain a lack of intestinal dysbacteriosis with parenteral tildipirosin in livestock.