Survival rate and detection of human pathogenic bacteria on fresh strawberry

In recent years, the consumption and production of fresh strawberries (Fragaria ananassa) in the U.S has been increasing at a very fast rate. At the same time, food safety relevant to pathogenic contamination that cause food borne illnesses on these fruits has become a major issue from field production through supply chain to consumers.. The main objective of this research was to develop a strategic plan to identify microbial human pathogens (E. coli O157:H7, Salmonella typhimurium and Listeria monocytogenes) on fresh strawberries after stored in refrigerators at 4 °C. For this study, fully mature strawberries were collected from eight U-pick farms and inoculated with three bacterial species (Escherichia coli O157:H7, Salmonella typhimurium and Listeria monocytogenes) and stored at 4°C for 6-7 weeks. Extracts from these stored strawberries were collected and analyzed for the presence of microbial populations using direct spreading and enrichment methods. Antigens from individual inoculated bacterial species, isolated from strawberry extracts were tested against commercially available polyclonal and monoclonal antibodies. These experiments confirmed the presence of bacterial antigens even after long term storage at 4°C. These pathogenic bacterial strains were also inoculated on fresh organic and non-organic strawberries to determine the survival of these pathogenic bacterial strains over time after incubation in refrigerators at (4°C) and at room temperature (25°C). Suspended cultures (7logCFU/mL) of each individual bacterial strains were spot inoculated on the intact surfaces of strawberries and incubated at 4°C and 25°C for one (24 hours), three and five days respectively. Highly significant differences (p\u3c0.05) in bacterial populations were observed in non-organic strawberries inoculated with individual bacterial strains. Overall, initial bacterial populations of all three pathogens on organic strawberries were found to be less. A novel, fast and highly sensitive analysis method, “Dip stick analysis” was developed for the detection of lower inoculum levels of bacterial population on fresh produce. This method was successful in identifying the single bacterial pathogen cells of Salmonella and Listeria is fast, highly sensitive and reliable and can be done by non-scientists for the determination of the status of a strawberry crop for the presence of human pathogen contamination. Taste test surveys were also done to evaluate the consumer’s preference for organic and non-organic strawberries, and also to identify direct-market fresh strawberry customers and their buying behaviors

Effect of Pre-Exposure to Chlorine Dioxide on the Susceptibility of Fecal Coliforms to Antibiotics

Adaptive exposure to sub-lethal concentrations of sanitizers was previously reported to offer cross-protection to bacteria against antibiotics. This study was undertaken to determine whether the pre-exposure of fecal coliforms to suboptimal concentrations of a chemical sanitizer, chlorine dioxide (ClO2), alters their susceptibility to certain antibiotics. Fecal coliforms isolated from fresh fruit packing facilities (n = 12) were adapted in ½ or ¼ of the manufacturer-recommended concentration of ClO2. The susceptibility of the adapted and non-adapted cells to 13 different antibiotics was determined by observing the changes in their minimal inhibitory concentrations (MICs). The results showed that preadaptation to the suboptimal concentrations of ClO2, in general, either decreased or did not change the MICs of the antibiotics against selected fecal coliform isolates, with only two exceptions; preadaptation increased the MICs of kanamycin against two of the fecal coliform isolates, and of nalidixic acid against one of the fecal coliform isolates. The results suggest that the use of ClO2 has a relatively low risk of inducing the resistance of fecal coliforms to antibiotics

Environmental and Fecal Indicator Organisms on Fruit Contact Surfaces and Fruit from Blueberry Mechanical Harvesters

Although previous studies have examined microbial loads on food contact surfaces in blueberry packing plants, there is currently no information regarding microbial risks associated with mechanical berry harvesters used in commercial blueberry production. In this study, we surveyed up to nine fruit contact surfaces on seven mechanical harvesters in each of 2015 and 2016 in the field. These surfaces included the shaking rods at the front of the harvester, the sidewalls of the harvesting tunnel behind the shaking mechanism, the catcher plates collecting the detached berries, horizontal and vertical fruit conveyor belts, and berry lugs collecting the fruit at the back of the harvester. Swab samples were collected from each surface three times a day (morning, noon, and evening) and assessed for environmental and fecal indicator organisms including total aerobes, total yeasts and molds, coliforms and fecal coliforms, and enterococci. At the same time points, fruit samples were assessed for microbial loads before the fruit entered each harvester and after they exited the harvester. Results showed statistically significant differences in microbial loads among harvester surfaces, whereas the effect of sampling time was generally not significant. High levels of total aerobes and total yeasts and molds were recorded, especially on horizontal surfaces and/or those located at the bottom of the harvester such as the lower sidewall, the catcher plates, and the horizontal conveyor belt. These surfaces therefore should be targeted by cleaning and sanitization practices. There was also statistical evidence that passage through the harvester may increase the levels of the environmental microorganisms on fruit in the field. In contrast, fecal indicator organisms such as fecal coliforms and enterococci were detected only sporadically and at very low densities on harvester surfaces and blueberry fruit, and there was no evidence that passage through the harvester increased their levels on the fruit. Berry lugs consistently harbored microbial loads, and given their movement back and forth between the field and the packing plant, deserve particular attention with regard to cleaning, sanitization, and storage protocols

Environmental and Fecal Indicator Organisms on Fruit Contact Surfaces and Fruit from Blueberry Mechanical Harvesters

Although previous studies have examined microbial loads on food contact surfaces in blueberry packing plants, there is currently no information regarding microbial risks associated with mechanical berry harvesters used in commercial blueberry production. In this study, we surveyed up to nine fruit contact surfaces on seven mechanical harvesters in each of 2015 and 2016 in the field. These surfaces included the shaking rods at the front of the harvester, the sidewalls of the harvesting tunnel behind the shaking mechanism, the catcher plates collecting the detached berries, horizontal and vertical fruit conveyor belts, and berry lugs collecting the fruit at the back of the harvester. Swab samples were collected from each surface three times a day (morning, noon, and evening) and assessed for environmental and fecal indicator organisms including total aerobes, total yeasts and molds, coliforms and fecal coliforms, and enterococci. At the same time points, fruit samples were assessed for microbial loads before the fruit entered each harvester and after they exited the harvester. Results showed statistically significant differences in microbial loads among harvester surfaces, whereas the effect of sampling time was generally not significant. High levels of total aerobes and total yeasts and molds were recorded, especially on horizontal surfaces and/or those located at the bottom of the harvester such as the lower sidewall, the catcher plates, and the horizontal conveyor belt. These surfaces therefore should be targeted by cleaning and sanitization practices. There was also statistical evidence that passage through the harvester may increase the levels of the environmental microorganisms on fruit in the field. In contrast, fecal indicator organisms such as fecal coliforms and enterococci were detected only sporadically and at very low densities on harvester surfaces and blueberry fruit, and there was no evidence that passage through the harvester increased their levels on the fruit. Berry lugs consistently harbored microbial loads, and given their movement back and forth between the field and the packing plant, deserve particular attention with regard to cleaning, sanitization, and storage protocols

Relative Cleanability and Sanitization of Blueberry Mechanical Harvester Surfaces

Berry crops are increasingly being harvested mechanically to reduce labor costs, but there is a lack of research on best practices for cleaning and sanitizing of mechanical harvesters to maintain proper food hygiene. Laboratory experiments were conducted with surface coupons cut from materials commonly used on blueberry harvesters, including polyethylene, high-density polyethylene, aluminum, extruded polycarbonate, acetal plastic, and stainless steel. Surfaces differed in their hydrophobicity and surface roughness, ranging from 0.04 µm for polycarbonate to 1.57 µm for acetal plastic. The relative cleanability of the surface coupons was assessed by determining the removal of an applied mock soil (dried blueberry puree) in a rinsing-shaking assay with distilled water at room temperature. Results showed that the amount of soil removed increased over time according to a negative exponential function, from 29.6% at 30 s to 40.3% at 240 s rinse time. Compared with the time effect, the differences in soil removal among surfaces were relatively small. The addition of cleaning agents and detergents did not improve soil removal, and the only treatment that removed significantly more soil than the water control was heated (50 °C) distilled water. In sanitization assays, three representative microorganisms were allowed to attach to surface coupons, then exposed to three different sanitizers (0.25% bleach with 200 ppm free-chlorine sodium hypochlorite, 0.30% SaniDate 5.0, or 1.0% No-Rinse Food Contact Cleaner Sanitizer). There was no significant surface effect on microbial reductions following sanitizer treatment. For Bacillus amyloliquefaciens, none of the sanitizers significantly reduced population densities below the water control. In contrast, surface populations of Rhodoturula mucilaginosa and Epicoccum nigrum were reduced significantly by all three sanitizers, with SaniDate (23.0% hydrogen peroxide + 5.3% peroxyacetic acid) resulting in the greatest reduction

Relative Cleanability and Sanitization of Blueberry Mechanical Harvester Surfaces

Berry crops are increasingly being harvested mechanically to reduce labor costs, but there is a lack of research on best practices for cleaning and sanitizing of mechanical harvesters to maintain proper food hygiene. Laboratory experiments were conducted with surface coupons cut from materials commonly used on blueberry harvesters, including polyethylene, high-density polyethylene, aluminum, extruded polycarbonate, acetal plastic, and stainless steel. Surfaces differed in their hydrophobicity and surface roughness, ranging from 0.04 µm for polycarbonate to 1.57 µm for acetal plastic. The relative cleanability of the surface coupons was assessed by determining the removal of an applied mock soil (dried blueberry puree) in a rinsing-shaking assay with distilled water at room temperature. Results showed that the amount of soil removed increased over time according to a negative exponential function, from 29.6% at 30 s to 40.3% at 240 s rinse time. Compared with the time effect, the differences in soil removal among surfaces were relatively small. The addition of cleaning agents and detergents did not improve soil removal, and the only treatment that removed significantly more soil than the water control was heated (50 °C) distilled water. In sanitization assays, three representative microorganisms were allowed to attach to surface coupons, then exposed to three different sanitizers (0.25% bleach with 200 ppm free-chlorine sodium hypochlorite, 0.30% SaniDate 5.0, or 1.0% No-Rinse Food Contact Cleaner Sanitizer). There was no significant surface effect on microbial reductions following sanitizer treatment. For Bacillus amyloliquefaciens, none of the sanitizers significantly reduced population densities below the water control. In contrast, surface populations of Rhodoturula mucilaginosa and Epicoccum nigrum were reduced significantly by all three sanitizers, with SaniDate (23.0% hydrogen peroxide + 5.3% peroxyacetic acid) resulting in the greatest reduction