No abstract

Small-and medium-size farms in the mid-Atlantic region of the United States use varied agricultural practices to produce leafy greens during spring and fall, but the impact of preharvest practices on food safety risk remains unclear. To assess farm-level risk factors, bacterial indicators, Salmonella enterica, and Shiga toxin-producing Escherichia coli (STEC) from 32 organic and conventional farms were analyzed. A total of 577 leafy greens, irrigation water, compost, field soil, and pond sediment samples were collected. Salmonella was recovered from 2.2% of leafy greens (n ‫؍‬ 369) and 7.7% of sediment (n ‫؍‬ 13) samples. There was an association between Salmonella recovery and growing season (fall versus spring) (P ‫؍‬ 0.006) but not farming system (organic or conventional) (P ‫؍‬ 0.920) or region (P ‫؍‬ 0.991). No STEC was isolated. In all, 10% of samples were positive for E. coli: 6% of leafy greens, 18% of irrigation water, 10% of soil, 38% of sediment, and 27% of compost samples. Farming system was not a significant factor for levels of E. coli or aerobic mesophiles on leafy greens but was a significant factor for total coliforms (TC) (P < 0.001), with higher counts from organic farm samples. Growing season was a factor for aerobic mesophiles on leafy greens (P ‫؍‬ 0.004), with higher levels in fall than in spring. Water source was a factor for all indicator bacteria (P < 0.001), and end-of-line groundwater had marginally higher TC counts than source samples (P ‫؍‬ 0.059). Overall, the data suggest that seasonal events, weather conditions, and proximity of compost piles might be important factors contributing to microbial contamination on farms growing leafy greens. Increased awareness of the nutritional and economic benefits of eating fresh produce has caused global consumption to increase 4.5% from 1990 to 2004 (1), but field-grown foods such as vegetables and leafy greens (including lettuce, spinach, spring mix, and kale) can also serve as reservoirs of microorganisms, including bacteria, molds, and yeasts. Most of these microorganisms are not harmful and are part of the background microflora of the plant. However, human-pathogenic bacteria such as Salmonella, Listeria monocytogenes, Shigella spp., and Escherichia coli O157:H7 have been associated with foodborne outbreaks involving fresh produce (2). The ability of foodborne pathogens to colonize and persist as part of the plant microbiome as endophytes or epiphytes (reviewed in reference 3) represents a significant food safety risk, as fresh produce is often consumed raw without any processing "kill step."In the United States, estimates calculate approximately 4.9 million yearly incidents of food-related illnesses attributed to plant commodities, with leafy vegetables comprising 22.3% of these (4). Following the E. coli O157:H7 multistate outbreak in fall 2006, which was attributed to spinach (5), leafy greens have received significant attention from government, industry, and academic researchers. Other incidents have implicated leafy greens as a vehicl...

No abstract

This study compared the automated BAX PCR with the standard culture method (SCM) to detect Listeria monocytogenes in blue crab processing plants. Raw crabs, crabmeat, and environmental sponge samples were collected monthly from seven processing plants during the plant operating season, May through November 2006. For detection of L. monocytogenes in raw crabs and crabmeat, enrichment was performed in Listeria enrichment broth, whereas for environmental samples, demi-Fraser broth was used, and then plating on both Oxford agar and L. monocytogenes plating medium was done. Enriched samples were also analyzed by BAX PCR. A total of 960 samples were examined; 59 were positive by BAX PCR and 43 by SCM. Overall, there was no significant difference (P ≤0.05) between the methods for detecting the presence of L. monocytogenes in samples collected from crab processing plants. Twenty-two and 18 raw crab samples were positive for L. monocytogenes by SCM and BAX PCR, respectively. Twenty and 32 environmental samples were positive for L. monocytogenes by SCM and BAX PCR, respectively, whereas only one and nine finished products were positive. The sensitivities of BAX PCR for detecting L. monocytogenes in raw crabs, crabmeat, and environmental samples were 59.1, 100, and 60%, respectively. The results of this study indicate that BAX PCR is as sensitive as SCM for detecting L. monocytogenes in crabmeat, but more sensitive than SCM for detecting this bacterium in raw crabs and environmental samples.

No data exist on the impact of cultivation practices on food safety risks associated with cucumber. Cucumbers are typically grown horizontally over a mulch cover, with fruit touching the ground, but this vining plant grows well in vertical systems. To assess whether production system affects bacterial dispersal onto plants, field trials were conducted over 2 years. Cucumber cultivar 'Marketmore 76' was grown horizontally on plastic, straw, or bare ground or vertically on trellises installed on bare ground in soil previously amended with raw dairy manure. Fruit, flower, leaf, and soil samples were collected to quantify Escherichia coli , thermotolerant coliforms, and enterococci by direct plating. E. coli isolates were characterized by BOX-PCR to evaluate relatedness among strains. Although thermotolerant coliforms and enterococci were significantly less abundant on fruit in year 1 (P < 0.05), this result was not seen in year 2 when more rain was recorded. Instead, fruit from straw-mulched beds had higher levels of enterococci compared with fruit grown on bare ground (P < 0.05). Leaves on bare ground occasionally had more bacteria than did leaves on plastic mulch beds (P < 0.05). Production system did not impact flower-associated bacterial levels. E. coli isolates (n =127) were genotyped, generating 21 distinct fingerprints. Vertical production did not appear to be a barrier for E. coli dispersal to the crop, as suggested by numerous related isolates from soil and flowers on bare ground, straw-mulched, and trellised beds (subcluster B1). None of the isolates from soil and flowers in this subcluster were related to isolates recovered from fruit, showing that flower colonization does not necessarily lead to fruit colonization. One cluster of isolates contained those from flowers and fruits but not soil, indicating a source other than manure-amended soil. Straw may be a source of E. coli ; a number of closely related E. coli isolates were retrieved from soil and fruits from straw-mulched beds. Our approach revealed E. coli dispersal patterns and could be used to assess bacterial transmission in other production systems.