Survival and Transmission of Salmonella enterica Serovar Typhimurium in an Outdoor Organic Pig Farming Environment

U.S. salmonellosis outbreaks have occurred following consumption of tomato and cantaloupe but not lettuce. We report differential contamination among agricultural seedlings by Salmonella enterica via soil. Members of the family Brassicaceae had a higher incidence of outbreak than carrot, lettuce, and tomato. Once they were contaminated, phyllosphere populations were similar, except for tomato. Contamination differences exist among tomato cultivars.Other than disease outbreaks caused by sprouted seeds, salmonellosis outbreaks associated with fresh produce have been attributed most frequently to consumption of tomatoes (6, 7), followed by consumption of cantaloupes (4). Although contamination of leafy greens by Shiga toxin-producing Escherichia coli has caused food-borne illness (8), outbreaks attributed to Salmonella enterica contamination of leafy greens have not been reported in the United States and are rare worldwide, except for those occurring in the United Kingdom (1,13,21,22). Research to date has not addressed this discrepancy between those crops associated with salmonellosis; thus, we examined the ability of S. enterica to colonize agricultural crops seeded in contaminated soil, a probable route of preharvest contamination (5).Enriched potting soil (total nitrogen, 0.14%; available P 2 O 5 , 0.09%; soluble potash, K 2 O 0.02%; total iron, 0.25%; Canadian sphagnum peat moss, ground fir bark, compost, and sand in a proprietary blend) at a pH of 5.5 to 6.5 was irrigated once with an S. enterica suspension containing a mixture of eight strains from fresh produce salmonellosis outbreaks. Bacteria were struck from frozen stock and grown overnight on LuriaBertani-kanamycin medium (40 mg/liter) plates at 37°C. Equal numbers (10 4 CFU/ml) of the S. enterica serovars Baildon 05x-02123 (9), Cubana 98A9878 (20) (14), Poona 00A3563 (CHD, cantaloupe outbreak), and Schwarzengrund 96E01152C (14) comprised the bacterial suspension in sterile water. To verify that the black colonies recovered from Salmonella-Shigella agar with kanamycin (SS-Kan, 50 g/ml) were inoculated strains, each strain was transformed with pKT-Kan, a broad-host-range vector that confers kanamycin resistance and green fluorescent protein expression (19). This plasmid has been shown to have no effect on the survival and growth of S. enterica on plants (2). Twenty-four hours later, surfacesanitized seeds (2) were sown in the contaminated soil, and pots were kept in a controlled environment growth chamber under a day-and-night cycle of 12 h, during which the day temperature was 26°C and the night temperature was 18°C, similar to that of an average spring season in northern California, and humidity was constant at 75%. Pots were irrigated every other day with 25 ml of sterile water, which resulted in no drainage.Preliminary experiments revealed no differences among rhizoplane S. enterica populations on different plants (data not shown). Thus, only the phyllosphere was sampled at the one true leaf stage, as previously described (3). Seed germination was si...

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confidence: 74%

Differential Attachment to and Subsequent Contamination of Agricultural Crops by Salmonella enterica

Barak

Liang

Narm

2008

“…Higher prevalence of Salmonella in pigs during the final stages of production is of greater concern from a public health and food safety perspective. Only a few studies have been conducted to highlight the prevalence of Salmonella in the ABF environment versus that in the conventional farm environment (6,7,9,32). In the ABF farm environment, Salmonella was detected only in three feed and two water samples at nursery 1 and finishing stages, in contrast to the conventional farm, for which positive environmental samples were widely represented by water, soil, feed, floor swabs, lagoon, and truck at different stages of production.…”

Section: Discussionmentioning

confidence: 99%

Longitudinal Study of Distributions of Similar Antimicrobial-Resistant Salmonella Serovars in Pigs and Their Environment in Two Distinct Swine Production Systems

Keelara

Scott

Morrow

et al. 2013

The aim of this longitudinal study was to determine and compare the prevalences and genotypic profiles of antimicrobial-resistant (AR) Salmonella isolates from pigs reared in antimicrobial-free (ABF) and conventional production systems at farm, at slaughter, and in their environment. We collected 2,889 pig fecal and 2,122 environmental (feed, water, soil, lagoon, truck, and floor swabs) samples from 10 conventional and eight ABF longitudinal cohorts at different stages of production (farrowing, nursery, finishing) and slaughter (postevisceration, postchill, and mesenteric lymph nodes [MLN]). In addition, we collected 1,363 carcass swabs and 205 lairage and truck samples at slaughter. A total of 1,090 Salmonella isolates were recovered from the samples; these were isolated with a significantly higher prevalence in conventionally reared pigs (4.0%; n ‫؍‬ 66) and their environment (11.7%; n ‫؍‬ 156) than in ABF pigs (0.2%; n ‫؍‬ 2) and their environment (0.6%; n ‫؍‬ 5) (P < 0.001). Salmonella was isolated from all stages at slaughter, including the postchill step, in the two production systems. Salmonella prevalence was significantly higher in MLN extracted from conventional carcasses than those extracted from ABF carcasses (P < 0.001). We identified a total of 24 different serotypes, with Salmonella enterica serovar Typhimurium, Salmonella enterica serovar Anatum, Salmonella enterica serovar Infantis, and Salmonella enterica serovar Derby being predominant. The highest frequencies of antimicrobial resistance (AR) were exhibited to tetracycline (71%), sulfisoxazole (42%), and streptomycin (17%). Multidrug resistance (resistance to >3 antimicrobials; MDR) was detected in 27% (n ‫؍‬ 254) of the Salmonella isolates from the conventional system. Our study reports a low prevalence of Salmonella in both production systems in pigs on farms, while a higher prevalence was detected among the carcasses at slaughter. The dynamics of Salmonella prevalence in pigs and carcasses were reciprocated in the farm and slaughter environment, clearly indicating an exchange of this pathogen between the pigs and their surroundings. Furthermore, the phenotypic and genotypic fingerprint profile results underscore the potential role played by environmental factors in dissemination of AR Salmonella to pigs.

“…Many researchers have reported that soil microbial communities respond to the presence of heavy metals and organic pollutants (1)(2)(3)(4)(5)(6). Increasing numbers of studies in recent years have also been conducted on soil biopollution by pathogenic microorganisms, including viruses, protozoa, and bacteria such as Escherichia coli O157:H7, Salmonella spp., and Listeria monocytogenes (7)(8)(9). E. coli O157: H7, a significant pathogen carried naturally by animals, has been shown to pose a significant threat to environmental safety and public health because of its low infective dose (as few as 10 cells) and its high pathogenicity in watery diarrhea, hemorrhagic colitis, hemorrhagic-uremic syndrome, thrombotic thrombocytopenic purpura, etc.…”

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confidence: 99%

Interaction between the Microbial Community and Invading Escherichia coli O157:H7 in Soils from Vegetable Fields

Yao

Wang

et al. 2014

The survival of Escherichia coli O157:H7 in soils can contaminate vegetables, fruits, drinking water, etc. However, data on the impact of E. coli O157:H7 on soil microbial communities are limited. In this study, we monitored the changes in the indigenous microbial community by using the phospholipid fatty acid (PLFA) method to investigate the interaction of the soil microbial community with E. coli O157:H7 in soils. Simple correlation analysis showed that the survival of E. coli O157:H7 in the test soils was negatively correlated with the ratio of Gram-negative (G ؊ ) to Gram-positive (G ؉ ) bacterial PLFAs (G ؊ /G ؉ ratio). In particular, levels of 14 PLFAs were negatively correlated with the survival time of E. coli O157:H7. The contents of actinomycetous and fungal PLFAs in the test soils declined significantly (P, <0.05) after 25 days of incubation with E. coli O157:H7. The G ؊ /G ؉ ratio declined slightly, while the ratio of bacterial to fungal PLFAs (B/F ratio) and the ratio of normal saturated PLFAs to monounsaturated PLFAs (S/M ratio) increased, after E. coli O157:H7 inoculation. Principal component analysis results further indicated that invasion by E. coli O157:H7 had some effects on the soil microbial community. Our data revealed that the toxicity of E. coli O157:H7 presents not only in its pathogenicity but also in its effect on soil microecology. Hence, close attention should be paid to the survival of E. coli O157:H7 and its potential for contaminating soils.