Nutrition & Food Science
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Item Rapid detection of Salmonella in food and feed by coupling loop-mediated isothermal amplification with bioluminescent assay in real-time(Springer Nature, 2016-06-17) Yang, Qianru; Domesle, Kelly J; Wang, Fei; Ge, BeileiSalmonella is among the most significant pathogens causing food and feed safety concerns. This study examined the rapid detection of Salmonella in various types of food and feed samples by coupling loop-mediated isothermal amplification (LAMP) with a novel reporter, bioluminescent assay in real-time (BART). Performance of the LAMP-BART assay was compared to a conventional LAMP and the commercially available 3M Molecular Detection Assay (MDA) Salmonella. The LAMP-BART assay was 100 % specific among 178 strains (151 Salmonella and 27 non-Salmonella) tested. The detection limits were 36 cells per reaction in pure culture and 104 to 106 CFU per 25 g in spiked food and feed samples without enrichment, which were comparable to those of the conventional LAMP and 3M MDA Salmonella but 5–10 min faster. Ground turkey showed a strong inhibition on 3M MDA Salmonella, requiring at least 108 CFU per 25 g for detection. The correlation between Salmonella cell numbers and LAMP-BART signals was high (R 2 = 0.941–0.962), suggesting good quantification capability. After 24 h enrichment, all three assays accurately detected 1 to 3 CFU per 25 g of Salmonella among five types of food (cantaloupe, ground beef, ground turkey, shell eggs, and tomato) and three types of feed (cattle feed, chicken feed, and dry dog food) examined. However, 101 CFU per 25 g was required for cattle feed when tested by 3M MDA Salmonella. The Salmonella LAMP-BART assay was rapid, specific, sensitive, quantitative, and robust. Upon further validation, it may become a valuable tool for routine screening of Salmonella in various types of food and feed samples.Item EVALUATION OF THE BEHAVIOR OF SALMONELLA ENTERICA IN REHYDRATED DRY DOG FOODS(2017) Qu, Yinzhi; Pradhan, Abani K; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Recent human salmonellosis outbreaks associated with dry dog foods have raised concern over these products as potential vehicles for Salmonella. In this study, different behavior (decline or growth) of Salmonella across twenty-six different brand dog foods that were rehydrated to a moisture content of 35% and stored at 30°C for 72 hr were characterized. Decline data were fitted with log-linear model and growth data were fitted by reparameterized Gompertz model. The distributions for the parameters in the fitted reparameterized Gompertz model were obtained. The effects of pH and water activity of rehydrated dog foods on changes in Salmonella levels (Log CFU/g) within 72 hr were modeled by the second order polynomial regression. The results can be implemented in the future quantitative microbial risk assessment studies. This study was useful in providing critical information regarding Salmonella and dog food to develop effective contamination prevention and mitigation strategies.Item Antimicrobial Resistance of Salmonella and E. coli from Pennsylvania Dairy Herds(2015) Cao, Huilin; Pradhan, Abani K.; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The emergence and dissemination of bacterial antimicrobial resistance has become a major public health concern. A total of 444 manure composite samples were collected from 80 dairy farms in Pennsylvania, representing pre-weaned calves, post-weaned calves, dry cows, and lactating cows. E. coli and Salmonella were isolated, and tested for antimicrobial susceptibility. Salmonella was isolated from at least one sample from 51 (64%) farms and was more prevalent in adult animals than young animals. The predominant serotypes were Cerro, Montevideo and Kentucky. Salmonella isolates were mostly susceptible to all antimicrobials. E. coli were commonly resistant to tetracycline, streptomycin, sulfisoxazole and ampicillin. Resistance of up to 8 classes of antibiotics was observed in E. coli isolated from young animals. The blaCMY- and blaCTX-M-carrying E. coli were detected in 35% and 5% of the farms, respectively. The presence of multi-drug resistant E. coli suggested potential risks to human health associated with dairy farming.Item Investigating Metrics Proposed to Prevent the Harvest of Leafy Green Crops Contaminated by Floodwater(2015) Callahan, Mary Theresa; Buchanan, Robert L; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Pathogens can be transported by water through soil to contaminate distant crops. The California LGMA states that leafy green crops within 30ft of flooded soil should be destroyed due to potential contamination. Previously flooded areas should not be replanted for 60 days. This study investigated the transport of Salmonella enterica and Citrobacter freundii through soil in a model system with a positive slope (uphill). Field trials involving flooding one end of a spinach bed with a negative slope (downhill) with water containing Escherichia coli were also conducted. Soil type, soil moisture content, and slope affected bacterial movement. In field trials, E. coli was quickly transported to the 30ft boundary, and persisted significantly longer in the fall trial than the spring. These data suggest the LGMA metrics need to provide additional parameters to prevent the harvest of leafy green crops potentially contaminated by floodwater.Item ALTERNATIVE APPROACHES IN MOLECULAR CHARACTERIZATION OF FOODBORNE PATHOGENS: SHIGA TOXIN-PRODUCING Escherichia coli AND Salmonella SEROTYPES(2014) Toro Ibaceta, Magaly Alejandra; Meng, Jianghong; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Shiga toxin-producing E. coli (STEC) and Salmonella enterica subspecies enterica (S. enterica) are two major foodborne pathogens. They cause almost 1.5 million of cases of disease each year in the US. Due to their public health impact, development of new methods for their detection and identification are top priority. This research focused on identifying alternative molecular methods and markers for the identification of STEC and Salmonella. First, a suspension array was developed to simultaneously identify the seven most prevalent STEC (O26, O45, O103, O111, O121, O145, and O157) in the US. The panel targeted genes wzx or wzy and Shigatoxin genes. Testing and optimization employed four to eleven isolates of each serotype in the panel. STEC fluorescence values were 30 to >270 times greater than those of negative controls, demonstrating the method's effectiveness for the molecular serotyping of STEC. STEC strains (n=194) of 43 serotypes were examined for clustered regularly interspaced short palindromic repeats (CRISPR) arrays to study relatedness among serotypes. A subset of strains (n=81) was analyzed for cas and virulence genes to determine a possible relationship. CRISPR spacer content correlated well with serotypes, although some strains with different serogroup but the same H type shared identical arrays (O26:H11, O103:H11, and O111:H11). cas and virulence genes were not associated, but strains with greater probability of causing outbreaks and disease showed fewer spacers than those less likely to cause them (p<0.05). Therefore, CRISPR array content correlated well with STEC serotype, and CRISPR-cas systems were inversely related to strain virulence potential. Finally, the CRISPR arrays of 221 S. enterica of 53 serotypes were analyzed to define their relationship. CRISPR-cas systems of 50 S. enterica serotype Bareilly (S. Bareilly) were analyzed to resolve intra-serotype variations. CRISPR arrays correlated well with serotypes, although some serotypes displayed more than one type of array (e.g. S. Bareilly). Additionally, CRISPR-cas system elements reflected S. Bareilly phylogeny, but the array content was not linked to food vehicle or isolate's geographical origin. In conclusion, CRISPR array are useful for designing molecular serotyping assays, but a range of strains should be included to account for variation in S. enterica.Item The Role of Organic Matrices (dried turkey manure) in the Contamination and Survival of Salmonella spp. on Baby Spinach Leaves(2012) Oni, Ruth Adeola; Buchanan, Robert L; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Microbiological safety of fresh produce has attracted attention due to constant produce outbreaks. Manure contaminated with enteric pathogens has been identified as a major pre-harvest contamination source. This study investigated the survival of Salmonella in dust particles generated from dehydrated turkey manure, and how this could serve as an airborne contamination of leafy greens. Laboratory trials of the UV resistance of Salmonella in manure dust were also conducted to assess its protective effect; along with greenhouse studies to determine the survival of Salmonella in manure dust on spinach leaves. Results indicate survival times were inversely related to moisture content and particle size of manure dust. The presence of manure particles substantially enhanced the pathogen's survival under UV and reduced its inactivation on spinach leaves. This study presents data that could be used to assess the potential role of aerosolized manure as a pre-harvest risk factor for contamination of leafy greens.Item Intervention Strategies for Escherichia coli O157:H7 and Salmonella in Organic Soil and on Fresh Produce(2012) Nguekam Yossa, Irene Nadine; Lo, Martin; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Recently, foodborne diseases caused by Escherichia coli O157:H7 and Salmonella have been increasingly associated with the consumption of fresh produce. Consumers' demand for safe, natural products has led to research on natural antimicrobials for effective control of foodborne pathogens on fresh produce, which can be inadvertently contaminated by soil. Therefore, there is a need to control microbial loads in soil to minimize contamination. The objectives of this study were to evaluate the antimicrobial activity of cinnamaldehyde, Ecotrol®, eugenol, Sporan® and acetic acid against E. coli O157:H7 and Salmonella in organic soil, and to evaluate the antimicrobial effects of cinnamaldehyde and Sporan® alone, or in combination with acetic acid against E. coli O157:H7, Salmonella, and the native microflora of iceberg, romaine and spinach leaves. The quality parameters of the treated fresh produce were monitored, whereas the modes of action of cinnamaldehyde and Sporan® were investigated. The results showed that cinnamaldehyde had the highest bactericidal activity against E. coli O157:H7 and Salmonella in organic soil. Increases in oil concentration resulted in further reduction of both microorganisms. Up to 5 and 6 log CFU/g of E. coli O157:H7 and Salmonella, respectively, were reduced with 2% Sporan® and acetic acid after 24 h. Sporan® in combination with acetic acid (1000SV) and 800 ppm cinnamaldehyde-Tween reduced significantly E. coli O157:H7 (~3 log CFU/g) on iceberg and spinach leaves following treatment at day 0. Likewise, 1000SV treatment reduced Salmonella ~ 2.5 log CFU/g at day 0. E. coli O157:H7 and Salmonella populations in treated iceberg, spinach and romaine leaves were reduced during storage at 4°C. The native microflora of untreated and treated spinach and lettuce leaves increased during the storage time. The texture and the color of iceberg, romaine and spinach leaves treated with essential oils were not significantly different from the control lettuce after 14 days. The scanning and transmission electron microscopy of oil-treated bacterial cells indicated possible cell structural damage and leakage of cellular content. This study shows the potential use of essential oils to effectively reduce E. coli O157:H7 and Salmonella populations in soil and on fresh produce without adversely affecting leaf color and texture.