Preharvest Food Safety: What Do the Past and the Present Tell Us About the Future?

Innovative Treatments Enhancing the Functionality of Gut Microbiota to Improve Quality and Microbiological Safety of Foods of Animal Origin

The gastrointestinal tract, or gut, microbiota is a microbial community containing a variety of microorganisms colonizing throughout the gut that plays a crucial role in animal health, growth performance, and welfare. The gut microbiota is closely associated with the quality and microbiological safety of foods and food products originating from animals. The gut microbiota of the host can be modulated and enhanced in ways that improve the quality and safety of foods of animal origin. Probiotics—also known as direct-fed microbials—competitive exclusion cultures, prebiotics, and synbiotics have been utilized to achieve this goal. Reducing foodborne pathogen colonization in the gut prior to slaughter and enhancing the chemical, nutritional, or sensory characteristics of foods (e.g., meat, milk, and eggs) are two of many positive outcomes derived from the use of these competitive enhancement–based treatments in food-producing animals.

Expected final online publication date for the Annual Review of Food Science and Technology, Volume 13 is March 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

A four-season longitudinal study of enterohaemorrhagic Escherichia coli in beef cow-calf herds in Mississippi and Nebraska

Our objective was to describe the probability of detecting seven serogroups of enterohaemorrhagic Escherichia coli (EHEC-7) of public health importance in faecal samples from beef cow-calf herds and to test for factors associated with their detection. Fresh faecal samples (n = 85) from two Mississippi and two Nebraska herds were collected in each of four seasons. Samples were tested for each EHEC-7 serogroup by a molecular screening assay. Separate management groups within herds were sampled, and group-level factors were recorded. To measure the effects of factors on faecal shedding of EHEC-7, separate multivariable logistic regression models were used, accounting for the random effect of clustering by group within farm. Statistical significance was set α = 0.05. Fifty-nine samples (4.3%) were positive for EHEC O26, and Nebraska samples were more likely to be positive than Mississippi samples (OR = 12.4, 95% CI: 1.1, 139.2). Forty-four samples (3.2%) were positive for EHEC O45. Odds for detection were greater in the summer than all other seasons combined (OR = 4.2, 95% CI: 1.3, 14.0), and odds decreased if a precipitation event occurred (OR = 0.07, 95% CI: 0.006, 0.8). EHEC O103 was detected in 66 samples (4.9%) with increased probability to be detected at increased temperature. EHEC O111 was detected in 71 samples (5.2%), and 43 samples (3.2%) were positive for EHEC O145. Both EHEC O111 and O145 were associated separately with season, with greater probability for detection in the summer. Eighteen (1.3%) and 68 (5.0%) samples were positive for EHEC O121 and EHEC O157, respectively. We failed to detect significant explanatory factors associated with probability to detect EHEC O121 or O157. Factors that vary by time and place, such as precipitation, ambient temperature, region and season, are uniquely associated with the probability to detect EHEC-7 in fresh faeces collected from cow-calf herds.

Reducing Foodborne Pathogen Persistence and Transmission in Animal Production Environments: Challenges and Opportunities

Preharvest strategies to reduce zoonotic pathogens in food animals are important components of the farm-to-table food safety continuum. The problem is complex; there are multiple pathogens of concern, multiple animal species under different production and management systems, and a variety of sources of pathogens, including other livestock and domestic animals, wild animals and birds, insects, water, and feed. Preharvest food safety research has identified a number of intervention strategies, including probiotics, direct-fed microbials, competitive exclusion cultures, vaccines, and bacteriophages, in addition to factors that can impact pathogens on-farm, such as seasonality, production systems, diet, and dietary additives. Moreover, this work has revealed both challenges and opportunities for reducing pathogens in food animals. Animals that shed high levels of pathogens and predominant pathogen strains that exhibit long-term persistence appear to play significant roles in maintaining the prevalence of pathogens in animals and their production environment. Continued investigation and advancements in sequencing and other technologies are expected to reveal the mechanisms that result in super-shedding and persistence, in addition to increasing the prospects for selection of pathogen-resistant food animals and understanding of the microbial ecology of the gastrointestinal tract with regard to zoonotic pathogen colonization. It is likely that this continued research will reveal other challenges, which may further indicate potential targets or critical control points for pathogen reduction in livestock. Additional benefits of the preharvest reduction of pathogens in food animals are the reduction of produce, water, and environmental contamination, and thereby lower risk for human illnesses linked to these sources.

Shiga toxin-producing Escherichia coli distribution and characterization in a pasture-based cow-calf production system

Shiga toxin-producing Escherichia coli (STEC) strains are commonly found in cattle gastrointestinal tracts. In this study, prevalence and distribution of E. coli virulence genes (stx1, stx2, hlyA, and eaeA) were assessed in a cow-calf pasture-based production system. Angus cows (n = 90) and their calves (n = 90) were kept in three on-farm locations, and fecal samples were collected at three consecutive times (July, August, and September 2011). After enrichment of samples, stx1, stx2, eaeA, and hlyA were amplified and detected with a multiplex PCR (mPCR) assay. Fecal samples positive for stx genes were obtained from 93.3% (84 of 90) of dams and 95.6% (86 of 90) of calves at one or more sampling times. Age class (dam or calf), spatial distribution of cattle (farm locations B, H, K), and sampling time influenced prevalence and distribution of virulence genes in the herd. From 293 stx-positive fecal samples, 744 E. coli colonies were isolated. Virulence patterns of isolates were determined through mPCR assay: stx1 was present in 41.9% (312 of 744) of the isolates, stx2 in 6.5% (48 of 744), eaeA in 4.2% (31 of 744), and hlyA in 2.4% (18 of 744). Prevalence of non-O157 STEC was high among the isolates: 33.8% (112 of 331) were STEC O121, 3.6% (12 of 331) were STEC O103, and 1.8% (6 of 331) were STEC O113. One isolate (0.3%) was identified as STEC O157. Repetitive element sequence-based PCR (rep-PCR) fingerprinting was used to study genetic diversity of stx-positive E. coli isolates. Overall, rep-PCR fingerprints were highly similar, supporting the hypothesis that strains are transmitted between animals but not necessarily from a dam to its calf. Highly similar STEC isolates were obtained at each sampling time, but isolates obtained from dams were more diverse than those from calves, suggesting that strain differences in transference may exist. Understanding the transfer of E. coli from environmental and animal sources to calves may aid in developing intervention strategies to reduce E. coli colonization of young cattle.