SF6036 - Evaluation of the Ability of a Seaweed Extract (Tasco-14) to Reduce the Duration and Intensity of Fecal Shedding of Escherichia coli 0157:H7 and Total E. coli by Cattle
Dr. Tim McAllister, Agriculture and Agri-Food Canada, Lethbridge
Summary of Research Results:
Food-borne diseases caused by Escherichia coli O157:H7 are frequently traced back to meat products from cattle or to cattle production systems. Over 100 cases of E. coli O157:H7 infections were recorded in the Canadian disease surveillance system in 2005. Many of the more recent outbreaks of E. coli O157:H7 have been associated with environmental sources of E. coli O157:H7 as opposed to direct consumption of meat that has been contaminated with the pathogen. Therefore, if the risk of outbreak is to be reduced, strategies must be developed to mitigate this bacterium during cattle production as well as during meat processing.
Considerable research has been dedicated to developing strategies to reduce the prevalence of E. coli O157:H7 in beef production systems. Technologies presently in development include vaccines, administration of chlorate-based sterilizers, and inoculation of cattle with bacteria intended to prevent establishment of E. coli O157:H7 in the bovine digestive tract. None of these has been 100% effective, however, and it is becoming increasingly clear that a "tool box" of mitigation technologies and management practices are required for real progress to be made in reducing the on-farm prevalence of this pathogen.
From a Canadian perspective, one of the most interesting approaches in the battle against E. coli O157:H7 involves the Northern Atlantic seaweed, Ascophyllum nodosum. This seaweed grows in the Maritimes and has a broad range of applications, including the manufacture of cosmetics and even food products, such as ice cream. Acadian Seaplants Ltd., based in Nova Scotia, collects and processes the seaweed into a product named Tasco-14, which has attracted a great deal of interest in its use as a feed additive for livestock. Tasco-14 was first studied for its antioxidant activities and its ability to improve the health of livestock and extend the shelf life of meat productions. A research group at Texas Tech University was the first to show that Tasco-14 may alter the diet in a manner that reduces the establishment and the shedding of E. coli O157: H7 from the digestive tract of cattle. The Texas study was conducted at a commercial feedlot using cattle that were naturally infected with E. coli O157:H7. Although it showed that Tasco-14 offered promise as a method of mitigating E. coli O157:H7, there was a need to further investigate this possibility under more rigorously controlled experimental conditions.
A study was carried out recently at the Agriculture and Agri-Food Canada Research Centre in Lethbridge to explore this seaweed extract under more challenging conditions. Each of the cattle in the experiment received an oral dose of almost 100 billion cells of E. coli O157:H7, which is 10,000× higher than what an animal would likely ever encounter in a natural feedlot environment. A mixture of four strains of E. coli O157:H7 was used to ensure that if the Tasco was effective, it would work against more than just one type of E. coli O157:H7. The 32 cattle used in the experiment were assigned to four treatment groups of 8 animals each. One of the groups was fed no Tasco, and was designated as the control group. A second group received Tasco in the diet at a concentration of 2% of dietary dry matter for 14 days while a third group received Tasco for the same period, but at only 1% of dietary dry matter. The fourth group received Tasco at a concentration of 2% of dietary dry matter for a 7-day period. The cattle were fed a grain-based finishing diet typical of those commercial feedlot industry. The 7- and 14-day treatment periods were selected with the intention that if the treatment was successful, the risk of E. coli O157:H7 entering the abattoir could be reduced by administering Tasco to cattle for a short period just prior to slaughter.
After inoculation of the cattle with E. coli O157:H7, fecal samples, oral swabs and samples from the feedlot environment were collected from each animal and pen over a 93 day period and assessed for E. coli O157:H7. Molecular techniques were used to identify which of the four strains were present in collected samples, and to confirm that the strains isolated were in fact E. coli O157:H7.
Including Tasco in the diet at 1%for 14 days or at 2% for 7 days reduced fecal shedding of E. coli O157:H7 by 10 to 100X as compared to feeding no Tasco. The most sensitive techniques were required to detect E. coli O157:H7 from day 66 onward in the control group (no Tasco), but in all of the cattle that were fed Tasco, fecal populations were low enough to require these same techniques from day 52 onward. Approximately 80% of the samples collected from control cattle were positive for E. coli O157:H7, compared with ~60% from the cattle fed Tasco. These results clearly indicated that Tasco could reduce shedding of E. coli O157:H7 even under the severe conditions of direct oral challenge with the bacterium. On-farm detection of this pathogen would have been impossible without these sophisticated molecular and microbiological techniques, however, because even with the extreme dose of E. coli O157:H7 given, none of the animals in the experiments exhibited any signs of sickness.
In this study, E. coli O157:H7 was also confirmed in 1 out of 56 water samples, 2 of 56 feed samples, and 32 of 56 fecal samples collected from the pen floor. These results suggest that fecal material on the pen floor is likely the primary method by which E. coli O157:H7 is transferred among cattle in the feedlot. Water and feed are likely more secondary sources of infection, thus steps taken to kill E. coli O157:H7 at these point sources will not likely result in a major reduction in the incidence of infection unless steps are also taken to reduce its presence in the feces.
The molecular techniques employed in this study confirmed that all four strains of E. coli O157:H7 used in the oral inoculum were represented among the isolates from fecal samples collected late in the sampling period, when shedding levels were low. This suggests that the effect of Tasco was not specific to one type of E. coli O157:H7. Rather, it had an impact on this group of bacteria as a whole. Tasco did not decrease generic E. coli in the digestive tract, thus there was no indication that "good E. coli" are adversely influenced by supplementation. Not all of the inoculated strains of E. coli O157:H7 were isolated from the environment, which suggests that the strains may differ in their ability to survive once they leave the digestive tract. A strain more adept at survival in the feedlot environment may be more likely to infect newly-arriving cattle.
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