By Tony Greaves
Several strategies can be used
By Tony Greaves
Several strategies can be used to protect against colonization by entero-pathogens
Dr. David J. Nisbet of the USDA, a Canadian and a lead researcher at the Southern Plains Agricultural Research Center in Texas, gave a presentation entitled “Novel Strategies for Pathogen Intervention in the G.I. Tract of Poultry” at the 2005 Poultry Service Industry Workshop.
Nisbet put forth the question, “Why should we intervene pre-harvest if processing plants ship a very clean product out of their doors?” His answer: “Anytime we can reduce the pathogen load on the incoming bird, it can only help.”
“Think about Walkerton – the rural and urban interface is blurring, environmental issues are impacting the general population,” he said. He also pointed out that people touch animals (at agricultural fairs, for instance) then get sick and blame farmers.
“Our biggest bang for the buck may be in pre-harvest intervention,” Nisbet stated, adding, “Some human pathogens don't cause disease in birds and shedding from infected birds may be at very low levels or even sporadic. Our detection of these pathogens is imperfect.”
However, Nisbet pointed out that some companies, generally larger ones, are now saying that they won't accept certain products, such as animals that have been fed antibiotics.
In 1994, a report estimated that contaminated food products caused 9,000 deaths per year. A 2002 survey found that 66 per cent of the confirmed food-borne diseases in the U.S. were caused by Campylobacter (5,006 cases) and Salmonella (6,028 cases).
“Therefore,” Nisbet pointed out, “control of food-borne pathogens continues to receive media attention and to influence government research. Initiation of HACCP has rnewed industry interest in food-borne pathogen control.”
He said that an additional impetus to the development of non-antibiotic intervention strategies is the current focus on reducing the use of antimicrobials in food producing animals.
Nisbet reported that the gastro-intestinal tract (GI tract) contains over 2,000 species and a trillion organisms, some beneficial, some pathogenic. Since they are all competing for nutrients, space and intestinal attachment sites, less competitive bacteria are eliminated. “So the overall goal of an intervention strategy is to create a gut environment that is beneficial for normal gut flora and detrimental to enteric pathogens.”
Dr. Nisbet reported that feeding birds lactic acid had the most effect on crop contents, but little effect in the hind gut.
He said that feed withdrawal prior to transportation clears the GI tract, thereby reducing the incidence of carcass contamination by gut contents. However, feed withdrawal has also been shown to increase crop pH and the number of Salmonella and Campylobacter contaminated crops. “Studies suggest that crop contamination during pre-slaughter feed withdrawal represents a significant critical control point for reducing the introduction of these two pathogens into the processing plant,” Nisbet stated.
Re-acidifying the crop with organic acids, such as lactic acid, has resulted in crop contamination by Salmonella being decreased from 46 per cent to four per cent in an on-farm test. Nisbet added, “Importantly, isolation of Salmonella in pre-chill carcass rinses was almost reduced 10-fold. But Campylobacter isolation was only reduced 25 per cent by this pre-harvest lactic acid treatment. This suggests that incorporation of some organic acids into the drinking water during feed withdrawal can reduce Salmonella contamination of crops and broiler carcasses during processing.”
In France, sodium chlorate is incorporated into toothpastes and has been used in low concentrations in veterinary and human medicine, said Nisbet. His lab recently investigated the use of a cost-efficient chlorate ion that is metabolized within specific bacteria to produce, intercellularly, a chlorite ion that is toxic to the individual cell.
Both Salmonella and E. coli O157:H7 are members of a very pathogenic family of organisms that show nitrate reductase activity, which co-metabolizes chlorate to chlorite, and is cytotoxic to the bacterium.
Studies with cattle rumens indicate that chlorate significantly reduced E. coli O157:H7 populations, but didn't alter total anaerobic bacterial counts. “Similarly,” Nisbet reported, “orally administered sodium chlorate significantly reduced cecal concentrations of Salmonella and E. coli in swine, but not potentially beneficial microbes.”
Nisbet said that as poultry have access to water during the feed withdrawal period, administering chlorate in the water could have an impact on the pathogen load that will be transported to the processing plant and reduce pathogen contamination in the final product.
Statistically, tests on broilers reduced Salmonella in the crop, however further investigation is required to maximize effectiveness in a commercial setting.
Because studies in Nisbet's lab suggest that carbohydrates, such as mannose and lactose, interfere with the adherence of bacteria to epithelial cells, Nisbet suggested that specific carbohydrates may be used to control Salmonella in day-old chicks.
Lactose in the water at 2.5 per cent or in the feed at 5 or 10 per cent significantly reduced Salmonella in the chick. In addition, lactose-treated chicks had significant increases in the levels of bacteriostatic acetic and propionic acids and decreases in cecal pH. Even more recent research has demonstrated that lactose significantly reduces Clostridium perfringens populations and the incidence of necrotic enteritis.
The concept within competitive exclusion is to establish a population of “good” bugs in the gut early in life, which initiates direct competition to pathogens and for attachment sites in the gut. Dr. Nisbet then showed electron micrograph slides. Untreated chicks showed no gut colonization, whereas in those treated with Preempt, a commercial competitive exclusion product, crypts in the gut wall were easily seen to be colonized by beneficial bacteria.
Nisbet reported that even at 21 and 43 days, these treated chicks had lower levels of Salmonella colonization. He added that this strategy works with many species of Salmonella and E. coli. He reported that it was somewhat effective with Clostridium perfringens, but had limited usefulness with Campylobacter jejuni.
Regarding commercial competitive exclusion cultures, Nisbet said that only “defined” cultures have been approved for use in the U.S. Undefined cultures have been widely used in much of the world, but not in the U.S. He added that neither industry demand nor the cost of the approved competitive exclusion products were able to sustain economic production.
He went on to recount how the introduction of alfalfa into the feed during the molt of layers reduced colonization with Salmonella enteritidis – if it is used in conjunction with chlorate.
Dr. Nisbet reminded service industry personnel that increased pressure on agriculture to decrease the use of antimicrobials in food animal production has driven the industry to look at alternative methods of maintaining the health of the gastro-intestinal tract in poultry. This goal is critical to supplying a more biologically safe poultry product.
He stressed that the above strategies represent only a few of the interventions that are available. Nisbet said, “New strategies are constantly being developed and evaluated, however, it is unlikely that any one strategy will adequately protect against GI tract colonization by entero-pathogens of high human consequence. Various strategies will need to be incorporated in a multiple hurdle approach to ensure gut health and food safety.”