Part II: Antibiotic resistance from farm to fork
When we catch a bug, we visit a doctor and get a dose of something to cure us of it; so why not just blast Salmonella with a dose of antibiotics and let that be the end of it? Simple question: not such a simple answer.
Since they were first discovered in the 1940´s, antibiotics have become the standard solution. The doctor prescribes them, the vet prescribes them and for the past 50 years or so they have been used to prevent diseases in farm animals from causing economic damage: while farm animals can recover from bacterial diseases, their reduced productivity makes it more viable to prevent disease instead of treat it. Many antibiotics, when used at sub-therapeutic doses (much lower than the dose needed to treat disease), have also been found to improve the growth of livestock: they turn feed into meat, milk, or eggs much more cost-effectively.
However, almost as soon as the growth-promoting properties of antibiotics in farm animals had become standard practice, reports began to appear in the scientific literature that showed that the bacteria were becoming immune to the drugs. There are a number of ways in which bacteria can develop immunity, but in the case of prophylactic antibiotics, it may be a case of "what doesn´t kill you makes you stronger" When an antibiotic is used at a low dose, it might actually help make that bug immune. This resistant strain will go on and multiply to produce a whole population capable of infecting anything they come into contact with - it becomes more prevalent in the population - a lesson which Germany has recently learned to its cost during the recent enterohemorrhagic E. coli outbreak (3250 people infected; 49 deaths so far). Using antibiotics has just increased the "selection pressure" in a natural process of bacterial evolution, by exposing them to agents that they then develop resistance to. The more we use antibiotics in animal and human health, the more chance there is of the bacteria developing resistance.
Alarming news emerged recently in a report from the Federal Institute for Risk Assessment in the European Union. Taking all strains of Salmonella into account, 60% of them are already multi-drug resistant:
"''''The proportion of Salmonella and E. coli isolates resistant to ampicillin, sulfonamides and tetracycline varied between 5 and 68 % in poultry, pigs and cattle. Some Member States reported a high occurrence of fluoroquinolone resistance in Salmonella isolates from poultry (5-38%)."
This is one of the regions in the world with the most stringent Salmonella surveillance and control systems. This can happen everywhere!
It has become clear that we have been arming our enemies for decades. Multiple resistance is now a big problem. If antibiotic resistance is transmitted to more common food-borne pathogens like Salmonella and Campylobacter, resistance could become a major problem, especially in vulnerable groups of people. When a patient develops a disease caused by one of these resistant bugs, the first antibiotic used against it might not be the one that works, giving the bacteria time to cause more damage.
Salmonella control in the food chain is an essential part of preventing illness and reducing the risk of developing antibiotic-resistant pathogens. Many countries have already banned the non-therapeutic use of antibiotics in livestock, including broilers and laying hens. For such control systems to be effective, every step of the food chain, from feed raw materials to home preparation has to be scrutinised. Integrated food chain surveillance systems for Salmonella are already in force in many countries.
In the poultry production chain, for example (both layers and broilers), there are many points in which intervention may be successful. All inputs into poultry production (including vermin, water, feed, visitors and new stock) need to be protected. Next to hygiene and management interventions, the control of Salmonella via dietary means has become very popular. Beginning decades ago with the use of antibiotics, which used to serve this purpose, but whose use is in decline due to emerging resistance, alternative dietary strategies have attracted much attention. It is well accepted that feed hygiene is successful in preventing accidental Salmonella contamination in the poultry house from developing into a food contamination problem. Naturally, feed producers are attracted by alternative feed-based control strategies.
To read Part I- Are you doing enough to control Salmonella? Click here