The use of antibiotics in food animals selects for bacteria resistant to antibiotics used in humans, and these might spread via the food to humans and cause human infection, hence the banning of growth-promoters. The actual danger seems small, and there might be disadvantages to human and to animal health. The low dosages used for growth promotion are an unquantified hazard. Although some antibiotics are used both in animals and humans, most of the resistance problem in humans has arisen from human use. Resistance can be selected in food animals, and resistant bacteria can contaminate animal-derived food, but adequate cooking destroys them. How often they colonize the human gut, and transfer resistance genes is not known. In zoonotic salmonellosis, resistance may arise in animals or humans, but human cross-infection is common. The case of campylobacter infection is less clear. The normal human faecal flora can contain resistant enterococci, but indistinguishable strains in animals and man are uncommon, possibly because most animal enterococci do not establish themselves in the human intestine. There is no correlation between the carriage of resistant enterococci of possible animal origin and human infection with resistant strains. Commensal Escherichia coli also exhibits host-animal preferences. Anti-Gram-positive growth promoters would be expected to have little effect on most Gram-negative organisms. Even if resistant pathogens do reach man, the clinical consequences of resistance may be small. The application of the 'precautionary principle' is a non-scientific approach that assumes that risk assessments will be carried out.

/pdf/does-the-use-of-antibiotics-in-food-animals-pose-a-risk-to-8dlw905bby.pdf

Does the use of antibiotics in food animals pose a risk to human health? A critical review of published data

https://www.ars.usda.gov/alternativestoantibiotics/PDF/publications/11CastanonJIR.pdf

History of the Use of Antibiotic as Growth Promoters in European Poultry Feeds

During the past 10 years, multidrug-resistant Gram-negative Enterobacteriaceae have become a substantial challenge to infection control. It has been suggested by clinicians that the effectiveness of antibiotics is in such rapid decline that, depending on the pathogen concerned, their future utility can be measured in decades or even years. Unless the rise in antibiotic resistance can be reversed, we can expect to see a substantial rise in incurable infection and fatality in both developed and developing regions. Antibiotic resistance develops through complex interactions, with resistance arising by de-novo mutation under clinical antibiotic selection or frequently by acquisition of mobile genes that have evolved over time in bacteria in the environment. The reservoir of resistance genes in the environment is due to a mix of naturally occurring resistance and those present in animal and human waste and the selective effects of pollutants, which can co-select for mobile genetic elements carrying multiple resistant genes. Less attention has been given to how anthropogenic activity might be causing evolution of antibiotic resistance in the environment. Although the economics of the pharmaceutical industry continue to restrict investment in novel biomedical responses, action must be taken to avoid the conjunction of factors that promote evolution and spread of antibiotic resistance.

https://www.thelancet.com/pdfs/journals/laninf/PIIS1473-3099(12)70317-1.pdf

The role of the natural environment in the emergence of antibiotic resistance in Gram-negative bacteria

Microbes have made a phenomenal contribution to the health and well-being of people throughout the world. In addition to producing many primary metabolites, such as amino acids, vitamins and nucleotides, they are capable of making secondary metabolites, which constitute half of the pharmaceuticals on the market today and provide agriculture with many essential products. This review centers on these beneficial secondary metabolites, the discovery of which goes back 80 years to the time when penicillin was discovered by Alexander Fleming.

/pdf/microbial-drug-discovery-80-years-of-progress-2u89dilx0f.pdf

Microbial drug discovery: 80 years of progress

Probiotics and prebiotics in animal feeding for safe food production

Following the ban of all food animal growth-promoting antibiotics by Sweden in 1986, the European Union banned avoparcin in 1997 and bacitracin, spiramycin, tylosin and virginiamycin in 1999. Three years later, the only attributable effect in humans has been a diminution in acquired resistance in enterococci isolated from human faecal carriers. There has been an increase in human infection from vancomycin-resistant enterococci in Europe, probably related to the increased in usage of vancomycin for the treatment of methicillin-resistant staphylococci. The ban of growth promoters has, however, revealed that these agents had important prophylactic activity and their withdrawal is now associated with a deterioration in animal health, including increased diarrhoea, weight loss and mortality due to Escherichia coli and Lawsonia intra- cellularis in early post-weaning pigs, and clostridial necrotic enteritis in broilers. A directly attributable effect of these infections is the increase in usage of therapeutic antibiotics in food animals, including that of tetracycline, aminoglycosides, trimethoprim/sulphonamide, macrolides and lincosamides, all of which are of direct importance in human medicine. The theoretical and political benefit of the widespread ban of growth promoters needs to be more carefully weighed against the increasingly apparent adverse conse- quences.

/pdf/the-european-ban-on-growth-promoting-antibiotics-and-1or41u9os5.pdf

The European ban on growth-promoting antibiotics and emerging consequences for human and animal health

ABSTRACT Commercial chicken production for the supply of meat and eggs has expanded in the scale and variety of production systems in use to facilitate the supply of a range of cost-effective products in response to consumer demand. In the egg sector, traditional cage systems were required to be replaced in the EU by 2012, and most of this production capacity has been replaced by colony cage systems, which provide more space, perching, and environmental enrichment. In some countries there is significant production of “cage-free” or “barn” eggs in which the birds remain housed, but have access to litter. In the UK most egg production is now free-range. Meat poultry is produced in “barn” systems with various enrichments and some free-range. The rise in free-range production has seen the return of some diseases. Biosecurity is a critical tool for disease control in all production systems, particularly when disease challenge is high or farms are in a high poultry density area. An infectious dose of a pathogen is important in determining outcomes in terms of health and productivity, so biosecurity, hygiene, and good management are important across many diseases. Infections which are notifiable, of zoonotic importance and those which are sporadic or endemic in commercial poultry production are reviewed. General principles of preventative medicine applicable to the control of infectious diseases in different poultry production systems are proposed in areas such as biosecurity, system design and maintenance, range, and vaccination, though good management is always important.

Paul McMullin

Papers

The European ban on growth-promoting antibiotics and emerging consequences for human and animal health

Infectious diseases in free-range compared to conventional poultry production