Multi-drug-resistant disease bacteria – which can shrug off all available antibiotics and be very difficult to treat – are a real, growing threat.
And causal antibiotic use on conventional livestock farms is proven to promote development of antibiotic-resistant bacteria that can spread to humans (Carlet J et al. 2011).
Nor is this use generally necessary, absent the seriously crowded, unhealthful conditions found on many factory farms.
In fact, antibiotics were first fed to chickens because they accelerate growth rates, for reasons still unclear.
Antibiotic feed additives also help prevent disease on crowded, factory-style chicken, duck, and turkey farms.
But it's the growth-spurring power of antibiotic feed additives that makes them standard on most poultry farms … especially farms owned or controlled by big agribusinesses.
Novel study examines effect of organic farming on resistant bugs
A new study, led by Dr. Amy Sapkota of the University of Maryland School of Public Health, found that poultry farms that have transitioned from conventional to organic practices and ceased using antibiotics have significantly lower levels of drug-resistant enterococci bacteria.
As she and colleagues wrote in an earlier paper, “current [conventional] animal feeding practices can result in the presence of bacteria, antibiotic-resistant bacteria, prions, arsenicals, and dioxins in feed and animal-based food products” (Sapkota AR et al. 2007).
Unfortunately, industrial fish farms can also contribute to the risk of drug-resistant bacteria, as her team noted in another study:
“…current aquaculture practices can lead to elevated levels of antibiotic residues, antibiotic-resistant bacteria, persistent organic pollutants, metals, parasites, and viruses in aquacultured finfish and shellfish” (Sapkota AR et al. 2008).
Her team's study is the first to demonstrate lower levels of drug-resistant bacteria on newly organic farms in the United States … and suggests that removing antibiotic use from large-scale U.S. poultry farms can result in immediate and significant reductions in antibiotic resistance for some bacteria.
“We initially hypothesized that we would see some differences in on-farm levels of antibiotic-resistant enterococci when poultry farms transitioned to organic practices. But we were surprised to see that the differences were so significant across several different classes of antibiotics even in the very first [organically produced] flock…” explained Sapkota. “It is very encouraging” (UM 2011).
Organic shift on poultry farms cuts drug resistant bugs sharply
Sapkota's group studied ten conventional and ten newly organic large-scale poultry houses in the mid-Atlantic region (Sapkota AR et al. 2011).
They tested for the presence of enterococci bacteria in poultry litter, feed, and water, and tested its resistance to 17 common antimicrobials.
They chose to study enterococci because these microorganisms are found in all poultry, including poultry on both organic and conventional farms.
Enterococci commonly afflict hospital patients, and many of the antibiotics added to farm animals' feed are active against Gram-positive bacteria such as the enterococci.
Therefore, as Sapkota explained, “These features, along with their reputation of easily exchanging resistance genes with other bacteria, make enterococci a good model for studying the impact of changes in antibiotic use on farms.” (UM 2011)
While all farms tested positive for the presence of enterococci in poultry litter, feed, and water as expected, the newly organic farms were characterized by a significantly lower prevalence of antibiotic-resistant enterococci.
For example, two-thirds (67 percent) of Enterococcus faecalis recovered from conventional poultry farms were resistant to erythromycin, while less than one-fifth (18 percent) of E. faecalis from newly organic poultry farms were resistant.
And dramatic drops in the levels of multi-drug resistant bacteria (organisms resistant to three or more antimicrobial classes) were also seen on the newly organic farms.
Forty-two percent of E. faecalis from conventional farms were multi-drug resistant, compared to only 10 percent from newly organic farms, and 84 percent of E faecium from conventional farms were multi-drug resistant compared to just 17 percent of those from newly organic farms.
Dr. Sapkota stressed a key point: “… at least in the case of enterococci, we begin to reverse resistance on farms even among the first group of animals that are grown without antibiotics” (UM 2011).
She expects that reductions in drug-resistant bacteria on US farms that go organic are likely to be more dramatic over time as reservoirs of resistant bacteria in the farm environment fade out.
Carlet J, Collignon P, Goldmann D, Goossens H, Gyssens IC, Harbarth S, Jarlier V, Levy SB, N'Doye B, Pittet D, Richtmann R, Seto WH, van der Meer JW, Voss A. Society's failure to protect a precious resource: antibiotics. Lancet. 2011 Jul 23;378(9788):369-71. Epub 2011 Apr 7
Mathew AG, Cissell R, Liamthong S. Antibiotic resistance in bacteria associated with food animals: a United States perspective of livestock production. Foodborne Pathog Dis. 2007 Summer;4(2):115-33. Review.
Sapkota A, Sapkota AR, Kucharski M, Burke J, McKenzie S, Walker P, Lawrence R. Aquaculture practices and potential human health risks: current knowledge and future priorities. Environ Int. 2008 Nov;34(8):1215-26. Epub 2008 Jun 18. Review.
Sapkota AR, Hulet RM, Zhang G, McDermott P, Kinney E, Schwab K, Joseph SW. Lower Prevalence of Antibiotic-resistant Enterococci On U.S. Conventional Poultry Farms That Transitioned to Organic Practices. Environ Health Perspect. 2011 Aug 10. [Epub ahead of print]
Sapkota AR, Lefferts LY, McKenzie S, Walker P. What do we feed to food-production animals? A review of animal feed ingredients and their potential impacts on human health. Environ Health Perspect. 2007 May;115(5):663-70. Epub 2007 Feb 8. Review.
University of Maryland (UM). Poultry farms that go organic have significantly fewer antibiotic-resistant bacteria. August 10, 2011. Accessed at http://www.eurekalert.org/pub_releases/2011-08/uom-pft080811.php