Organic foods, such as meat, poultry and dairy products, as well as produce, are distinguishable from their conventional counterparts with respect to antibiotic residues and the bacterial flora in, and on the foods.  There is mounting evidence that subtherapeutic doses of antibiotics, or more broadly, antimicrobials, given to animals in their feed is promoting the growth of multiple-resistant strains of bacteria. This is a potential threat to the health of animals and humans alike.

    One-half of the world’s production of antibiotics is for animal husbandry and 80% of this is added to feed in subtherapeutic doses to promote growth (1).  The mechanism of antibiotic growth promotion is not well understood, but this practice has allowed animals to thrive, even in stressful conditions such as overcrowded quarters.  In 1994, animals in Denmark received 24,000 Kg of avoparcin in their feed.  In comparison, only 24 Kg of vancomycin, a similar glycoprotein, was prescribed for human therapy (2).

     Antibiotics are also utilized in agriculture as an aerosol sprayed across fruit trees, for example.  At the time of spraying, all of the targeted bacteria will be killed.  However, the antibiotic residue that remains encourages the growth of resistant bacteria (2).  The resistant bacteria move along in the food chain and eventually enter the intestinal tract of humans.

    Consumption of low doses of antibiotics selects for resistant bacteria that may contaminate food (3).  The resistant bacteria move freely in the environment from the infected animals to their human caretakers.  Farm workers have been found to have high levels of resistant bacteria among their intestinal flora (1).  Consumers encounter resistant bacteria in meat that is undercooked, and in raw fruits and vegetables.  Even when produce is washed thoroughly, a number of bacteria remain attached.  Antibiotic-resistant enterococci and staphylocci from animals are found in raw cured sausages and raw milk cheeses when they survive the production process (4).  Resistant bacteria, such as the strains found in farm workers are usually harmless, and do not normally pose a health problem.  The problem arises when the genes for antibiotic resistance are conferred to pathogenic bacteria.

     Bacteria acquire resistant genes in several ways.  Resistance is “inherited” from previous cell division, or from a mutation that offers protection from an antibiotic’s mode of action.  Often, bacteria acquire resistance by taking up a resistance gene from other bacteria.  Resistance genes are carried on plasmids, circular double-stranded DNA that is independent of the chromosomal DNA, where resistance genes may also reside.   Bacteria have evolved a few mechanisms for sharing their resistance genes.  In conjugation, a special type of plasmid allows the direct transfer of DNA from one strain to the other.  In a process known as transduction, resistance genes are transferred by viruses.  After a virus docks with and attaches to the cell-wall of a bacterial cell, it injects its viral DNA/RNA into the host cell with its syringe-like core.  The viral DNA/RNA is eventually incorporated into the host genome and may confer antibiotic resistance if a gene conferring antibiotic resistance is present in the viral DNA/RNA nucleotide sequence.  A bacterial cell can even gain a resistance gene by taking up a gene fragment of a dead bacterial cell that has released its cell contents into the environment.

     Instances of pathogenic bacteria developing resistance to life-saving antibiotics are becoming more prevalent.  Fluoroquinolone use in the poultry industry has resulted in the emergence of a fluoroquinolone-resistant Campylobacter jejuni.  This resistant strain has been found in both meat products and infected human patients.  Prior to the use of fluoroquinolone in poultry husbandry, there is no record of resistant Campylobacter in humans that had no previous quinolone exposure (3).  In another case, direct evidence relating antibiotic use in animal husbandry to outbreaks of Salmonella infections in humans  was presented at a meeting of the Would Health Organization on October 20, 1997 (5).
     Antibiotics are self-defeating, in that their action promotes resistance.  When an antibiotic is introduced into a population of bacteria, those susceptible will be killed.  This void creates reduced competition for the resistant bacteria to proliferate.  It is apparent that subtherapeutic doses of antibiotics select for resistant bacteria.  The resistant bacteria move from the farm through the food chain, and take up residence in the intestinal tract of both animals and humans.  When resistant bacteria happen to confer their resistance genes to a strain of bacteria that are pathogenic, the treatment options for human patients may be gravely limited.  For this reason, “organic” farmers and meat and poultry producers refrain from using antibiotics as growth promoters.  Lack of antibiotic residue, and the resistant bacteria that are prone to colonize the animals maintained on a regiment of subtherapeutic antibiotics, distinguish the meat from cattle grown naturally from their conventional counterparts.  For an example of a company that strives to produce a wholesome product free of antibiotics and other additives, visit the web site of Laura’s Lean Beef (6).

(1) Facts About Antibiotic Use and the Impact on Resistance:
              Fact Sheet #4 “Antibiotics and the Resistance Gene Pool.”
           Antibiotic Resistance Factsheets

(2)  Witte, Wolfgang.  “Biomedicine: Medical Consequences of
             Antibiotic Use in "Agriculture”  Science – Witte 279 (5353):996
           Science -- Witte 279 (5353): 996

(3)  Perreten, Vincent.  “Antibiotic Resistance Spread in Food” Nature
             389, 801-802(1997)

(4)  Levy, S.   “The Challenge of Antibiotic Resistance.”   Scientific
            American March 1998
           http://www.sciam.com/1998/0398issue/0398levy.html

(5)  World Health Organization, Press Release  20 October 1997
              Antibiotic Use in Food-Producing Animals Must be Curtailed

(6) Laura's Lean Beef: Great tasting, lean, all natural beef!