Vive la résistance? (Antibiotics)

People who shy away from buying meat from animals given antibiotics do so to avoid exposure to antibiotic residues or to antibiotic resistant microbes. Modern germ warfare has significantly improved the quality and longevity of human life…as it has for animals, too…and the prospect of antibiotic resistance threatens that accomplishment.

Before we discuss the antibiotics that may have been used in producing your hamburger, we’ll stage the context: hands and dishes that contact it have just been washed with antibacterial soap, and the kitchen counters have been wiped down with antibacterial wipes. Maybe you nicked your finger cutting the tomato and applied Neosporin to it, and maybe it’s allergy season, so you’re fighting a sinus infection with the help of an antibiotic.

Funny how agriculture gets all the attention for an antibiotic scare…when one third of people try to take antibiotics for the common cold (McNulty et al., 2007), or when somewhere between 10 and 44% of people quit taking their antibiotics before the prescribed duration when they start feeling better (Pechere et al., 2007).

Antibiotics have a specific withdrawal date: they can only be administered before a certain time frame before the animal is harvested. Like synthetic hormones, antibiotic products are excreted from the body or decompose within the body. The “withdrawal date” denotes the time by which this elimination has been carried out to a satisfactorily low, safe level. Meat products are also routinely tested for antibiotic residues. If they test positive, they are thrown out and never enter the food supply. See these resources by beef.org: Antibiotic Use in Cattle and Antibiotic Approval Process.

In beef cattle production, antibiotics are used therapeutically (in response to serious illness) and subtherapeutically (pre-emptively or for improving efficiency). Subtherapeutic antibiotics like metaphylaxis, tylosin, and monensin are used to reduce sicknesses by 50% upon receiving a cattle shipment, to improve growth efficiency by 17% and reduce respiratory problems, and to improve feed efficiency by 10%, respectively (Wileman et al., 2009; Griffin, 2007)

Metaphylaxis can consist of the following drugs: Ceftiofur (Naxcel & Excenel), Florfenicol (Nuflor), long-acting Oxytetracycline, and Tilmicosin (Micotil) and chlortetracycline and sulfamethazine (Griffin, 2007)

In human medicine, these are either used ubiquitously (like tetracycline) or not at all. On its own initiative, the beef industry is emphasizing low stress shipping and handling of calves in working pens, sale barns, or trailers. Slow, reduced-stress weaning techniques also reduce the prevalence of shipping fever and respiratory diseases that are common to cattle that newly arrive to feedlots. The industry is en route to mandating best practices that would preclude the need for metaphylaxis treatment. The Beef Quality Assurance website has more information on self-regulation in the beef industry. After this treatment, unless a feedlot steer becomes sick (he’ll be quarantined and his file becomes red-flagged), no other antibiotic treatment other than tylosin and monensin or lasalocid will be administered.

Tylosin and monensin (or lasalosid, an ionophore like monensin) pose no threat to human medicinal effectiveness because these antibiotics are not used in human medicine. Also, the killing efficacy of ionophores is due to macro-mechanisms that are extremely unlikely to be overcome by bacterial gene mutations (Russell and Houlihan, 2003).

Monensin and lasalosid eliminate inefficient rumen microbes and promote efficient ones so that cattle can derive more energy from their food and waste less carbon-hydrogen molecules on methane production and eructation. Ionophore use reduces methane emissions in cattle and fosters efficient beef production: more gain on less feed…and we’re back to the “carpool effect.” I went into a grocery store last week and saw a note from the farmers that produced the meat which bragged, “We raised this beef without the use of ionophores!” I was disappointed.

What I finally find to be most interesting is that the same prevalence of resistant bacterial strains has been found on both organic, “antibiotic-free” animal production systems and conventional systems in large-scale studies of poultry, swine, and beef cattle operations (Young et al., 2009; Barlow et al., 2007). That tells me antibiotic resistance is far more likely to be linked to household abundance and prescription abuse than to agricultural practices. What do you Think?