Friday, March 12, 2010

What's In My Meat?

It’s getting harder and harder to be an informed grocery shopper today, particularly when it comes to buying meat. Between “free range,” “organic,” and “natural,” options, it’s hard to know what kind of lives our chickens lived before they became thighs and breasts, or what hidden ingredients might be in our hot dogs. But behind these often vague labels are specific regulations that are monitored by the U.S. Department of Agriculture’s Food and Safety Inspection Service. What the label says about your meat:

Organic: Animals have been fed organic feed and raised without antibiotics or growth hormones using other management methods to minimize disease. They must be allowed access to the outdoors, but the amount of access is not specified under regulations. Organic farms are inspected by government-approved officials. Products labeled “made with organic ingredients” must be at least 70% organic; those labeled “organic” must contain at least 95% organic ingredients.

Natural: Meat has been minimally processed (in a way that does not “fundamentally alter the raw product”) with no artificial (synthetically- produced) ingredients.

Free range: Animals must have open-air access for at least five minutes a day. Other factors such as the density of animals are not specified.

Grass-fed: After weaning, animals are fed only grass and other forage, are able to engage in natural grazing behaviors, and can continuously access to a pasture during the growing season. However, at other times they may be confined and fed grass indoors. (See more on grass-fed beef in a recent New York Times blog post.)

Cage-free: Virtually all poultry raised for meat is “cage-free,” but egg-laying hens that are not cage-free are often kept in cages that greatly restrict movement. Cage-free animals do not have to have access to the outdoors.

Certified humane raised and handled: A non-governmental organization certifies farms that allow animals to engage in natural behaviors with sufficient space and that do not use antibiotics or hormones.

For the perpetually curious, the USDA also has a Meat and Poultry Hotline that accepts food-safety related questions.

Photo: Cage-free chickens
Image credit:

The Microbiology of Antibiotic Resistance, Part 1: Bacterial Cell Structure

“Last winter while being sickly and unable to taste, I examined the appearance of my tongue, which was very furred”.

- Anton van Leeuwenhoeck, 19 October 1674 Letter to the Royal Society, London. Royal Society. (Bardell D, Microbiological Reviews 1982)

From this examination of taste and tongue arose the first observation of “animalcules” by Anton van Leeuwenhoeck in 1674, which not only unraveled the mystery behind tongue furriness but also opened up a whole new world of life, invisible to the naked eye. Van Leeuwenhoeck’s discovery, eventually renamed bacterium by Christian Gottfried Ehrenberg in 1838, was revealed to be single-celled, prokaryotic (no membrane-bound organelles) microorganisms.

Improvements in visualization techniques have allowed scientists to study the structure of bacteria, which usually range from 0.5 – 5.0 micrometers in length and can come in a variety of shapes, from spheres to cylinders, spirals and rods.

At the most basic level, bacterial cells are encased by a cell envelope, which includes the most interior plasma (or cytoplasmic) membrane, the cell wall and, in some species of bacteria, an outer membrane. The cell wall filters, protects from internal pressure, and acts as an important classification characteristic based upon wall thickness and composition.

Gram-positive bacteria (which become purple when stained with Crystal Violet) possess a thick cell wall containing many layers of peptidoglycan, while Gram-negative bacteria (which retain no color when stained with Crystal Violet) have a double cell wall, containing only a few layers of peptidoglycan surrounded by an outer wall of carbohydrates, proteins and lipids.

Some bacteria have long, tail-like structure(s), projecting from the cell wall to the outside environment, called flagella. Through rotation, flagella provide a means of locomotion for bacteria. Short, hair-like projections called pili, usually covering the entire bacterial surface in high numbers, assist the bacteria in attaching to other cells or surfaces.

With no membrane-bound organelles (the equivalent of human organs), bacterial DNA, usually a singular, circular chromosome, is located in the nucleoid region of the bacterium’s inner gel-like matrix, cytoplasm. From DNA, ribosomes assemble amino acid chains, which eventually reorganize into functional proteins. Some bacteria also contain plasmids or extra DNA scattered throughout the cytoplasm that are not involved in reproduction.

Thursday, March 11, 2010

In the News: Antibiotics and Farm Animals

Is the use of antibiotics in farm animals contributing to resistance in humans? That depends on who you ask, but increasing evidence seems to be pointing towards a connection. The long-term, low-dose courses of antibiotics used in almost all farm animals in the United States create an ideal environment for the selection of resistant bacteria, which studies show can be passed to humans through food consumption and direct animal contact. After a ban on all antibiotic growth promoters was implemented in the European Union four years ago, U.S. regulators still waver on their policy stance - with much pressure from the food production industry to leave drug choices up to the farmers themselves.

The issue has been getting increased coverage in news outlets recently. Last month, Katie Couric reported on the link between antibiotic use in animals and human health and on the ban of antibiotic growth promoters in Denmark, the first of the EU nations to institute strict regulations on non-therapeutic drug use in animals. Couric quotes Stephen McDonnell, CEO of Applegate Farms, on the necessity of tighter restrictions on American food producers:

"We use too many antibiotics, we use too many growth promotants. The singular focus is to create cheap meat. That's not always the best thing for the health of the Americans who buy it. We think with some subtle changes - giving [farm animals] more space, feeding them a good diet, and not stressing them out by growing them too quicky - you don't even need to use antibiotics."

Response to Couric's reports was swift. H. Scott Hurd, Director of the WHO Collaborating Center for Risk Assessment and Hazard Identification in Foods of Animal Origin, picked apart her evidence with arguments against a ban on growth promoters. These opposing positions represent the back-and-forth that is behind a bill in the U.S. Congress, PAMTA, which would ban antibiotics as growth promoters. But both sides often suffer from the same lack of evidence: while antibiotic use and resistance surveillance is common in Europe, the U.S. does not monitor the amount of antibiotics fed to farm animals.

In the last week, national columnists have also chimed in on the issue. Nicholas Kristof of The New York Times recounted the story of a California executive stricken with antibiotic-resistant Escherichia coli and attributed increasing resistance to antibiotic use on factory farms, as well as overprescribing by doctors. Yesterday, veterinarian Patty Khuly published an op-ed in USA Today supporting a ban and justifying potentially negative economic and animal health consequences. Like many other experts, she sees overuse of antibiotics in food animal production as part of a larger problem:

"After all, antibiotic use in animal agriculture makes sense primarily because of how we crowd and transport creatures. Remove the antibiotics, and more animals will surely get sick in the short term. But long-term, that only means the industry will be forced to reform how it houses and ships its 'widgets.'"

Antibiotic Resistance 101

Antibiotic resistance is an inevitable result of the use of antibiotics, and is not a new concept. Even in the 1940’s, when penicillin was first mass-produced, resistant bacteria were recognized. But misuse and overuse of antibiotics both create added pressure for the development and spread of resistant bacteria, resulting in reservoirs of resistance that threaten treatment success in all regions of the world.

Acquired antibiotic resistance is the result of a genetic mutation that changes the way a microbe responds to a drug made to eradicate it. These responses vary greatly – for example, some genetically resistant bacteria have altered binding sites so that prevent antibiotic molecules from attaching to cell walls, others have mechanisms to pump out antibiotics when they do get inside.

Even before an antibiotic is administered, a portion of a bacterial population may be genetically resistant to that antibiotic. But adding a drug to the mix puts selective pressure on the community, killing those bacteria that are susceptible but allowing resistant bacteria to survive and multiply. This is especially a risk when antibiotics are administered at low doses not strong enough to wipe out whole populations, or when antibiotic therapy is initiated but then terminated before it can run its full course of wiping out an infection. This leaves lingering populations of bacteria that have been exposed to the drug and given the opportunity to develop resistance. Without susceptible bacteria to compete with, antibiotic-resistant bacteria can quickly multiply and develop into an infection that is no longer treatable by the usual drugs, requiring more aggressive treatment or sometimes leaving doctors with no options – especially in developing nations, where drug access is often limited.

Genes conferring antibiotic resistance can also propagate in commensal (non-disease causing) bacteria, which are native to all humans, and then be transferred to pathogenic bacteria through conjugation. Both commensal and pathogenic resistant bacteria can be spread through the food supply (e.g. Escherichia coli), or between humans in clincal or community settings (e.g. methicillin-resistant Staphylococcus aureus, or MRSA). These resistant strains are an increasing medical and economic concern - MRSA alone kills 19,000 Americans every year, and one recent study found that antibiotic-resistant infections cost the U.S. healthcare system more than $20 billion annually. The CDC and WHO both rank antibiotic resistance as one of the top three public health concerns worldwide.

Wednesday, March 10, 2010

Increasing Resistance in Soil Microbes in The Netherlands

Despite improved waste management practices and bans on antibiotic growth promoters, DNA isolated from soil microbes in the Netherlands shows that antibiotic resistant genes (ARGs) have become progressively more common in the past 70 years. A recent study by Danish and English scientists, published in Environmental Science and Technology, examined 18 different ARGs in five long-term soil series from different rural areas in The Netherlands, collectively spanning 1940-2008. After normalizing the ARG levels to cover a common time period for all of the series, 78 percent of the ARGs showed an increasing trend over time. Four out of the five sites displayed consistently increasing ARG levels. These increases were most pronounced for resistance to tetracyclines, but were also present for the three other classes of antibiotics examined: extended spectrum beta-lactamases, erythromycins, and glycopeptides. This figure shows these relative increase in genes encoding for resistance to three different antibiotics over the period studied.

These findings are signficant because antibiotic-resistant bacteria are capable of conferring resistance to other potentially disease-causing bacteria in the envrionment. Resistance in soil microbes could impact humans through food consumption or through the water supply and make human pathogens more dangerous and difficult to treat. It is also interesting that these increases in resistance occured in spite of improvements to waste management that were made in The Netherlands in the late 1970's, and bans on antibiotics as growth promoters in the European Union that were implemented between 1997 and 2006, suggesting that more efforts need to be made to both prevent and protect ourselves from environmental reservoirs of resistance.