Resistance Genes in the Food Supply

Your humble reported has been interested in nutrition since he was knee high to a puppy, and he has also been worried about the consequences of pesticides and other artificial chemicals getting into the food chain. He has also been worried about feeding all kinds of artificial potions to animals. Surely they would eventually turn up in humans, and we have little idea about all the things that they may do. It is also a worry that antibiotic resistance in humans could be passed on to bacteria in animals.

Some of these fears were born out at a conference – the 107th General Meeting of the American Society for Microbiology (ASM) – in Toronto this week.

A paper presented by Hua Wang of the Ohio State University suggests that the administration of antibiotics to animals could be contributing to the continuing rise of antibiotic-resistant infections in humans

The problem is a process known as horizontal gene transfer, in which bacteria that are in close proximity to each other can share genetic information, including genes that code for antibiotic resistance. Horizontal gene transfer between disease-causing bacteria has been known for years as an important avenue for the exchange of antibiotic-resistance genes among bacteria in hospitals. We all carry bacteria on and in our bodies. Some are beneficial, and help in things like digestion. Others are simply “passengers,” and we call these “commensal” bacteria.

Research has also already demonstrated that pathogenic bacteria have the ability to engage in horizontal gene transfer with the otherwise harmless bacteria that we all carry in our bodies. What concerns us is that these normally benign commensal bacteria have an enormous and diverse gene pool. That increases the likelihood of gene transfer. Some commensal bacteria exchange genetic information extremely quickly. That was helpful to the bacteria during evolution, but may be producing a boatload of problems for us today.

Dr Hua said:

“We have demonstrated not only that organisms carrying such intrinsic mechanisms have the potential to become an important reservoir for antibiotic resistance genes but, more importantly, that these intermediate organisms can disseminate antibiotic resistance genes in subsequent events much more effectively than the parental donor strain.”

“Once we no longer limit ourselves to food borne pathogens and look at commensal bacteria, we will find that the magnitude of antibiotic-resistant bacterial contamination in the food chain is tremendous.”

In a study published last year, she and her colleagues tested a range of ready-to-eat food samples that they purchased from several grocery chain stores. They included seafood, meats, dairy, deli items and fresh produce. With the exception of processed cheese and yogurt, antibiotic-resistance gene-carrying bacteria were found in many food samples that they examined.

The problem is not just confined to the food supply. Recent studies have shown antibiotic resistance genes in bacteria in the digestive tract of young infants. Since these children were still being breast- or formula-fed and had not yet eaten solid food, they must have acquired these genes somewhere other than the food supply. This suggests that resistance genes from the environment had somehow got into the infants.

Antibiotic resistance is a huge and ever-growing problem. For years now, many of us have worried about the over-prescribing of antibiotics when they are not needed. For example viruses cause the vast majority of sore throats, and few viruses respond to antibiotics. Yet patients often feel cheated if they do not leave a doctor’s office clutching a prescription. The result has been increasing numbers of resistant bacteria. When you really need an antibiotic, it may no longer be effective. Now we have another mechanism by which our actions have caused a problem that could quite literally be the death of us.