Threat of Antibiotic Resistant Bacteria

Antibiotic Resistant Bacteria are on the Rise.

Anti-bacterial drugs, known as antibiotics, have saved countless lives by decreasing the severity of bacterial infections and reducing the health risk to humans. However, diverse bacterial species are continually mounting new defenses against anti-bacterial compounds, resulting in antibiotic resistance. Incidences of antibiotic resistant bacteria are now popping up throughout the world in staggering numbers. According to the CDC, last year the U.S. population experienced over 2 million illnesses due to antibiotic resistant bacteria. Of those reported illnesses, approximately 23,000 people died.

Since the 1940s, scientists have discovered and generated dozens of antibiotics to fight an array of bacterial species. Unfortunately, with the inception of almost every antibiotic drug, resistant bacteria arose in just a few years. Additionally, according to a CDC report, the discovery of new antibiotic drugs has diminished over the last three decades (Figure 1). These facts suggest new antibiotic drugs will not solve this problem (1).

Figure 1.

Pic1

With this post, I will explain why bacteria are gaining antibiotic resistance and detail the steps the United States government is enacting to end this problem – or at least slow it down.

Sources of Antibiotic Resistance

While most bacteria do not contain the genetic material to thwart antibiotic medication, one bacterium in an antibiotic laden environment may develop resistance that allows it to survive and replicate better than those lacking the necessary components that confer resistance. The surviving bacterium can then grow exponentially since it no longer needs to compete for resources. As a result, that one resistant bacterium can turn into millions of bacteria over night.

This is how antibiotic resistant traits gain dominance.

Furthermore, bacteria are able to confer antibiotic resistance to each other by sharing their resistance genes. These genes are normally found on small genetic elements called plasmids or transposons as well as bacterial viruses, known as bacteriophages, that can be transmitted to other bacteria. Resistance genes are best spread in environments containing a diverse array of microbes under the selective pressure of antibiotics. Hospitals are the obvious setting for this situation, and one of the main sources of antibiotic resistance (2). However, the biggest problem may reside in livestock antibiotic treatment (Figure 2).

Figure 2.

pic2

Livestock farmers use antibiotics to non-discriminately promote the health and growth of cattle, swine, poultry, and other animals in order to maximize profits. The country that utilizes the most antibiotics for livestock is China. A recent paper published in the journal PNAS asked the question: does China’s over use of antibiotics for livestock equate to higher levels of antibiotic resistant bacteria?

Most of the antibiotics fed to livestock are excreted in manure. Therefore, scientists from the Chinese Academy of Sciences tested the presence of antibiotic resistant genes in manure, soil, and compost samples from three different swine farms in China. They found manure samples contained the highest levels of antibiotic resistant genes. In a Beijing farm, these genes were detected at levels 121,000-fold higher than in control samples of manure from non-antibiotic treated swine. Soil and compost samples, which were derived from the manure, also contained a large amount of these genes. Shockingly, all of the major classes of antibiotics were detected which cover the common mechanisms for antibiotic resistance, including:

  • Efflux pumps: expel the antibiotic from the bacterium
  • Antibiotic deactivation: destroy the antibiotic drug
  • Cellular protection: block the cellular target of the antibiotic

Additionally, the scientists found the presence of many transposons in their samples, which directly correlated with the abundance of antibiotic resistant genes. Transposons mediate the movement of genes from one region of DNA to another. The presence of transposons in the collected samples suggests bacteria in manure utilize transposons to transfer antibiotic resistant genes to their neighboring bacteria (3).

If these data are correct, then residents of China should harbor large amounts of bacteria with antibiotic resistant genes due to environmental exposure. Indeed, a recent paper from the journal Nature Communications supported this hypothesis. Scientists from the Chinese Academy of Sciences analyzed the genomes of intestinal microbes from Chinese, Danish, and Spanish human populations. From this study, they found that Chinese individuals contained the highest diversity of antibiotic resistant intestinal bacteria (4).

These two publications support data from the existing scientific literature that focuses on one main point: antibiotic resistance is derived from the over use of antibiotic resistant drugs in the environment.

How do We Slow Down this Problem?

The CDC initiated four steps to limit the spread of antibiotic resistant bacteria (1):

  1. Promote healthy practices to diminish bacterial infections
  2. Monitor the presence and spread of antibiotic resistant bacteria
  3. Educate doctors and farmers on safer antibiotic usage
  4. Encourage the discovery of new antibiotic drugs

Additionally, the National Institute of Allergy and Infection Diseases (NIAID) recently published a report outlining their initiatives to combat antibiotic resistance through a multifaceted strategy of drug discovery and preventive action (5).

I believe education and drug restrictions, especially in regards to livestock treatment, are essential to easing this crisis. While many European countries have strict laws to reduce antibiotic usage for livestock rearing, the United States does not. Change may be on the horizon though. Late last year, the Food and Drug Administration (FDA) began an initiative for drug companies to voluntarily stop labeling and dispensing antibiotics for animal growth purposes and also recommended farmers treat livestock under the guidance of a veterinarian (6). The obvious weaknesses of this initiative are that it is voluntary, and the farmers may continue antibiotic usage by claiming that they are using the drugs for animal health purposes. Hopefully our government, and others around the world, will enact real reform before this crisis escalates beyond control.

Editor: Sharon Kuss

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