Critical Management Points Overview

Critical Management Points Overview

Transcript (with additional commentary)

In the 20th century, major strides were made in controlling once widely-feared scourges like tuberculosis, bacterial pneumonia, and post-surgical infections. With the development of antibiotic drugs, infections that once caused widespread disability or even death, were instead treatable, thereby improving quality of life for people and animals, while offering other advantages in agriculture.

Yet with all the benefits of antibiotics, their widespread use has resulted in increasing incidence of resistance–or the ability of some bacteria to survive, grow, and continue to cause infection in the presence of these drugs.

Antibiotic resistance is a serious human and animal health threat.  According to the U.S. Centers for Disease Control, approximately 2 million people in the United States become ill every year with resistant infections, and, of those who become ill, approximately 23,000 die. In 2006, the annual additional cost of treating hospital-acquired infections from just six species of antibiotic-resistant bacteria was estimated to be at least $1.87 billion – more than the annual spending on influenza.

In this video, learn how Virginia Tech is responding to better understand this public health challenge.

[Amy Pruden, Department of Civil and Environmental Engineering, Virginia Tech]: “My name is Amy Pruden and I’m a professor of civil and environmental engineering at Virginia Tech.  I’m the principal investigator on a U.S. Department of Agriculture grant that’s looking at critical control points for the spread of antibiotic resistance from manure to fresh produce.

“The big question we’re trying to answer is basically what’s in your vegetables. Right, it’s not a sterile environment.

“There are bacteria there, most times they’re not hurting us, who knows maybe they’re even beneficial, but sometimes there could be pathogens and there’s been a lot of work on how to keep our produce safe from pathogens like E. coli, but here we’re looking at it from a different angle, we’d like to know if antibiotic resistance could spread through vegetables that are eaten raw, like lettuce, broccoli, carrots, and radishes.”

Food animals, like beef cattle, dairy cattle, chickens, turkeys, and pigs, receive antibiotics just like people do. FDA-approved uses of antibiotics include: disease treatment for sick individual animals or animals in herds that are sick; Disease prevention for a group of healthy animals that are at risk of becoming sick; and Growth promotion or increased feed efficiency in a herd or flock of animals to promote weight gain.

However, antibiotics important for human health are recommended to be used in food animals only to treat disease and under the guidance of a veterinarian.

Plus, the United States has strict controls to prevent antibiotics from being in our meat or milk – For instance, the FDA mandates that each bulk tank of milk is tested for many antibiotics and if there’s even a trace, it can’t be sold. Carcasses in USDA-inspected slaughterhouses are also tested for antibiotics, through the Residue Detection Program.

So, how does this impact the development of antibiotic resistance?  Whenever antibiotics are used in humans or animals, antibiotic residues are excreted in feces and urine.  A residue is what remains in the body and is excreted after the majority of the drug has been metabolized (broken down). Also, any time antibiotics are used, there is the potential there may be bacteria present that are resistant to that antibiotic. These bacteria will survive and grow better than other bacteria in the presence of the antibiotic, or be “selected”.

Sometimes bacteria mutate and become resistant and sometimes they can share their ability to resist antibiotics with other bacteria.  Such mechanisms of bacterial evolution present a constant challenge both for developing new antibiotics and preventing the spread of resistance to existing antibiotics.

What happens to the antibiotics and the bacteria they target after they are excreted, enter wastewater, soil, and compost, and when that material is used to grow food crops?

This 3-year project aims to identify strategies for mitigating the spread of antibiotic resistant bacteria starting at the farm all the way to the fork, by looking at five critical control points along the way – 1) antibiotic use in food animals, 2) different manure composting methods, 3) amendment of manure or compost to different soil types, 4) different vegetables crops, and 5) post-harvest washing practices.

One highlight of this research is state-of-the-art laboratory methods, especially “metagenomics,” to look for bacterial genes that confer antibiotic resistance.

Antibiotic resistance genes in the environment pose special concern because they may be taken up and shared by active bacteria, which then have the ability to resist antibiotics.  Research is just starting to show how this method is involved in the spread of antibiotic resistance.

[Amy Pruden, Department of Civil and Environmental Engineering, Virginia Tech]: “This is very much a team effort and this research would not be possible without an environment like Virginia Tech, a land grant institute, where we have this mission of service, and an active Extension group where we’re working with the producer and grower community.”

Glossary of Terms

  • Antibiotic drugs – Compounds that kill or slow the growth of bacteria to treat or prevent infection.
  • Antibiotic residues – Antibiotic that remains in secondary material, either milk, meat, urine, or feces, after the antibiotic has been administered. Residues are generally not fully functional compounds, but are results of metabolism and other degradation processes.
  • Antibiotic resistance – Antibiotic resistance is the capability of some bacteria to survive antibiotic treatments. Some bacteria are intrinsically resistant, for example an antibiotic that specifically targets Gram positive bacteria will not affect Gram negative bacteria. However, bacteria can also acquire resistance, either through mutation or through sharing of antibiotic resistance genes, in which much higher doses of the antibiotic are needed to have the desired effect.
  • Antibiotic resistance genes – Pieces of DNA carried by bacteria that encode functions that allow bacteria to survive and grow in the presence of antibiotics.
  • Antibiotic resistant bacteria – Bacteria that are not controlled or killed by an antibiotic with a spectrum that includes that type of bacteria.  An antibiotic spectrum is the range of bacteria susceptible to that drug. (CDC, Antibiotic Resistance,
  • State of the art laboratory methods – Emerging processes used in research to learn more information about how our world works. Some examples include DNA extraction, a laboratory method for isolating DNA from a sample of animal, plant, bacteria, or virus of interest, and metagenomics analysis, which is a new laboratory research technique aimed at sequencing all of the DNA present in a sample. Metagenomics can be used to compare kinds of antibiotic resistance genes present in a sample, as well as the types of bacteria and other functional capabilities.


  • Aminov, R. 2010. A Brief History of the Antibiotic Era: Lessons Learned and Challenges for the Future. Frontiers in Microbiology. Vol 1. pp 1-7.
  • Beef Quality Assurance program (
  • 2006. Resistance to Anti-Infective Drugs and the Threat to Public Health. Cell. p 124.
  • Weiner LM, Fridkin SK, Aponte-Torres Z, et al. 2014. Vital Signs: Preventing Antibiotic-Resistant Infections in Hospitals — United States. MMWR Morb Mortal Wkly Rep 2016. 65:235–241. DOI: