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As part of her research work, veterinary student Beverly Morrison analyzed samples of seafood taken from Canadian grocery stores and food markets. Photo: Beverly Morrison.

Searching for antibiotic resistance in food

To me, staring at bacteria in a petri dish is a wonderful sight.

Each type of bacteria has a different shape, colour, texture and even smell. Depending on what you are testing, sometimes it feels like playing a game of chance on what will or will not grow. In the end, nothing is more satisfying than opening the incubator door and finding bacterial growth.

However, not everyone shares the same enthusiasm for bacteria as I do – especially when looking for antibiotic resistance.

This past summer I spent my days working in a research lab at the Western College of Veterinary Medicine (WCVM), processing seafood samples that originated from a wide variety of Asian countries.

My goal: to see if any superbugs reside on these food items.

This research is part of a larger study that was initiated by my supervisor, Dr. Joe Rubin, an assistant professor in the WCVM's Department of Veterinary Microbiology. My project will add to the original pilot study by analyzing additional samples taken from grocery stores and food markets in Saskatoon and other cities across Canada.

The study's focus is on samples carrying gram-negative bacteria that produce enzymes called carbapenemases. These enzymes degrade carbapenems – a class of anti-bacterial drugs that possess a broad spectrum of activity with the greatest effectiveness against gram-negative bacteria in particular.

"Carbapenemases allow bacteria to be resistant to the most commonly used and last-line-of-defense drugs we have for treating resistant, hospital-acquired infections in people," says Rubin, who is collaborating with the Public Health Agency of Canada (PHAC) and Canadian Integrated Program for Antimicrobial Resistance Surveillance (CIPARS) for this project.

His initial study, which included a small number of seafood samples from Asian markets in Saskatoon, identified the first food-borne, carbapenemase-producing organism. This discovery, which has significant implications for food safety and public health, gained instant global media attention after his research was published in the international journal, Emerging Infectious Diseases.

Carbapenemase-producing bacteria aren't yet common in Canada, so when these infections are encountered domestically, it often indicates that patients have visited other areas of the world or have had contact with others who have travelled internationally.

Finding this organism in squid indicates that a much broader segment of the population is potentially at risk of exposure to these resistant bacteria, says Rubin.

As part of her research work, veterinary student Beverly Morrison analyzed samples of seafood taken from Canadian grocery stores and food markets. Photo: Beverly Morrison.

A major concern is that bacteria can share DNA with each other by a process called horizontal gene transfer. This allows DNA — including resistance genes — to be exchanged with other bacteria in the environment.

"Say I had blue eyes, and you had brown eyes, and I want to change my eye colour. If I was a bacteria, I could just take that DNA from you and change my physical appearance," says Rubin.

If a person eats a food item carrying this particular type of drug-resistant bacteria, the organism could potentially exchange DNA with potentially pathogenic bacteria in the individual's intestinal tract that could then cause an untreatable infection in the future.

The United States and Canada have active antimicrobial resistance surveillance programs — but they're limited in scope. The programs focus on beef, pork and poultry and target primarily disease-causing bacteria.

As populations in countries like Canada and the U.S. become more diverse, so do the food items that are being imported from overseas. Rubin says these imported meats may constitute an unrecognized source of antimicrobial-resistant organisms, including carbapenemase producers.

For concerned members of the public, Rubin stresses that it's important to practise good food hygiene. "Transmission can be prevented by making sure we don't cross-contaminate raw meat and ready-to-eat food."

He adds that people need to use different cutting boards for raw meat and other food products. They also need to wash their hands thoroughly, clean kitchen surfaces and cook food to a proper internal temperature— ensuring that any bacteria in the food are killed.

Back in the research lab where I have finished testing all of the samples, I'm surprised by just how different bacteria are from one another. For example, bacteria from the same seafood item had a different pattern of resistance to the antibiotics being tested.

Bacteria never cease to amaze me.

 

Beverly Morrison of Victoria, B.C., is a second-year veterinary student who was part of the WCVM's Undergraduate Summer Research and Leadership program in 2014. Beverly's story is part of a series of articles written by WCVM summer research students.
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