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OVC Researcher Studies Antibiotic-Resistant E. coli Bloodstream Infections

Escherichia coli, also known as E. coli (iStock_Credit_luismmolina)E. coli infections are becoming more common in humans, and research at the University of Guelph’s Ontario Veterinary College (OVC) has found that the risk to patients with E. coli bloodstream infections is rising.

Escherichia coli, also known as E. coli, is a common bacteria species spread by consuming contaminated food or drink, touching contaminated surfaces and contact with infected people or animals.

Most E. coli do not cause disease in healthy people and are an important part of our normal gut flora. However, some can give rise to illness. Once a person has contracted a disease-causing E. coli, the bacteria may spread to the bloodstream and cause bacteremia, also known as a bloodstream infection. E. coli is the most common cause of bloodstream infections in humans and can potentially lead to death in infected patients.

Dr. Melissa MacKinnon completed her PhD at OVC in 2021 in population medicine with a focus on epidemiology.  Dr. Melissa MacKinnon, who recently completed her PhD at OVC, warns that affected patients are more likely to encounter severe outcomes from E. coli bloodstream infections due to increasing antibiotic resistance - when bacteria become resistant to the medicines used to treat them. A three-time OVC alumna, MacKinnon completed her DVM in 2008 and an MSc in 2017, before completing her PhD in 2021 in population medicine with a focus on epidemiology.

As part of her PhD studies, MacKinnon found that infections by antibiotic-resistant E. coli resulted in significantly longer hospital stays and higher likelihood of patient death.

Under the supervision of Dr. Scott McEwen, a professor in OVC’s Department of Population Medicine, MacKinnon focused on E. coli that were resistant to third-generation cephalosporins - a group of antibiotics routinely used in patients with bloodstream infections, and to treat severe E. coli infections.

MacKinnon found that patients suffering from third-generation cephalosporin-resistant E. coli bloodstream infections were at greater risk of death within 30 days of infection. Her results also demonstrated that E. coli bloodstream infections carry a high mortality rate – mortality rate refers to the frequency of deaths in a population during a specified time.

MacKinnon says that her findings “highlight the increasing prevalence of E. coli bloodstream infections; we are seeing more of them, but also seeing more antibiotic resistance.”

Understanding and preventing antibiotic resistance in E. coli is critical in human medicine, as doctors are often forced to turn to last-resort antibiotics when third-generation cephalosporins are found to be ineffective. As these powerful antibiotics are used more often, E. coli bacteria can develop further resistance. When this happens, there could be no effective antibiotics available for a previously treatable infection.

“A lot of our current treatments and surgeries are possible thanks to antibiotics,” MacKinnon shares. When a patient is suffering from an infection requiring treatment, clinicians typically prescribe “first-line treatment” – the first-choice antibiotics that were historically effective and well tolerated. If this medication does not resolve the infection, clinicians prescribe second-line or third-line antibiotics that are reserved only for when these treatments fail. These stronger antibiotics will hopefully kill off the harmful bacteria to resolve the infection.

MacKinnon advises, “We can't keep relying on second- and third-line antibiotics, as bacterial resistance to these treatments is increasing and we don’t have many new antibiotics in development.”

In order to achieve this, MacKinnon hopes that all clinicians continue to recognize antimicrobial resistance as a threat and act to decrease antibiotic resistance by using antibiotics carefully.

She believes that E. coli infections deserve special attention - “They are common, increasing, and we need to determine appropriate interventions for decreasing them.”

MacKinnon’s PhD program was funded in part by a Frederick Banting and Charles Best Canada Graduate Scholarship from the Canadian Institutes of Health Research (CIHR) and a Brock Doctoral Scholarship from the University of Guelph. For her PhD projects, she collaborated with researchers from the Public Health Agency of Canada and the International Bacteremia Surveillance Collaborative.

Since completing her PhD, MacKinnon began a Post-Doctoral Fellowship at the University of Waterloo’s School of Public Health and Health Systems (SPHHS) with funding from CIHR. She is working with Dr. Shannon Majowicz, associate professor at SPHHS, to assess the associations between antimicrobial use and foodborne infections in residents of British Columbia.