NOV 08, 2015 2:16 PM PST

How Listeria monocytogenes has Evolved to Persist in Foods and Cause Outbreaks

WRITTEN BY: Sarah Hertrich
L. monocytogenes is a bacteria that can be found anywhere in nature. It is a psychrotolerant pathogen, meaning, that it is able to survive and even grow at refrigeration temperatures. Outbreaks of listeriosis generally take place over a long period of time and are caused by refrigerated ready-to-eat foods such as milk, cheeses and deli meats. According to a recent report released by the Interagency Food Safety Analytics Collaboration (IFSAC) Project, L. monocytogenes is considered a high priority pathogen due to the frequency and severity of the illness it causes as well as its susceptibility to targeted interventions. It is estimated to be the cause of 94 % and 15.9 % of hospitalizations and mortalities, respectively, linked to foodborne illness.

L. monocytogenes isolates divide into four distinct phylogenetic lineages. Isolates in lineage I are responsible for the majority of foodborne outbreaks. Isolates in lineage II have been implicated in large epidemics and are the cause of sporadic cases of foodborne illness. Lineage III and IV isolates are rarely associated with disease in humans.
 
Scientists use multi-locus sequence typing (MLST) to study the evolution of L. monocytogenes and their ability to persist in non-host environments such as food processing plants.


Scientists from North Dakota State University used a molecular typing technique to investigate the genetic diversity of 124 L. monocytogenes isolates from various sources in order to determine if there was any correlation between the ability of isolates to cause disease and their genetic makeup. They focused on isolates from lineages I and II since they are most associated with disease in humans. Isolates were inoculated into a growth medium that was limited in nutrients to test the ability of each isolates to grow in an environment not ideal for growth, such as a food processing environment. They also used multi-locus sequence typing (MLST) to determine the genetic characterization of each isolate. 

The isolates had variable growth rates in the nutrient-limited medium however; scientists were unable to determine if there was a link between growth rate and a specific lineage or serotype. Isolates in lineage I had significantly lower growth rates compared to those in lineage II. Genetic characterization using (MLST) revealed that the 124 isolates represented 81 different sequence types and 33 different clonal complexes, indicating the diversity of the isolates used in this study. The authors were unable to make any correlations between serotype or source of the isolates (human, food, environment or animal) and growth rate. However; authors concluded that the ability if lineage II isolates to grow faster than lineage I in nutrient-limited medium may facilitate their ability to persist in non-host environments leading to a higher risk of food contamination and transmission of the pathogen through food to humans. This study also highlights the importance of molecular subtyping in evolutionary analysis in pathogens to facilitate surveillance, detection and control of pathogens.

Source: Foodborne Pathogens and Disease; IFSAC; Emerging Infectious Diseases; LabRoots; Genetic Diversity in Microorganisms
 
About the Author
  • I am a postdoctoral researcher with interests in pre-harvest microbial food safety, nonthermal food processing technologies, zoonotic pathogens, and plant-microbe interactions. My current research projects involve the optimization of novel food processing technologies to reduce the number of foodborne pathogens on fresh produce. I am a food geek!
You May Also Like
FEB 01, 2021
Cell & Molecular Biology
Dead Cells Can Teach Us About Life's Origins
FEB 01, 2021
Dead Cells Can Teach Us About Life's Origins
When an organism dies, it begins to decay. It's long been assumed that after death, the cells in an organism break down ...
FEB 02, 2021
Cell & Molecular Biology
Muscle Cells Can Block Inflammation When Exercised
FEB 02, 2021
Muscle Cells Can Block Inflammation When Exercised
Inflammation can be a crucial process; the body needs it to heal injuries and prevent infection. But inflammatory proces ...
FEB 16, 2021
Cell & Molecular Biology
A Change in One Gene Might've Made Our Brains Uniquely Human
FEB 16, 2021
A Change in One Gene Might've Made Our Brains Uniquely Human
Stem cells can be used to create simplified versions of human organs called organoids, enabling researchers to study how ...
MAR 19, 2021
Cell & Molecular Biology
These Cells Can Cry Tears
MAR 19, 2021
These Cells Can Cry Tears
Reporting in Cell Stem Cell, scientists have engineered miniature versions of human tear glands that actually emit tears ...
APR 04, 2021
Cell & Molecular Biology
Human Malaria Trial Creates More Questions
APR 04, 2021
Human Malaria Trial Creates More Questions
Malaria is a major health problem in many parts of the world; nearly half a million people die from malaria, and another ...
APR 08, 2021
Clinical & Molecular DX
Marijuana Versus Tobacco: Which Is Worse for Your Lungs?
APR 08, 2021
Marijuana Versus Tobacco: Which Is Worse for Your Lungs?
Canadian researchers have observed that individuals who smoke marijuana are more at risk than tobacco cigarette smokers ...
Loading Comments...