E. coli remains one of the most frequently detected bacterial agents in swine samples tested at U.S. veterinary diagnostic laboratories. Understanding long-term trends in E. coli virulence gene detection is key to interpreting diagnostic results and guiding prevention strategies.
Here are five things you need to know about E. coli detection.
1. Not all E. coli are the same; virulence factors matter
Although E. coli is a normal inhabitant of the pig gut, only a subset of strains poses a health risk. The pathogenic potential of this bacterium depends on the presence and combination of specific virulence factors, including attachment genes (e.g., F18) and toxin genes (e.g., STb). The detection of virulence factors within a single isolate defines a virotype (e.g., F18:STb), which can then be classified into pathotypes (e.g., ETEC) based on disease mechanisms. Tracking these combinations is crucial for distinguishing harmless strains from those associated with clinical disease.
2. There is more beyond E. coli isolation
Once a sample arrives at the diagnostic laboratory, it is first processed for bacterial culture, which may result in the isolation of E. coli. While culture confirms bacterial growth and allows selection of representative colonies for antimicrobial assays, it does not consistently provide information on the pathogenic potential of the isolated E. coli. To address this, E. coli colonies may be subsequently tested by PCR genotyping for a panel of virulence genes. In recent years, over 30% of isolated E. coli have been characterized as not pathogenic, emphasizing the importance of PCR genotyping.