Diversity of Mycoplasma hyopneumoniae strains from pigs across Ontario, Canada.

Mycoplasma hyopneumoniae causes highly contagious swine enzootic pneumonia worldwide. It has been reported that highly diversified M. hyopneumoniae strains exist in different parts of the world. We found p146 gene sequencing analysis, an affordable and simple-to-perform typing method, to be specific and highly sensitive when applied to the molecular typing of 113 M. hyopneumoniae-positive clinical samples directly without culture. The samples were submitted to the Animal Health Laboratory at the University of Guelph (Ontario, Canada) during 2009-2017 from 40 different geographic areas in Ontario. Using a previously described criterion of grouping strains with < 4-bp differences into the same molecular type (p146 type), the 113 clinical samples clustered into 19 p146 genotypes. Dominant types were found in 2016 and 2017 only, indicating that highly diversified M. hyopneumoniae strains existed in Ontario. Some strains from the same geographic location but different years had the same sequence types, indicating that the same strain types circulate persistently in the field. Different p146 genotypes were also identified from similar geographic locations, indicating that either M. hyopneumoniae strains are prone to mutation or that multiple strains can infect the same or nearby swine production units.