Development of a relative quantification real-time PCR assay for infection status investigation of Mycoplasma hyopneumoniae and Mycoplasma hyorhinis in nursery and finished pigs

Background: Swine enzootic pneumonia (SEP) is an important disease causing severe economic losses in the pig industry. The SEP-like lesions are common in nursery and finishing pigs suffered porcine respiratory disease complex (PRDC) and can be caused by not only Mycoplasma hyopneumoniae ( M. hyopneumoniae ) but also Mycoplasma hyorhinis ( M. hyorhinis ). This study aimed to develop a relative quantitative real-time PCR assay to investigate the M. hyopneumoniae and M. hyorhinis load in SEP-like lesions of nursery and slaughter pigs. Results The detection limit of the relative quantitative real-time PCR assay was 10 4 copies/µL. This assay had excellent specificity and showed no cross-reaction with other common swine viral and bacterial pathogens. M. hyorhinis detection rate (63.9%, 133/208) of nursery pigs was significantly higher than M. hyopneumoniae (2.4%), co-infection (24%) (p < 0.0001). The relative quantification ratios of M. hyorhinis in nursery pigs (1.196 ± 0.339) were significantly higher than that of M. hyopneumoniae (0.66 ± 0.26) (p < 0.0001) and that of M. hyorhinis in finishing pigs (0.477 ± 0.17) (p < 0.0001). In contrast, the relative quantification ratios of M. hyopneumoniae in finishing pigs (0.772 ± 0.229) were significantly higher than that of M. hyorhinis (0.477 ± 0.17) (p < 0.0001). Conclusions This study firstly developed a M. hyopneumoniae and M. hyorhinis multiplex relative quantification real-time PCR assay to point out the importance of M. hyorhinis as the major pathogen of SEP-like lesion in nursery pigs.