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

Abstract

Abstract 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 104 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.