Development of a specific immunomagnetic capture‐PCR for rapid detection of viable Mycoplasma agalactiae in sheep milk samples

AIMS: To develop an immunomagnetic capture (IMC) to detect viable Mycoplasma agalactiae in routine ovine milk samples. METHODS AND RESULTS: Polyclonal antibodies against two M. agalactiae membrane surface proteins (P80 and P55) were covalently conjugated to magnetic beads (MBs) to form MB‐Ab80 and MB‐Ab55. Mycoplasma agalactiae cells were captured by a specific antigen–antibody reaction and magnetic separation. Immunomagnetic capture (IMC) was used to isolate and concentrate M. agalactiae in serial decimal dilutions and in artificially contaminated milk to facilitate subsequent detection by PCR. A 375‐bp fragment of M. agalactiae was amplified using a pair of M. agalactiae‐specific primers in PCR. The limit of detection of IMC‐PCR method ranged from 10 to 10² CCU ml⁻¹when mycoplasmas were resuspended in PBS and from 10²to 10³ CCU ml⁻¹when mycoplasmas were resuspended in uncontaminated ovine milk. This study also describes the application of IMC‐PCR method to test for M. agalactiae in 516 milk samples collected from sheep with suspected contagious agalactia. Its performance was evaluated relative to culture. CONCLUSIONS: This report has demonstrated for the first time, the effective use of rapid and reliable IMC combined with PCR assay for the detection of viable M. agalactiae. SIGNIFICANCE AND IMPACT OF THE STUDY: The method IMC‐PCR provides an alternative to conventional microbiological detection, method and it could be applied to quick detection of M. agalactiae in routine sheep milk samples.