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−1 when mycoplasmas were resuspended in PBS and from 102 to 103 CCU ml−1 when 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.