Preserved goat milk as a valid sample for the PCR detection of Mycoplasma agalactiae

Goat milk samples routinely obtained by milk distributing companies and quality control laboratories are preserved using azidiol (AZ) or bronopol (BR). This study was designed to determine if these treated goat milk samples are suitable for Mycoplasma (M.) agalactiae detection by PCR. The effects of these preservatives on the limits of M. agalactiae direct PCR detection were established using samples inoculated with mycoplasma cultures. Samples inoculated with a determined concentration of M. agalactiae showed no differences among the 3 preservation methods and in all cases the limits of detection of the PCR assays were 103 CFU ml. In addition, 300 bulk tank milk (BTM) samples from 45 herds from an infected area were each divided into three aliquots subjected to different preservation treatments (no preservative, NP, AZ or, BR) and then PCR tested. Of the 300 BTM samples, 43 different ones scored a positive result for M. agalactiae in at least one condition distributed in this way, 32 NP aliquots (74.4% of the positive samples), 27 BP aliquots (62.8%) and 27 AZ aliquots (62.8%). Among the three preservation methods, no significant differences were found (p > 0.05) and the difference in results was attributed to the sensitivity increasement when analyzing more than one time a BTM sample. These results suggest that the PCR technique can be used as a rapid diagnostic method to detect M. agalactiae in AZ or BR preserved goat milk samples. The possible use of such samples for health programmes would have considerable cost benefits.