Comparison of culture and PCR to detect Mycoplasma agalactiae and Mycoplasma mycoides subsp. capri in ear swabs taken from goats

This study was designed to evaluate the validity of PCR for the direct detection of Mycoplasma (M.) agalactiae and Mycoplasma mycoides subsp. capri (Mmc), as the two species most frequently causing contagious agalactia (CA) in goats. The PCR method was compared with the traditional culture technique to determine which method was most efficient at identifying all auricular carriers present in herds. The samples analyzed were 307 ear swabs taken from goats reared in a CA endemic area. We assessed the validity of each technique to detect each species and agreement between both methods. For each species, the result was taken as true-positive when at least one of the two tests was positive. Of the swabs tested, 246 were scored positive by PCR (235 and 11 for Mmc and M. agalactiae, respectively) and 117 showed a positive culture result (113 for Mmc and 4 for M. agalactiae). 133 of the PCR-positive samples (124 and 9 for Mmc and M. agalactiae, respectively) yielded negative culture results and 4 culture-positive samples tested negative using PCR (2 for each species). Sensitivity and negative predictive values for PCR were 84.62 and 99.32 (for M. agalactiae) and 99.16 and 97.22% (for Mmc) respectively, and for culture were 30.77 and 97.03 (for M. agalactiae) and 47.08 and 36.08% (for Mmc), respectively. PCR proved to be a rapid and sensitive method for the detection of mycoplasmas in the external ear of asymptomatic carriers. Tools such as this are needed to adopt efficient control measures against CA.