Molecular epidemiology of cases of Mycoplasma californicum infection in Japan.

Bovine mastitis due to Mycoplasma californicum is often accompanied by huge economic losses, and the disease spreads very quickly. An appropriate molecular epidemiological analysis is needed to prevent and control infectious disease, but molecular epidemiological analysis methods for M. californicum have not yet been reported. Here we developed a combination of multiple-locus variable-number tandem repeat analysis (MLVA) and pulsed-field gel electrophoresis (PFGE) methods, which are common genotyping methods for various bacteria, for M. californicum. The MLVA is based on four interspersed repeat units that were found in the M. californicum genome data. The MLVA using these repeat units showed sufficient discriminatory power for a molecular epidemiological analysis; i.e., a Hunter-Gaston diversity index (HGDI) of 0.949, against M. californicum strains in Japan and M. californicum strain ATCC 33461. The PFGE for M. californicum also showed sufficient discriminatory power, with an HGDI of 0.985. Strain ATCC 33461 showed MLVA profiles and pulsotypes that differed greatly from those of strains from Japan. These results indicate that MLVA and PFGE are good tools for identifying M. californicum transmission events more accurately. Our combined MLVA and PFGE analysis suggests the persistence of M. californicum infection among herds in a specific area for a long period of time, as well as the movement of cows and heifers accompanying the expansion of M. californicum infection. Failure to identify asymptomatic infected cows is suspected as one of the central causes of the present M. californicum infection scenario in Japan.