Evaluation of the susceptibility of Prototheca zopfii to milk pasteurization

Protothecosis has been reported in humans (gastroenteritis, bursitis, etc.) and in many other animal species. Bovine mastitis represents the main form of occurrence of protothecosis in cattle. Milk as well as dairy products, when contaminated with Prototheca spp., represent a potential means of tran smission of this zoonosis. The purpose of this study was to evaluate the su sceptibility of forty Prototheca zopfii strains isolated from milk from int ramammary infections in dairy cows and also from bulk milk tanks of dairy f arms, to the different ratios of temperature/time employed in the thermal t reatment of milk: 72-75 degrees C/1 5 seconds, 72-75 degrees C/20 seconds a nd 62-65 degrees C/30 minutes. The samples were subjected to these differen t temperature/time ratios. The evaluation of the thermal susceptibility of the P. zopfii strains showed that 34 strains were resistant in at least one of the tests. The results point out the need to consider the importance of mastitis caused by Prototheca spp. as representing a public health risk.