Pasteurization: Effective Reduction of Prototheca Human Health Risk?

Tanya Lynne Farrington-Thomason


Prototheca is an achlorophyllic alga which has potential to cause disease in humans and animals. Dairy cattle particularly can be affected by Prototheca in their environment and may suffer from mastitis and systemic infections. Dogs and humans are also susceptible to prototheca infection. Prototheca is not always killed using standard pasteurization techniques. The prevalence and impact of prototheca in Maine dairies has not been investigated. After surveying dairy farms in the State of Maine, 9 farms were identified as being prototheca positive. Isolates were cultured using selective culture media, and were identified as to both genus and species using a nested PCR assay. A simulated pasteurization technique was then used to evaluate the sensitivity of these isolates to standard methods used in the dairy processing industry. Standard methods of pasteurization utilized were heating to 63°C for 30 minutes and 72°C for 15 seconds. A heat block was used for the heating process. An ice-water bath was used for cooling of heated tubes and for positive control tubes. Of 14 Maine isolates and 7 ATCC type strains tested, 100% showed sensitivity to both methods. However, 20.7% of samples from the 63°C/30 minute treatment and 15.1% of samples from the 72°C/15 second treatment did not have 100% kill.