Investigation of the impact of simulated commercial centrifugation and microfiltration conditions on levels of Mycobacterium avium subsp. paratuberculosis in milk

The potential for physical removal of Mycobacterium avium ssp. paratuberculosis (M. paratuberculosis) from milk by centrifugation and microfiltration was investigated by simulating commercial processing conditions in the laboratory by means of a microcentrifuge and syringe filters, respectively. Results indicated that both centrifugation of preheated milk (60 degrees C) at 7000 x g for 10 s, and microfiltration through a filter of pore size 1.2 mu m, were capable of removing up to 95-99.9% of M. paratuberculosis cells from spiked whole milk and Middlebrook 7H9 broth suspensions, respectively. Centrifugation and microfiltration may therefore have potential application within the dairy industry as pretreatments to reduce M. paratuberculosis contamination of raw milk.

Interaction between Mycobacterium avium subsp. paratuberculosis and environmental protozoa

Background: Interactions between Mycobacterium avium subsp. paratuberculosis (Map) and free-living protozoa in water are likely to occur in nature. The potential impact of ingestion of Map by two naturally occurring Acanthamoeba spp. on this pathogen's survival and chlorine resistance was investigated. Results: Between 4.6 and 9.1% of spiked populations of three Map strains (NCTC 8578, B2 and ATCC 19698), which had been added at a multiplicity of infection of 10: 1, were ingested by Acanthamoeba castellanii CCAP 1501/1B and A. polyphaga CCAP 1501/3B during co-culture for 3 h at 25 C. Map cells were observed to be present within the vacuoles of the amoebae by acid-fast staining. During extended co-culture of Map NCTC 8578 at 25 degrees C for 24 d with both A. castellanii and A. polyphaga Map numbers did not change significantly during the first 7 days of incubation, however a 1-1.5 log(10) increase in Map numbers was observed between days 7 and 24 within both Acanthamoeba spp. Ingested Map cells were shown to be more resistant to chlorine inactivation than free Map. Exposure to 2 mu g/ml chlorine for 30 min resulted in a log(10) reduction of 0.94 in ingested Map but a log(10) reduction of 1.73 in free Map (p <0.001). Conclusion: This study demonstrated that ingestion of Map by and survival and multiplication of Map within Acanthamoeba spp. is possible, and that Map cells ingested by amoebae are more resistant to inactivation by chlorine than free Map cells. These findings have implications with respect to the efficacy of chlorination applied to Map infected surface waters.

Mycobacterium avium ssp. paratuberculosis: its incidence, heat resistance and detection in milk and dairy products

Mycobacterium avium ssp. paratuberculosis (MAP) causes Johne's disease in cattle and other ruminants and has been implicated as a possible cause of Crohn's disease in humans. The organism gains access to raw milk directly through excretion into the milk within the udder and indirectly through faecal contamination during milking. MAP has been shown to survive commercial pasteurization in naturally infected milk, even at the extended holding time of 25 s. Pasteurized milk must therefore be considered a vehicle of transmission of MAP to humans. isolation methods for MAP from milk are problematical, chiefly because of the absence of a suitable selective medium. This makes food surveillance programs and research on this topic difficult. The MAP problem can be addressed in two main ways: by devising a milk-processing strategy that ensures the death of the organism: and/or strategies at farm level to prevent access of the organism into raw milk. Much of the research to date has been devoted to determining ifa problem exists and, if so, the extent of the problem. Little has been directed at possible solutions. Given the current state of information on this topic and the potential consequences for the dairy industry research is urgently needed so that a better understanding of the risks and the efficacy of possible processing solutions can be determined.