[Study on the effects of HTST pasteurization temperatures on Mycobacterium avium subsp. paratuberculosis in an industrial fluid milk-processing system].

Johne disease is ruminant chronic granulomatous enteritis caused by Mycobacterium avium subsp. paratuberculosis (MAP). The domestic animals infected with this pathogen present severe weight loss due to chronic diarrhea and a reduction in lactation yield. These result in enormous economic loss since the affected animals are subsequently subject to artificial selections and disinfection of the environment are absolutely necessary. Furthermore, MAP has been suspected to have pathological relationship to Crohn's disease, human chronic granulomatous enteritis. The bacterium grows slower on solid culture and its colony becomes visible after two months of culture. In Japan, there has been almost no investigation on pasteurization temperature of commercial milk using MAP. It comes from the fact that the growth rate of MAP is very slow and that MAP is a related species to Mycobacterium tuberculosis, which pasteurization condition has been well defined. The studies on the pasteurization conditions of commercial milk have been mainly targeted to reduce the risk of infection to Coxiella and Mycobacterium tuberculosis. However, there has been a concern about the possibility that MAP is remained in pasteurized milk because MAPs form an aggregate and the bacterium at its center may not receive enough heat to get pasteurized. From these reasons, the present study aims to investigate validity of the current pasteurization conditions of commercial milk by implementing experimental pasteurization at various pasteurization temperatures using milk experimentally infected with MAP, and to clarify if MAP is eliminated at these temperatures in order to achieve smooth enforcement of the current ministry order. We conducted plant pasteurization experiment at four pasteurization conditions (high temperature, short time (HTST); 82, 77, 72 degrees C for 15 seconds and low temperature, long time (LTLT); 63 degrees C for 30 minutes) using two MAP strains, ATCC19698 and OKY-20. In conclusion, there appeared no colony of the two MAP strains formed from the milk pasteurized at the four pasteurization conditions examined.

The occurrence of Listeria monocytogenes in imported ready-to-eat foods in Japan.

Quantitative analyses of Listeria monocytogenes in imported ready-to-eat (RTE) foods sold at retail stores in Japan were performed. Of the 77 non-cooked meat products, 6 samples (7.8%) tested positive. The levels of contamination of 4 of the samples were below 100 colony-forming units (CFU)/g, which is the microbiological criterion for L. monocytogenes in RTE foods as determined by Codex. However, Listeria cells at levels of 100 and 400 CFU/g were detected in a salami sample and a raw ham sample, respectively. All of the 70 cheese samples and the 3 samples made from raw ham and cheese showed negative test results. These results suggest that imported RTE foods are potential sources of the causative agent of listeriosis.

Antimicrobial susceptibilities of Listeria monocytogenes isolated in Japan.

The antimicrobial susceptibility of 201 Listeria monocytogenes isolates from foods, environments, animals and human patients in Japan was determined. All isolates were susceptible to ampicillin, the first choice of drug for listeriosis treatment, chloramphenicol, dihydrostreptomycin, erythromycin, enrofloxacin, gentamicin, kanamycin, lincomycin, nosiheptide, salinomycin, vancomycin, and virginiamycin. A human strain was resistant to oxytetracycline. The Minimum Inhibitory Concentration (MIC) for 50% of the strains and the MIC for 90% of the strains were comparable in all the isolates. This is the first investigation to compare antibiotic resistances between isolates from foods and isolates from human patients in Japan. The result showed that most of the isolates were susceptible to antibiotics used in this study.