1036
whereas some were also present in the ventral tegmental area. No labelled cells were seen in the cerebral peduncle and superior cerebellar peduncle. Among positively hybridised cells (n 805), 95% (763) were the large neuromelanin-containing neurons. These data indicate that, within substantia nigra pars compacta, CuZn SOD gene is preferentially and highly expressed in the neuromelanin-pigmented neurons, a subset of cells vulnerable to degenerative processes in Parkinson’s disease.’ This observation suggests that within these cells biochemical pathways leading to generation of0*- radicals are especially active, thus needing a high CuZn SOD content to facilitate removal of these radicals. Alternatively, a high cellular CuZn SOD activity, by promoting H202 production, might also contribute to the vulnerability of these =
neurons.
Laboratory of Genetics Biochemistry, CNRS URA 1335,
Hôpital Necker-Enfants Malades, 75015 Paris, France
I. CEBALLOS
Laboratory of Experimental Medicine, INSERM U 289, Hôpital de la Salpétrière, Paris
M. LAFON F. JAVOY-AGID E. HIRSCH
Laboratory of Genetics Biochemistry, Hôpital Necker-Enfants Malades
A. NICOLE P. M. SINET
Laboratory of Experimental Medicine, Hôpital de la Salpétrière
Y. AGID
1. Hirsch
E, Graybiel AM, Agid Y. Melanized dopaminergic neurons are differentially susceptible to degeneration in Parkinson’s disease. Nature 1988; 334: 345-17. 2. Calne DB, Langston JW. Aetiology of Parkinson disease. Lancet 1983; ii. 1457-59. 3 Graham DG. Oxidative pathways for catecholamines m the genesis of neuromelanin and cytotoxic quinones. Mol Pharmacol 1978; 14: 633-34. 4. Dexter DT, Carter C, Agid F, et al. Lipid peroxidation as a cause of nigral cell death in Parkinson’s disease. Lancet 1986; ii. 639-40. 5. Martilla RJ, Lorentz H, Rinne UK. Oxygen toxicity protecting enzymes in Parkinson’s disease. J Neurol Sci 1988; 86: 321-31 6. Saggu H, Cooksey J, Dexter D, et al. A selective increase in particulate superoxide dismutase activity in parkinsonian substantia nigra J Neurochem 1989; 53: 692-97. 7. Ceballos I, Javoy-Agid F, Hirsch E, et al. Localization of copper zinc superoxide dismutase mRNA in human hippocampus by in situ hybridization Neurosci Lett 1989; 105: 41-46.
incubated at 30°C for 48 h. In parallel 1 ml of skin homogenate and a cavity swab were added to 20 ml of Oxoid tryptose phosphate broth and incubated at 5°C for 8 weeks before plating. With carcasses obtained on three occasions from the same slaughterhouse, a most probable number technique was used to determine levels of naturally occurring L monocytogenes. The method involved "hot" enrichment2 and plating on the Oxford medium, with incubation as above. Carcasses were examined by taking skin samples. Representative isolates were subjected to confirmatory tests.216 freshly processed carcasses were examined for naturally occurring L monocytogenes. 10 were positive, with counts of 0 36 to 24/cm2 (mean 4-3), which would have had little effect on the levels of artificial inocula. Inoculated carcasses were examined at 0, 7, 14, and 21 days when held at 5°C and 0, 3, 5, and 7 days for birds kept at 10’C, but in the following table results for all storage periods are combined: was
Proportion positive for L monocytogenes after storage at.
5°C 102 Time Before storage After storage
10°C 10’
102
10’
(CFU/cm2) (CFU/cm2) (CFU/cm2) (CFU /CM2) 0/3 0/3 1/33 0/3 3/9 1/9 0/9 4/9
Immediately after irradiation, only 1 of 12 carcasses was positive for L morwcytogenes and no further positives were found until day 14 at 5°C and day 5 at 10°C. On completion of each storage period, the carcasses remained unspoiled but 8/36 (22%) yielded L monocytogenes, mainly from the larger inoculum. At the lower inoculation level, which is more in keeping with natural contamination, only 1 of 18 carcasses showed any surviving listeria. At both 5°C and 10°C, counts on non-irradiated birds increased 100-fold after 7 and 3 days, respectively, but spoilage was becoming evident at 10°C and no further tests were made on birds held at this temperature. Spoilage of non-irradiated birds kept at 5°C was detectable after 7 days, by which time L monocytogenes had increased 1000-fold. Only very slow growth of any survivors was observed initially at either storage temperature for the irradiated birds; after 7 days at 10°C, counts had reached a mean of almost
1500/cm2. This
Survival and
growth of Listeria monocytogenes on irradiated poultry carcasses
SIR,-In the UK poultry carcasses are often contaminated with Listeria monocytogenes,1,2 a potential pathogen that can grow under chill conditions. Because irradiation is to be permitted in the UK and has been proposed as a means of eliminating listeria,3 we have investigated the effects of irradiation on the survival of L monocytogenes on poultry carcasses and on the behaviour of the organism during cold storage. Previous studies4-7 suggest that the susceptibility of L monocytogenes to irradiation is comparable with that of the salmonellae, and doses of 25-7-0 kGy should be sufficient to effect elimination. However, for chilled poultry doses above 25 kGy may affect the odour, colour, or flavour of the cooked 8
product. We used a mixture of four strains of L monocytogenes, isolated from poultry, to inoculate freshly processed, air-chilled broiler carcasses obtained from a commercial slaughterhouse. Inocula of about 100 or 10 000 colony-forming units/cm2 from diluted broth cultures, were spread over the surface of the carcass with an alginate swab. The abdominal cavity was also inoculated. The carcasses were then placed in double polythene bags, and those requiring irradiation were taken under refrigeration to a nearby treatment plant, where they were given 25 kGy gamma radiation from a cobalt-60 source. Irradiated and non-irradiated carcasses were stored at 5 or 10°C and individual birds were removed at suitable intervals for sampling. The experiment was done three times on different occasions. Carcasses were sampled by taking five 10 cmz portions of skin which were bulked and homogenised for diluting and plating directly on Oxoid listeria selective agar (Oxford formulation), which
study confirms that L monocytogenes is
common on raw
but shows that numbers are likely to be low poultry immediately after processing and that they will largely be destroyed by gamma irradiation at 25 kGy. Where survivors were found, after irradiation, they either recovered slowly from sublethal injury or multiplied to detectable levels from small numbers of uninjured cells. Because listerias seem to grow well on poultry skin at 5OC, any multiplication before irradiation would progressively reduce the chances of elimination from chilled carcasses, and our results do not support the contention of Huhtanen et aF that 20 kGy is sufficient to destroy 10 000 L monocytogenes on poultry. Listeria may sometimes grow under commercial conditions of transportation to a radiation treatment centre, and potential users of irradiation for chilled poultry should be aware of the possibility. carcasses
Bristol Laboratory, AFRC Institute of Food Research, Langford, Bristol BS18 7DY, UK
G. C. MEAD W. R. HUDSON RADZIAH ARIFFIN
1. Pini PN, Gilbert RJ. The occurrence in the UK of Lisieria species in raw chickens and soft cheeses. Int J Food Microbiol 1988, 6: 317-26. 2 Hudson WR, Mead GC. Listeria contamination at a poultry processing plant Lett Appl Microbiol 1989; 9: 211-14. 3. World Health Organisation. Foodborne listeriosis: report of a WHO informal working group (WHO/EHE/FOS 88 5). Geneva WHO, 1988. 4. Stegeman H. Radiation resistance of Listeria monocytogenes. 10th International Symposium on Listeriosis (Pecs, Hungary, Aug, 22-26, 1988 104 (abstr). 5. Tarjan V. The sensitivity of Listeria moncytogenes to gamma radiation 10th International Symposium on Listeriosis (Pecs, Hungary, Aug, 22-26, 1988) 105
(abstr). 6. Patterson M. Sensitivity of Listeria monocytogenes to irradiation on poultry meat and in phosphate-buffered saline Lett Appl Microbiol 1989, 8: 181-84 7. Huhtanen CN, Jenkins RK, Thayer DW Gamma radiation sensitivity of Listeria monocytogenes.J Food Protect 1989; 52: 610-13 8 Mulder RWAW. Salmonella radicidation of poultry carcasses Doctoral thesis, Spelderholt Institute for Poultry Research, Beekbergen, Netherlands, 1982
whereas some were also present in the ventral tegmental area. No labelled cells were seen in the cerebral peduncle and superior cerebellar peduncle. Among positively hybridised cells (n 805), 95% (763) were the large neuromelanin-containing neurons. These data indicate that, within substantia nigra pars compacta, CuZn SOD gene is preferentially and highly expressed in the neuromelanin-pigmented neurons, a subset of cells vulnerable to degenerative processes in Parkinson’s disease.’ This observation suggests that within these cells biochemical pathways leading to generation of0*- radicals are especially active, thus needing a high CuZn SOD content to facilitate removal of these radicals. Alternatively, a high cellular CuZn SOD activity, by promoting H202 production, might also contribute to the vulnerability of these =
neurons.
Laboratory of Genetics Biochemistry, CNRS URA 1335,
Hôpital Necker-Enfants Malades, 75015 Paris, France
I. CEBALLOS
Laboratory of Experimental Medicine, INSERM U 289, Hôpital de la Salpétrière, Paris
M. LAFON F. JAVOY-AGID E. HIRSCH
Laboratory of Genetics Biochemistry, Hôpital Necker-Enfants Malades
A. NICOLE P. M. SINET
Laboratory of Experimental Medicine, Hôpital de la Salpétrière
Y. AGID
1. Hirsch
E, Graybiel AM, Agid Y. Melanized dopaminergic neurons are differentially susceptible to degeneration in Parkinson’s disease. Nature 1988; 334: 345-17. 2. Calne DB, Langston JW. Aetiology of Parkinson disease. Lancet 1983; ii. 1457-59. 3 Graham DG. Oxidative pathways for catecholamines m the genesis of neuromelanin and cytotoxic quinones. Mol Pharmacol 1978; 14: 633-34. 4. Dexter DT, Carter C, Agid F, et al. Lipid peroxidation as a cause of nigral cell death in Parkinson’s disease. Lancet 1986; ii. 639-40. 5. Martilla RJ, Lorentz H, Rinne UK. Oxygen toxicity protecting enzymes in Parkinson’s disease. J Neurol Sci 1988; 86: 321-31 6. Saggu H, Cooksey J, Dexter D, et al. A selective increase in particulate superoxide dismutase activity in parkinsonian substantia nigra J Neurochem 1989; 53: 692-97. 7. Ceballos I, Javoy-Agid F, Hirsch E, et al. Localization of copper zinc superoxide dismutase mRNA in human hippocampus by in situ hybridization Neurosci Lett 1989; 105: 41-46.
incubated at 30°C for 48 h. In parallel 1 ml of skin homogenate and a cavity swab were added to 20 ml of Oxoid tryptose phosphate broth and incubated at 5°C for 8 weeks before plating. With carcasses obtained on three occasions from the same slaughterhouse, a most probable number technique was used to determine levels of naturally occurring L monocytogenes. The method involved "hot" enrichment2 and plating on the Oxford medium, with incubation as above. Carcasses were examined by taking skin samples. Representative isolates were subjected to confirmatory tests.216 freshly processed carcasses were examined for naturally occurring L monocytogenes. 10 were positive, with counts of 0 36 to 24/cm2 (mean 4-3), which would have had little effect on the levels of artificial inocula. Inoculated carcasses were examined at 0, 7, 14, and 21 days when held at 5°C and 0, 3, 5, and 7 days for birds kept at 10’C, but in the following table results for all storage periods are combined: was
Proportion positive for L monocytogenes after storage at.
5°C 102 Time Before storage After storage
10°C 10’
102
10’
(CFU/cm2) (CFU/cm2) (CFU/cm2) (CFU /CM2) 0/3 0/3 1/33 0/3 3/9 1/9 0/9 4/9
Immediately after irradiation, only 1 of 12 carcasses was positive for L morwcytogenes and no further positives were found until day 14 at 5°C and day 5 at 10°C. On completion of each storage period, the carcasses remained unspoiled but 8/36 (22%) yielded L monocytogenes, mainly from the larger inoculum. At the lower inoculation level, which is more in keeping with natural contamination, only 1 of 18 carcasses showed any surviving listeria. At both 5°C and 10°C, counts on non-irradiated birds increased 100-fold after 7 and 3 days, respectively, but spoilage was becoming evident at 10°C and no further tests were made on birds held at this temperature. Spoilage of non-irradiated birds kept at 5°C was detectable after 7 days, by which time L monocytogenes had increased 1000-fold. Only very slow growth of any survivors was observed initially at either storage temperature for the irradiated birds; after 7 days at 10°C, counts had reached a mean of almost
1500/cm2. This
Survival and
growth of Listeria monocytogenes on irradiated poultry carcasses
SIR,-In the UK poultry carcasses are often contaminated with Listeria monocytogenes,1,2 a potential pathogen that can grow under chill conditions. Because irradiation is to be permitted in the UK and has been proposed as a means of eliminating listeria,3 we have investigated the effects of irradiation on the survival of L monocytogenes on poultry carcasses and on the behaviour of the organism during cold storage. Previous studies4-7 suggest that the susceptibility of L monocytogenes to irradiation is comparable with that of the salmonellae, and doses of 25-7-0 kGy should be sufficient to effect elimination. However, for chilled poultry doses above 25 kGy may affect the odour, colour, or flavour of the cooked 8
product. We used a mixture of four strains of L monocytogenes, isolated from poultry, to inoculate freshly processed, air-chilled broiler carcasses obtained from a commercial slaughterhouse. Inocula of about 100 or 10 000 colony-forming units/cm2 from diluted broth cultures, were spread over the surface of the carcass with an alginate swab. The abdominal cavity was also inoculated. The carcasses were then placed in double polythene bags, and those requiring irradiation were taken under refrigeration to a nearby treatment plant, where they were given 25 kGy gamma radiation from a cobalt-60 source. Irradiated and non-irradiated carcasses were stored at 5 or 10°C and individual birds were removed at suitable intervals for sampling. The experiment was done three times on different occasions. Carcasses were sampled by taking five 10 cmz portions of skin which were bulked and homogenised for diluting and plating directly on Oxoid listeria selective agar (Oxford formulation), which
study confirms that L monocytogenes is
common on raw
but shows that numbers are likely to be low poultry immediately after processing and that they will largely be destroyed by gamma irradiation at 25 kGy. Where survivors were found, after irradiation, they either recovered slowly from sublethal injury or multiplied to detectable levels from small numbers of uninjured cells. Because listerias seem to grow well on poultry skin at 5OC, any multiplication before irradiation would progressively reduce the chances of elimination from chilled carcasses, and our results do not support the contention of Huhtanen et aF that 20 kGy is sufficient to destroy 10 000 L monocytogenes on poultry. Listeria may sometimes grow under commercial conditions of transportation to a radiation treatment centre, and potential users of irradiation for chilled poultry should be aware of the possibility. carcasses
Bristol Laboratory, AFRC Institute of Food Research, Langford, Bristol BS18 7DY, UK
G. C. MEAD W. R. HUDSON RADZIAH ARIFFIN
1. Pini PN, Gilbert RJ. The occurrence in the UK of Lisieria species in raw chickens and soft cheeses. Int J Food Microbiol 1988, 6: 317-26. 2 Hudson WR, Mead GC. Listeria contamination at a poultry processing plant Lett Appl Microbiol 1989; 9: 211-14. 3. World Health Organisation. Foodborne listeriosis: report of a WHO informal working group (WHO/EHE/FOS 88 5). Geneva WHO, 1988. 4. Stegeman H. Radiation resistance of Listeria monocytogenes. 10th International Symposium on Listeriosis (Pecs, Hungary, Aug, 22-26, 1988 104 (abstr). 5. Tarjan V. The sensitivity of Listeria moncytogenes to gamma radiation 10th International Symposium on Listeriosis (Pecs, Hungary, Aug, 22-26, 1988) 105
(abstr). 6. Patterson M. Sensitivity of Listeria monocytogenes to irradiation on poultry meat and in phosphate-buffered saline Lett Appl Microbiol 1989, 8: 181-84 7. Huhtanen CN, Jenkins RK, Thayer DW Gamma radiation sensitivity of Listeria monocytogenes.J Food Protect 1989; 52: 610-13 8 Mulder RWAW. Salmonella radicidation of poultry carcasses Doctoral thesis, Spelderholt Institute for Poultry Research, Beekbergen, Netherlands, 1982
