ISHS Acta Horticulturae 779: International Symposium on Growing Media
MICRO-ORGANISMS OF HUMAN HEALTH IMPORTANCE IN GROWING MEDIA |
| Authors: | W.R. Carlile, S.J. Hammonds |
| Keywords: | peat, bark, Legionella, coliforms, E. coli, Salmonella, antagonism |
| Abstract:
During the last decade, pressure from environmental lobbies to restrict the use of peat in the UK has led to an increase in the use of alternative materials such as timber wastes, green composts and composted bark. Epidemiological studies conducted in Australia in the late 1980s and early 1990s demonstrated a link between illness among elderly gardeners and the use of growing media based on composted bark, although the species from which bark is derived are very different in Australia compared to those in Western Europe. Pathological effects were attributed to elevated levels of human pathogens including species of Legionella, notably L. longbeachae. The legionella bacteria have also been detected in growing media in California, New Zealand and Japan. In view of the detection of micro-organisms such as Legionella spp. noted above, media from the UK have been investigated for the presence and levels of human pathogens. The incidence and survival of micro-organisms that may cause problems to public health has formed part of studies into microbial activity in growing media at Nottingham Trent University from 1995 to the present. Investigations have included studies on Escherichia coli, Salmonella typhimurium and Legionella spp. in a range of peat-based and non-peat based media. The presence of Legionella spp. has not been conclusively demonstrated in any media examined over the period of study. Coliforms have often been isolated from media, but at levels that constitute a very low risk to public health. These organisms, and another pathogen, Salmonella typhimurium, were able to survive for a month or more in heat-sterilised, inoculated media. Patterns of survival differed in inoculated unsterilised media: in most cases populations of the bacteria declined. This decline was far more marked in composted materials than in peat-based media. The antagonistic properties of some composted materials to plant pathogens are well known, and it appears that this antagonism may also extend to micro-organisms that have the capacity to cause disease in human beings. | |
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