The consequences of antibiotic use in horticulture.

The problem of antibiotic resistance emerging from the use and misuse of antibiotics in veterinary practice was considered as long ago as the 1960s by the famous Swann Committee. 1 What seems to be less well understood, and certainly less well documented, is the use of antimicrobials in the world of plant science. Antibiotics have been widely used in the control of contamination of micropropagation and plant tissue culture for 40 years or so 2 and for a similar length of time in the topical treatment of bacterial diseases of fruit trees. 3 It is probably time to bring this to the attention of medical microbiologists. The first symposium to consider the problem of bacterial contamination and its control in plant tissue culture was held in Cork, Ireland, in 1987. 4 The concept of propagation, on agar, of plant tissues from fast growing tissue such as apical meristems has been well established for many decades. In the same way as virologists incorporate antimicrobials into their tissue culture media to control bacterial and fungal growth, so plant prop-agators have included such agents in their agar media. What is relatively new, however, is the massive scale on which plant material is now propagated and the consequent financial importance of the industry in the supply of plants for house, garden and agriculture. When plants are propagated in their hundreds of thousands, the prospect of bacterial contamination of even a small proportion is clearly costly. Plant tissue is normally prepared for propagation aseptically with sterile instruments in a clean air environment. The plant material is usually decontaminated with hypochlorite or another suitable 'antiseptic'. The tissue is placed on a special medium (usually that developed by Murashige & Skoog, 5 of which there are now many variations) and as it grows and develops it is transplanted on to agars of differing composition until the rooted plant is suitable for hardening off and planting in compost. All reports of the prophylactic use of antimicrobials by incorporating them in the culture media are prefaced by a statement to the effect that antibiotics should not replace sound aseptic technique. The problem is that the use of antibiotics in this way certainly conflicts with the normal principles of prophylactic use, in that the 'pathogen' is unknown and of uncertain susceptibility and the period of administration is prolonged. Plant tissue culture media are fairly hostile, at least to bacteria, particularly …