Abstract
The use of CTC makes the naturally occurring resistant bacteria predominant in the treated fish during storage3). If CTC is to be used constantly it would be necessary to give sufficient consideration to antagonism between resistant and sensitive bacteria.
Experiments were made concerning the antagonism between CTC-sensitive and an invitro resistant strain of Pseudomonas fluorescens, a typical organism associated with putrefaction of marine fish, or a naturally occurring resistant strain of Pseudomonas, isolated from the CTC-treated fish.
Results may be summarized as follows:
1. In mixed cultures of sensitive and resistant cells, it was noted that without the presence of CTC the resistant bacteria were inhibited when the mixing ratio was 1:1. The larger was the ratio, the more conspicuous the antagonism was (Table 1 and 3).
2. In the presence of 1 ppm CTC, which was far less than the maximum tolerance level of the sensitive organisms tested, resistant organisms became predominant even in a 1:1 mixture (Table 2 and 4).
Even if a tetracycline is used repeatedly, putrefactive bacteria are expected to develop very low resistance1), 2). Nevertheless, sufficient attention should be paid to such possibility. It is not likely that naturally occurring resistant bacteria become predominant in nature, considering the growth antagonism between sensitive and resistant bacteria.
