Additionally these workers marked an isolate of Aer salmonicida with the xylE

Additionally these workers marked an isolate of aer

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Additionally, these workers marked an isolate of Aer. salmonicida with the xylE gene, using the plasmid pLV1013. This isolate was culturable on TSA from normal (non- sterile) lake water for three weeks, after which non-culturability developed, with the NCBV cells retaining chromosomal and plasmid DNA. The NCBV state can be postponed (60 days was mentioned by Pickup et ai, 1996) by the addition of high levels of nutrient, especially 125 |iM quantities of the amino acids arginine and methionine, to experimental microcosms. Aer. salmonicida decreased in size and became rounded, but were still culturable (Pickup et ai, 1996). The development of a dormant, non-culturable state of Aer. salmonicida in seawater at 4°C was apparent from the work of Ferguson et al. (1995). These workers incorporated a luciferase gene, luxAB, from V. fischeri into Aer. salmonicida and followed the fate of the cells. As before, intact, non-culturable cells could not be resurrected. There has always been a dilemma about the relevance of cells that cannot be cultured to fish. It is worth heeding the results of Stanley et al. (2002), who deter- mined that only culturable cells in laboratory microcosms could induce furunculosis upon injection into fish, and not PCR- or ELISA-positive samples which could not be supported by culturing evidence. Ecology of Aeromonas salmonicida an explanation To develop some previous points, there is tentative evidence to support the possibiHty that Aer. salmonicida undergoes sufficient modifications to its morphology in sea- water so as to be only recoverable on specialised media. Thus, while conducting experiments on the survival of Aer. salmonicida in seawater, Effendi and Austin (1991) found that samples where the pathogen was believed to be absent (or uncultur- able) actually contained cells which passed through 0.22 and 0.45 |im pore size porosity filters. These isolates grew on speciaHsed media designed for the recovery of L-forms, and showed agreement with the characteristics of Aer. salmonicida L-forms as reported by Mcintosh and Austin (1988, 1990a, 1991b). Subsequently, Aer. salmonicida colonies developed on basal marine agar (BMA) plates inoculated with material from turbid L-form broth medium. On this basis, Effendi and Austin (1991) recorded populations of ca. 10^ Aer. salmonicida cells/ml in the microcosms after corresponding enumeration of colonies on BMA had reached zero. Thus, they suggested that the existence of speciaHsed forms, e.g. L-forms, of Aer. salmonicida, may be a factor in the difficulties previous researchers have experienced in attempts to recover the pathogen from environmental samples. Continuing this theme, Effendi and Austin (1995a) examined the characteristics of the so-called NCBV cells. Using a marine microcosm, it was observed that these NCBV cells became much smaller and coccoid while retaining respiratory activity as measured by the reduction of tetra- zoliums to insoluble formazans. There was not any alteration in the LPS composition of the cells, but an alteration in the protein composition was recorded, with a reduction in some (15, 17, 22, 30 and 70kDa proteins) and an increase in a 49kDa
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  • Bacteria, representative, gram-negative bacteria

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