The bacterial flora were determined qualitatively and quantitatively on samples taken at various stages of handling several species of fish of commercial importance in Queensland. There was an overall increase in the number of bacteria during handling and processing; both the composition and quantity of the bacterial flora of individual samples taken at each stage of handling varied widely. Members of the genus Micrococcus formed the major proportion of the flora of freshly caught fish. Pseudomonas and Moraxella spp. were predominant amongst the bacterial flora able to grow at 2° and constituted the bulk of the population in samples with high bacterial counts. This psychrophilic population was markedly reduced at the filleting stage. A medium prepared by the action of trypsin on a fish muscle homogenate was used to test bacterial isolates for their ability to produce odours. Forty‐three per cent of the pseudomonad isolates produced sulphydryl odours at 5°. Only small proportions of the other groups produced detectable odours. Members of the genus Pseudomonas were considered the most important fish spoilage bacteria under the conditions found in Queensland.
Pseudomonas‐like bacteria isolated from fresh and spoiling fish in southeastern Queensland were subjected to a wide range of physiological and nutritional tests. The results of these tests, together with those of 20 named strains, were analysed numerically, resulting in the formation of 11 groups. Most of the isolates clustered into group 1 and group 2 which also contained the bulk of the strains able to produce spoilage odours when grown in a tryptic digest of fish muscle at 2°C. Almost all of the group 1 organisms produced sulphydryl type odours, had only 50 mol % G + C and were identified as strains of Alteromonas putrefaciens which were deficient in the ability to produce H2S detectable in Peptone Iron Agar. Certain of the group 2 strains produced fruity and sulphydryl type odours, but these organisms were not distinguishable from other strains in this group not producing odours. Group 2 strains were highly related to Pseudomonas fragi and were intermediate in properties between Ps. fluorescens and Ps. putida. The remaining nine minor groups contained few organisms able to produce spoilage odours.
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