Preprint volume - SIBM

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Microbiol) and incubated at 28 °C and 40 °C for 24-48 h and on Pseudomonas agar F
medium (Liofilchem) at 37 °C for 24 h in order to identify the presumptive genera
Vibrio and Pseudomonas respectively. The colonies which grew on TCBS agar and
showed a yellow or greenish colour were indicative for presumptive Vibrio species
while the colonies which grew on Pseudomonas agar F medium, appeared surrounded
by a yellow to greenish-yellow zone and produced a bright green colour which
fluoresces under UV light, were considered to belong to the P. aeruginosa sp.
Results - The microbiological quantitative analyses showed the following mean
values: the counts of aerobic heterotrophic viable bacteria proved to be 1521 cfu/g
(from 0 to 8550), Enterobacteriaceae were 409 cfu/g (from 0 to 4250) and Coliforms
were 187 cfu/g (from 0 to 1405). As regards the counts of probiotics observed on MRS
medium, only 6 out of 30 intestinal samples showed the presence of bacteria able to
growth on this medium with a mean number of 5 cfu/g (from 0 to 6). The qualitative
characterisation of 100 colonies by basic phenotypic tests, indicated that the dominant
microflora was constituted of 77 Gram negative microorganisms (75 rod-shaped
bacteria and 2 coccal shaped ones). Twenty-three out of 100 isolates proved to be
Gram positive (17 rods, 6 cocci and 1 spore forming rod-shaped microorganism). Most
of the isolates were catalase positive. On the base of the growth, the diameter and the
colour of the colonies observed on selective media used, we found one group of
presumptive Vibrio (27%) which merged both mesophylic (21%) and thermophylic
bacteria (6%), a second group of P. aeruginosa strains (7%) and an unidentified group
(39%).
Conclusions - The quantitative microbiological analyses of the intestine of Sparus
aurata examined evidenced higher values of bacteria than what found in the intestine
of seabreams reared in floating cages (Floris et al., 2009). However, these values
proved quite low if compared with other studies performed on a different fish species
(Al-Harbi et al., 2004). These results demonstrate how the bacterial flora is influenced
by various factors which are worth to be monitored. The qualitative analyses of
intestinal microflora showed a dominance of Gram negative bacteria. The bacterial
intestinal load detected in this study indicates the good quality of both fish and the
water where the seabreams live. Further studies are being conducted by means of 16S
rDNA analysis in order to identify all the bacterial isolates at species level.
Acknowledgements: The authors thank the “Cooperativa Pescatori Tortoli” for their collaboration.
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