Bacteriological analysis toArca noae (Linnaeus, 1758) in the South of Italy: the first record of halophilic Vibrio

Arca noae is one of four commercially exploited bivalves in the eastern Adriatic and it is a common dish in many Italian, Slovenian and Croatian regions, as both a raw and lightly cooked foodstuff. In this study, Arca noae samples collected along the Tyrrhenian coast near Patti (Sicily, Italy) were examined in order to assess their bacteriological characteristics and suitability for consumption. The total viable microrganisms (TVM), halophilc bacteria (HB), faecal coliforms, enterococci, Escherichia coli, Aeromonas hydrophila, Vibrio spp., and Salmonella spp. were determined. Presumptive Vibrio colonies were initially identified using biochemical tests, and strains identified as V. parahaemolyticus and V. alginolyticus were subsequently examined by PCR for the presence of different regulatory or virulence genes (toxR, toxRS, tl, trh, and tdh). In all samples, TVM and HB were very low ranging from 2.30 ± 0.35 to 3.52 ± 0.15 log cfu.g-1 and from 2.95 ± 0.22 to 3.65 ± 0.41 log cfu.g-1, respectively. Other bacteriological determinations were below the detection limits. The levels of Vibrio spp. contamination ranged from < 1.0 log cfu.g-1 (69.23% of samples) to 2.60 ± 0.31 log cfu.g-1. The qualitative method revealed the contamination of different potentially pathogenic Vibrio spp. in 86.41% of the samples. V. alginolyticus (55.56%) and V. parahaemolyticus (31.11%) were the most common species. All V. parahaemolyticus isolates were positive for the tl gene, while 78.57% were toxR(+), 14.21% toxRS(+), and only 7.14% toxR(+) toxRS(+). Among V. alginolyticus strains, 32% were toxR(+) and 4% toxR(+) toxRS(+). To our knowledge, this is the first report on the isolation of V. parahaemolyticus strains from A. noae bivalves collected along the Italian coasts. The results indicate that potentially pathogenic vibrios are frequently found in A. noae, despite the remaining low microbiological content, suggesting that routine examination of bivalve molluscs for these pathogenic agents is advisable.