Abstract

Seafood-associated bacterial contamination is an important food-safety concern, particularly for shellfish that are exposed to aquatic environments and may accumulate microorganisms. This study evaluated bacterial contamination of five selected shellfish—mussel, periwinkle, blood clam, rock snail and oyster—and assessed the antibacterial activity of ethanolic garlic (Allium sativum), neem (Azadirachta indica) and clove (Syzygium aromaticum) extracts against representative seafood-associated bacteria. Bacterial loads were determined from the outer surface, inner fluid and intestine, while agar-well diffusion and broth dilution were used to assess plant-extract activity and minimum inhibitory concentration (MIC), respectively. The highest total heterotrophic bacterial load on the outer surface was recorded in mussel (7.3 ± 0.2 × 10⁶ CFU/cm²), while rock snail recorded the highest inner-fluid load (9.0 ± 0.2 × 10⁷ CFU/mL). Among the target bacteria, Vibrio spp. was detected at the highest levels in the inner fluid of mussel (1.8 × 10⁴ CFU/mL) and intestine of mussel (1.1 × 10⁴ CFU/g). E. coli was detected on the outer surface of oyster (5.6 × 10³ CFU/cm²) but was not detected in the inner fluid or intestine of the selected shellfish. Clove produced the greatest zones of inhibition across the concentration range, followed by garlic, whereas neem generally showed weaker activity. MIC values were 3.125, 3.125 and 6.25 mg/mL for clove against E. coli, V. parahaemolyticus and S. enterica, respectively; the corresponding values for garlic were 12.5, 6.25 and 25 mg/mL and for neem were 50, 25 and 50 mg/mL. The findings indicate substantial variation in bacterial contamination among shellfish and anatomical compartments and demonstrate promising in vitro antibacterial activity of clove and garlic extracts.