Research – Effect of Sodium Hypochlorite on Biofilm-Forming Ability of Histamine-Producing Bacteria Isolated from Fish

Histamine poisoning occurs when temperature-abused marine fish containing elevated levels of histamine are consumed. Histamine-producing bacteria found in fish can colonize processing surfaces and form biofilms. In this study, the biofilm-forming abilities of histamine-producing bacteria from Indian mackerel (Rastrelliger kanagurta) and the effect of hypochlorite treatment on biofilm formation were studied. The isolates of this study produced histamine in the range of 471 to 2,126 ppm. The histidine decarboxylase gene hdc was detected in all isolates producing histamine except in one strain each of Psychrobacter pulmonis and Proteus vulgaris. All isolates tested in this study produced moderate biofilms under control conditions, whereas exposure to 1 and 3 ppm of sodium hypochlorite significantly enhanced biofilm formation. However, exposure to 5 ppm of sodium hypochlorite showed an inhibitory effect on biofilm formation by all the isolates except Klebsiella variicola. The results of this study suggest that histamine-producing bacteria can form stable biofilms and that this activity may be enhanced by the application of low levels of sodium hypochlorite, a phenomenon that might influence the persistence of histamine-producing bacteria in fish processing areas.

• Bacteria isolated from Indian mackerel produced histamine in the range of 471 to 2,126 ppm.

• Histamine-producing bacteria isolated from the same fish can vary in the levels of histamine produced.

• The hdc gene was not detected in one strain each of Psychrobacter pulmonis and Proteus vulgaris.

• All histamine-producing bacteria formed moderate biofilms under control conditions.

• Exposure to 1 and 3 ppm of sodium hypochlorite increased biofilm formation by histamine-producing bacteria.