Prevalence of histidine decarboxylase genes of Gram-positive bacteria in surströmming as revealed by qPCR

Histamine is a degradation product of the bacterial decarboxylation of the amino acid histidine; such activity is determined by histidine decarboxylase encoded by a gene cluster, carried by some Gram-positive bacteria, that includes the hdcA gene. In this study, the presence of the hdcA gene in ready-to-eat surströmming samples collected from three producers based in Sweden was directly assessed via qPCR analysis for the very first time. Samples from producer A showed hdcA average gene abundance of 6.67±0.13 Log cells/gene copies g-1; in samples from producer B the average value attested at 5.56±0.06 Log cells/gene copies g-1, whereas for samples of producer C hdcA average gene abundance attested at 5.30±0.08 Log cells/gene copies g-1. ANOVA showed a significantly higher average hdcA gene copy number in samples from producer A, whereas no significant differences were seen between average values of hdcA gene copy numbers detected in samples from producer B and C. The hdcA gene copies detected in the present study could give an estimation of the load of potential histamine-producing bacteria in surströmming.