Rapid quantitative monitoring method for the fish spoilage bacteria Pseudomonas

Pseudomonas spp. is a group of microorganisms commonly found in fish and other fresh foods and is involved in their spoilage process. The aim of this study was to develop a rapid and accurate quantitative assay for Pseudomonas spp. in fish using real-time PCR. The assay targets the carbamoyl phosphate synthase gene (carA) with SYBR green based real-time PCR. The selectivity of the assay was confirmed using 24 Pseudomonas strains and 55 non-pseudomonad strains. A linear quantification was established over seven orders of magnitude, from 40 – 4⁷ copies reaction⁻¹. The assay was validated on cod samples collected during two shelf life trials and showed a high degree of correlation to the plate count method (rP = 0.891) where the difference between the methods was 0.04 log₁₀ CFU g⁻¹ on average. The study shows that it is possible to quantify accurately the specific spoilage organisms belonging to the genus Pseudomonas in fish using real-time PCR. The method takes less than 5 h from sampling to results. The short detection time of the method can provide the fish industry with an important tool for quality control and processing management.