Evaluation of psychrophilic, mesophilic, histamine forming bacteria and biogenic amine content in the muscle of mud spiny lobster,Panulirus polyphagus(HERBST, 1793) during ice storage

Detection, Identification, and Inactivation of Histamine-forming Bacteria in Seafood: A Mini-review

Seafood is one of the essential sources of nutrients for the human diet. However, they can be subject to contamination and can cause foodborne illnesses, including scombroid fish poisoning caused by histamine. Many microorganisms can produce enzymes that eventually decompose endogenous histidine to histamine in postmortem fish muscles and tissues. One of these is histamine-forming bacteria (HFB), primarily found in the gills, gut, and skin of fishes. Previous studies linked a plethora of Gram-negative HFB including Morganella spp. and Photobacterium spp. to scombroid fish poisoning from many types of seafood, especially the Scombridae family. These bacteria possess the hdc gene to produce histidine decarboxylase enzyme. It was reported that Gram-negative HFB produced 6345 ppm in tuna and 1223 ppm in Spanish mackerel. Interestingly, Gram-positive HFB have been isolated in the seafood samples with lower histamine levels. It suggests that Gram-negative HFB are the major contributor to the accumulation of histamine in seafood. Several analytical methods are available to detect and identify HFB and their histamine metabolites from seafood substrates. Rapid test kits can be used in food production settings for early detection of histamine to avoid food intoxication. Furthermore, high hydrostatic pressure and irradiation treatment could prevent the proliferation of HFB and inactivate the existing histidine decarboxylase (HDC) activity. As demonstrated in different seafood model systems, the HDC activity was deactivated at a maximum high hydrostatic pressure level of 400 MPa. The complete inactivation of HFB was achieved by gamma irradiation at a dose of 4.0 kGy. Other postharvest treatments, like enzymatic degradation and electrolyzed oxidizing water, were studied as sustainable methods for bacterial growth prevention and enzyme inactivation. However, other HFB react differently to these treatment conditions, and further studies are recommended.

Microbiome data reveal significant differences in the bacterial diversity in freshwater rohu (Labeo rohita) across the supply chain in Dhaka, Bangladesh

The present study aimed to characterize and compare the skin and gut microbial communities of rohu at various post-harvest stages of consumption using quantitative real-time polymerase chain reaction and 16S rRNA-based amplicon sequencing. Real-time PCR amplification detected higher copy numbers for coliform bacteria-Escherichia coli, Salmonella enterica and Shigella spp. in the marketed fish-compared to fresh and frozen samples. The 16S rRNA data revealed higher alpha diversity measurements in the skin of fish from different retail markets of Dhaka city. Beta ordination revealed distinct clustering of bacterial OTUs for the skin and gut samples from three different groups. At the phylum level, Proteobacteria was most abundant in all groups except the Fusobacteria in the control fish gut. Although Aeromonas was found ubiquitous in all types of samples, diverse bacterial genera were identified in the marketed fish samples. Nonetheless, low species richness was observed for the frozen fish. Most of the differentially abundant bacteria in the skin samples of marketed fish are opportunistic human pathogens enriched at different stages of postharvest handling and processing. Therefore, considering the microbial contamination in the aquatic environment in Bangladesh, post-harvest handling should be performed with proper methods and care to minimize bacterial transmission into fish.

Evaluating Sardinella brasiliensis quality indicators through the quantification of histamine and bacterial communities

Primarily formed by the microbial decarboxylation of the amino acid histidine, histamine is the leading global cause of food poisoning from fish consumption worldwide. In the present work, the quality of 12 fresh and 12 frozen marketed sardines (Sardinella brasiliensis) were evaluated for histamine concentration using High-performance Liquid Chromatography with Diode-Array Detection (HPLC-DAD), while the detection and quantification of histamine-producing bacteria were performed via quantitative Polymerase Chain Reaction (qPCR), and the microbiota composition of sardines was assessed through amplification of the 16S rRNA gene using high-throughput sequencing (HTS). According to the results obtained by HPLC-DAD, histamine concentration ranged from 226.14 to 583.87 mg kg⁻¹. The histidine decarboxylase (hdc) genes from gram-negative bacteria (Morganella morganii, and Enterobacter aerogenes) were identified. The most abundant microorganisms present in fresh sardines belong to the genera Macrococcus spp., Acinetobacter spp., and Pseudomonas spp., while the genera Phyllobacterium spp., Pseudomonas spp., and Acinetobacter spp. were most abundant in frozen sardines.