Molecular Characterization of Histamine-Producing Psychrotrophic Bacteria Isolated from Red Octopus (Octopus maya) in Refrigerated 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.

Molecular Mechanisms of Scombroid Food Poisoning

Scombroid food poisoning (SFP) is a foodborne disease that develops after consumption of fresh fish and, rarely, seafood that has fine organoleptic characteristics but contains a large amount of exogenous histamine. SFP, like other food pseudo-allergic reactions (FPA), is a disorder that is clinically identical to allergic reactions type I, but there are many differences in their pathogenesis. To date, SFP has been widespread throughout the world and is an urgent problem, although exact epidemiological data on incidence varies greatly. The need to distinguish SFP from true IgE-associated allergy to fish and seafood is one of the most difficult examples of the differential diagnosis of allergic conditions. The most important difference is the absence of an IgE response in SFP. The pathogenesis of SFP includes a complex system of interactions between the body and chemical triggers such as exogenous histamine, other biogenic amines, cis-urocanic acid, salicylates, and other histamine liberators. Because of the wide range of molecular pathways involved in this process, it is critical to understand their differences. This may help predict and prevent poor outcomes in patients and contribute to the development of adequate hygienic rules and regulations for seafood product safety. Despite the vast and lengthy history of research on SFP mechanisms, there are still many blank spots in our understanding of this condition. The goals of this review are to differentiate various molecular mechanisms of SFP and describe methods of hygienic regulation of some biogenic amines that influence the concentration of histamine in the human body and play an important role in the mechanism of SFP.

Polylactic Acid Film Coated with Electrospun Gelatin/Chitosan Nanofibers Containing Betel Leaf Ethanolic Extract: Properties, Bioactivities, and Use for Shelf-Life Extension of Tilapia Slices

Gelatin/chitosan solutions incorporated with betel leaf ethanolic extract (BLEE) at varying concentrations were electrospun on polylactic acid (PLA) films. Nanofibers with different morphologies, as indicated by scanning electron microscopy (SEM), were formed after solutions of gelatin/chitosan with and without BLEE were electrospun on PLA films at a constant voltage (25 kV) and a feed rate of 0.4 mL/h. Beaded gelatin/chitosan nanofibers (GC/NF) were found, particularly when high concentrations of BLEE were encapsulated. PLA films coated with GC/NF, and with BLEE added, showed antioxidant and antibacterial activities, which were augmented by increasing BLEE concentrations. Lower water vapor permeability and enhanced mechanical properties were achieved for GC/NF-coated PLA film (p < 0.05). Microbial growth and lipid oxidation of Nile tilapia slices packaged in PLA film coated with GC/NF containing 2% BLEE were more retarded than those packaged in low-density polyethylene (LDPE) bags over refrigerated storage of 12 days. Based on microbial limits, the shelf-life was escalated to 9 days, while the control had a shelf-life of 3 days. Therefore, such a novel film/bag could be a promising active packaging for foods.

The Molecular Weaponry Produced by the Bacterium Hafnia alvei in Foods

Hafnia alvei is receiving increasing attention from both a medical and veterinary point of view, but the diversity of molecules it produces has made the interest in this bacterium extend to the field of probiotics, the microbiota, and above all, to its presence and action on consumer foods. The production of Acyl Homoserine Lactones (AHLs), a type of quorum-sensing (QS) signaling molecule, is the most often-studied chemical signaling molecule in Gram-negative bacteria. H. alvei can use this communication mechanism to promote the expression of certain enzymatic activities in fermented foods, where this bacterium is frequently present. H. alvei also produces a series of molecules involved in the modification of the organoleptic properties of different products, especially cheeses, where it shares space with other microorganisms. Although some strains of this species are implicated in infections in humans, many produce antibacterial compounds, such as bacteriocins, that inhibit the growth of true pathogens, so the characterization of these molecules could be very interesting from the point of view of clinical medicine and the food industry. Lastly, in some cases, H. alvei is responsible for the production of biogenic amines or other compounds of special interest in food health. In this article, we will review the most interesting molecules that produce the H. alvei strains and will discuss some of their properties, both from the point of view of their biological activity on other microorganisms and the properties of different food matrices in which this bacterium usually thrives.

Betel (Piper betle L.) leaf ethanolic extracts dechlorophyllized using different methods: antioxidant and antibacterial activities, and application for shelf-life extension of Nile tilapia (Oreochromis niloticus) fillets

Different methods for chlorophyll removal were used for betel leaf ethanolic extracts (BLEE). Chlorophyll content, color, and antioxidant and antibacterial activities of the resulting extracts were examined. Sedimentation process remarkably reduced the chlorophyll content and color of BLEE (p < 0.05), while antioxidant and antibacterial activities were enhanced (p < 0.05). Polyphenol content and bioactivities of the extracts dechlorophyllized using organic solvents varied (p < 0.05). Antibacterial efficacy of BLEE dechlorophyllized by the sedimentation method (BLEE-SED) depended on concentrations. Lower minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of BLEE-SED toward 4 bacteria were obtained, compared to other extracts. Lower microbiological and chemical changes were achieved when Nile tilapia fillets were treated with BLEE-SED at 400 and 600 ppm after 12 days of storage at 4 °C. Therefore, sedimentation as a green process could be adopted for preparing a safe BLEE with augmented bioactivities and pale color, which could extend shelf-life of refrigerated Nile tilapia fillets.

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.

Histamine-Producing Bacteria and Histamine Induction in Retail Sardine and Mackerel from Fish Markets in Egypt

This study examined the occurrence of histamine-producing bacteria (HPB) and histamine induction in retail sardine and mackerel in Egypt; and whether the fish vendors play a role in the transmission of HPB. Fish were collected from the fish markets, additionally; hand swab samples were taken from the fish vendors. All samples were cultured on modified Niven's medium (MNM); the positive colonies were subcultured on Violet Red Bile Glucose (VRBG) agar, followed by biochemical identification and histidine decarboxylase (hdc)-gene-PCR of the VRBG-positive isolates. The hdc-gene-positive fish and human isolates were subjected to partial hdc-gene-sequencing and phylogenetic analysis. Production of histamine in the fish muscles was measured by high-performance liquid chromatography. A higher percentage of sardine showed the presence of MNM-positive bacteria (84%) than mackerel (53%). Enterobacteriaceae was the dominant family; the most frequent species were Enterobacter cloacae, Raoultella planticola, Citrobacter freundii, and Enterobacter aerogenes. Higher proportion of the R. planticola isolates were hdc positive as compared with the other species. Only 32% sardine and 17% mackerel of the MNM-positive isolates carried the hdc gene. Fish muscles that contain hdc-positive bacteria exhibit higher levels of histamine (median 86; IQR 80-1112 mg/kg) than those with hdc-negative bacteria (48; 75-223 mg/kg). The level of histamine was significantly higher in sardine (109; 104-1094 mg/kg) than in mackerel (40; 49-106 mg/kg). The 20 fish vendor samples were MNM positive, 2 of them were hdc-gene positive. The close genetic relatedness between the human and fish strains isolated from the same markets suggests a possible bidirectional transmission of the HPB. This warns for the presence of HPB carrying hdc gene in retail sardine and mackerel, which is associated with a relatively high level of histamine. Regular inspection of the fish markets is required, including accurate determination of HPB by using a combination of the MNM culture, hdc-gene PCR, and measurement of histamine level.