Development of a real-time PCR method coupled with a selective pre-enrichment step for quantification of Morganella morganii and Morganella psychrotolerans in fish products

Composition of the Midgut Microbiota Structure of Haemaphysalis longicornis Tick Parasitizing Tiger and Deer

Haemaphysalis longicornis is a common tick species that carries several pathogens. There are few reports on the influence of different hosts on the structure of midgut microflora in H. longicornis. In this study, midgut contents of fully engorged female H. longicornis were collected from the surface of tiger (Panthera tigris) and deer (Dama dama). The bacterial genomic DNA of each sample was extracted, and the V3-V4 regions of the bacterial 16S rRNA were sequenced using the Illumina NovaSeq sequencing. The diversity of the bacterial community of the fully engorged female H. longicornis on the surface of tiger was higher than that of deer. In total, 8 phyla and 73 genera of bacteria annotations were detected in the two groups. At the phylum level, the bacterial phyla common to the two groups were Proteobacteria, Firmicutes, and Actinobacteriota. At the genus level, there were 20 common bacterial genera, among which the relative abundances of Coxiella, Morganella, Diplorickettsia, and Acinetobacter were high. The Morganella species was further identified to be Morganella morganii. The alpha diversity index indicated that the bacterial diversity of the tiger group was higher than that of the deer group. Bacteroidota, Patescibacteria, Desulfobacterota, Verrucomicrobiota, and Cyanobacteria were solely detected in the tiger group. A total of 52 bacterial genera were unique in the tiger group, while one bacterial genus was unique in the deer group. This study indicates that there are differences in the structure of the gut bacteria of the same tick species among different hosts. Further culture-based methods are needed to provide a more comprehensive understanding of the tick microbiota parasitizing different hosts.

Unveiling the gut bacteriome diversity and distribution in the national fish hilsa (Tenualosa ilisha) of Bangladesh

The field of fish microbiome research has rapidly been advancing, primarily focusing on farmed or laboratory fish species rather than natural or marine fish populations. This study sought to reveal the distinctive gut bacteriome composition and diversity within the anadromous fish species Tenualosa ilisha (hilsa), which holds the status of being the national fish of Bangladesh. We conducted an analysis on 15 gut samples obtained from 15 individual hilsa fishes collected from three primary habitats (e.g., freshwater = 5, brackish water = 5 and marine water = 5) in Bangladesh. The analysis utilized metagenomics based on 16S rRNA gene sequencing targeting the V3-V4 regions. Our comprehensive identification revealed a total of 258 operational taxonomic units (OTUs). The observed OTUs were represented by six phyla, nine classes, 19 orders, 26 families and 40 genera of bacteria. Our analysis unveiled considerable taxonomic differences among the habitats (freshwater, brackish water, and marine water) of hilsa fishes, as denoted by a higher level of shared microbiota (p = 0.007, Kruskal-Wallis test). Among the identified genera in the gut of hilsa fishes, including Vagococcus, Morganella, Enterobacter, Plesiomonas, Shigella, Clostridium, Klebsiella, Serratia, Aeromonas, Macrococcus, Staphylococcus, Proteus, and Hafnia, several are recognized as fish probiotics. Importantly, some bacterial genera such as Sinobaca, Synechococcus, Gemmata, Serinicoccus, Saccharopolyspora, and Paulinella identified in the gut of hilsa identified in this study have not been reported in any aquatic or marine fish species. Significantly, we observed that 67.50% (27/40) of bacterial genera were found to be common among hilsa fishes across all three habitats. Our findings offer compelling evidence for the presence of both exclusive and communal bacteriomes within the gut of hilsa fishes, exhibiting potential probiotic properties. These observations could be crucial for guiding future microbiome investigations in this economically significant fish species.

Morganella Morganii Infection in Hirudo Medicinalis (Iran): A Case Report

Simple Summary

Morganella morganii is a motile, non-spore-forming, rod-shaped facultative an-aerobic gram-negative bacterium found in the intestines of people, the oral cavity of animals, and the environment. Reptiles, guinea pigs, rabbits, jaguars, elephant seals, broiler chickens, piglets, and dolphins have all been documented to have M. morganii infection. Medicinal leeches are used in surgical and non-surgical manners. Treatment of long-term and chronic pain syndrome induced by degenerative diseases in a non-surgical method. For the first time in Iran, our investigation discovered M. morganii-infected Hirudo medicinalis. Infection with M. morganii caused a significant death and morbidity rate (70%) and severe clinical abnormalities.

Abstract

Medicinal leeches (Hirudo medicinalis) are used in surgical and non-surgical manners. Morganella morganii is an opportunistic and zoonotic pathogenic bacterium causing serious clinical complications. In this study, we isolated, discovered and characterized M. morganii-infected H. medicinalis. We detected and identified M. morganii in all inflamed and swollen Hirudo medicinalis samples. The 16S rRNA sequence of the isolates confirmed all strains of M. morganii. All strains were sensitive to Ceftriaxone, Ceftiofur, Danofloxacin, Ciprofloxacin, Enrofloxacin, Oxytetracycline, and Meropenem and were resistant to Erythromycin, Amoxicillin, Ampicillin, Cefazolin, Colistin, Penicillin G, and Lincomycin. This pathogenic bacterium is a zoonotic pathogen, and monitoring the prevalence rate of this bacteria is strongly necessary for leeches used in human medical treatment and care. Finally, all infected leeches were treated successfully in this case report study.

Effect of Non-thermal Atmospheric Plasma on Viability and Histamine-Producing Activity of Psychotrophic Bacteria in Mackerel Fillets

Non-thermal atmospheric plasma (NTAP) has gained attention as a decontamination and shelf-life extension technology. In this study its effect on psychrotrophic histamine-producing bacteria (HPB) and histamine formation in fish stored at 0–5°C was evaluated. Mackerel filets were artificially inoculated with Morganella psychrotolerans and Photobacterium phosphoreum and exposed to NTAP to evaluate its effect on their viability and the histidine decarboxylase (HDC) activity in broth cultures and the accumulation of histamine in fish samples, stored on melting ice or at fridge temperature (5°C). NTAP treatment was made under wet conditions for 30 min, using a dielectric barrier discharge (DBD) reactor. The voltage output was characterized by a peak-to-peak value of 13.8 kV (fundamental frequency around 12.7 KHz). This treatment resulted in a significant reduction of the number of M. psychrotolerans and P. phosphoreum (≈3 log cfu/cm²) on skin samples that have been prewashed with surfactant (SDS) or SDS and lactic acid. A marked reduction of their histamine-producing potential was also observed in HDC broth incubated at either 20 or 5°C. Lower accumulation of histamine was observed in NTAP-treated mackerel filets that have been inoculated with M. psychrotolerans or P. phosphoreum and pre-washed with either normal saline or SDS solution (0.05% w/v) and stored at 5°C for 10 days. Mean histamine level in treated and control groups for the samples inoculated with either M. psychrotolerans or P. phosphoreum (≈5 log cfu/g) varied from 7 to 32 and from 49 to 66 μg/g, respectively. No synergistic effect of SDS was observed in the challenge test on meat samples. Any detectable amount of histamine was produced in the meat samples held at melting ice temperature (0–2°C) for 7 days. The effects of NTAP on the quality properties of mackerel’s filets were negligible, whereas its effect on the psychrotrophic HPB might be useful when time and environmental conditions are challenging for the cool-keeping capacity throughout the transport/storage period.

Development of a qPCR for the detection and quantification of Salmonella spp. in sheep feces and tissues

Salmonella spp. are common causes of disease in intensive livestock production systems, and contamination of foodstuffs is of significant concern for public health. Therefore, the identification and quantification of Salmonella spp. is important for monitoring the level of fecal shedding or tissue colonization in infected animals and animal products. We developed and evaluated a quantitative PCR (qPCR) method on spiked sheep tissue and fecal samples for the detection and quantification of Salmonella spp. Without the use of a pre-enrichment step, the qPCR limit of detection (LOD) results for sheep fecal (4 × 10⁴-6 × 10³ cfu/g) and tissue (4 × 10⁵-4 × 10³ cfu/g) samples were not adequate for detection purposes. With the inclusion of a 6-h pre-enrichment step in buffered peptone water (BPW), the LOD was 9 cfu/g (2.57 × 10¹ copies/g) in sheep feces, and 5.4 cfu/g (3.22 copies/g) sheep tissue. Comparison of the 6-h BPW qPCR method with a 24-h mannitol-selenite-cystine broth enrichment culture method using spiked samples revealed a sensitivity of 91% and 92%, respectively, and a specificity of 100% for both methods. The correlation was significant between the quantity (copies/mL) of Salmonella spp. in BPW at 6 h and at 0 h, allowing semiquantitative analysis. Our results demonstrate that, following inclusion of a 6-h pre-enrichment step in BPW, qPCR is semiquantitative with improved LODs of Salmonella spp. in sheep fecal and tissue samples.

[Development of the Genus and Species Determination Method for Histamine Producing Bacteria Isolated from Fishery Product with High-Resolution Melting Analysis]

Histamine in foods with a high histidine content may be produced by bacteria with histidine decarboxylase activity. Consumption of food enriched in histamine can produce symptoms of histamine poisoning that include flushing, headache, and urticaria. The number of histamine poisoning cases in Japan has decreased with developments in food hygiene management technology. However, approximately 10 cases are still reported each year. In addition, there have been cases where histamine was detected in the end products, prompting large product recalls. To prevent and identify causes of histamine toxicity, manufacturers must identify the bacteria causing the illness. A simple method of identification is needed, since sequence-based identification is complicated to perform and the analysis takes a long time. High-Resolution Melting Analysis (HRMA) is a method that detects differences in the base sequences of PCR products manifested as varied melting temperatures of double-stranded DNA. The present study was intended to develop a rapid identification method for major histamine-producing bacteria using HRMA. Species-specific HRMA primers were designed that specifically targeted the hdcA gene of 20 Gram-negative histamine-producing bacterial strains. The designed primers were used for HRM analysis of the 20 histamine-producing bacterial strains. The strains were divided into three groups (A, B, and C) based on differences in melting temperature values obtained by T_m Calling analysis program. Group A comprised terrestrial bacteria, such as Morganella, Enterobacter, and Raoultella, while Groups B and C comprised marine bacteria, such as those belonging to the genera Vibrio and Photobacterium. The melting profiles obtained in Group A by HRMA were used to identify the aforementioned terrestrial bacteria. The findings indicated that HRMA can easily identify the major gram-negative histamine-producing bacteria. A flow chart was created to identify histamine-producing bacterial species. This method enables the identification of histamine-producing bacterial species more quickly and easily than conventional sequence-based methods. Therefore, the method could be valuable for food companies to screen raw materials and products and track the source of contamination, which will in turn contribute to the prevention of histamine-food poisoning and investigation of its causes.

Biosensing the Histamine Producing Potential of Bacteria in Tuna

Histamine poisoning is the most common cause of human foodborne illness due to the consumption of fish products. An enzyme-based amperometric biosensor was developed to be used as a screening tool to detect histamine and histamine-producing bacteria (HPB) in tuna. It was developed by immobilizing histidine decarboxylase and horseradish peroxidase on the surface of screen-printed electrodes through a cross-linking procedure employing glutaraldehyde and bovine serum albumin. The signal generated in presence of histamine at the surface of the electrode was measured by chronoamperometry at in presence of a soluble redox mediator. The sensitivity of the electrode was 1.31-1.59 μA/mM, with a linear range from 2 to 20 μg/ml and detection limit of 0.11 μg/ml. In this study fresh tuna filets purchased in supermarkets in different days (n = 8) were analyzed to detect HPB. Samples with different concentration of histamine were analyzed with culture-based counting methods, biosensor and HPLC and also a challenge test was made. Recovery of histamine from cultures and tuna samples was also assessed. The presence of Morganella psychrotolerans, Photobacterium phosphoreum, P. damselae and Hafnia alvei was detected using culture- and PCR-based methods. At the time of purchase these tuna samples had histamine concentrations from below the limit of detection (LOD) to 60 μg/g. HPLC and biosensor methods provided similar results in the range from zero to 432 μg/g (correlation coefficient, R 2 = 0.990) and the recovery of histamine from cultures and tuna samples was very high (mean bias -12.69 to 1.63%, with root-mean-square error <12%). These results clearly show that fresh tuna is commonly contaminated with strong HPB. The histamine biosensor can be used by the Food Business Operators as a screening tool to detect their presence and to determine whether their process controls are adequate or not.

Detection and Characterization of Histamine-Producing Strains of Photobacterium damselae subsp. damselae Isolated from Mullets

Photobacterium damselae subsp. damselae (Pdd) is considered to be an emerging pathogen of marine fish and has also been implicated in cases of histamine food poisoning. In this study, eight strains isolated from mullets of the genera Mugil and Liza captured in the Ligurian Sea were characterized, and a method to detect histamine-producing Pdd from fish samples was developed. The histamine-producing potential of the strains was evaluated in culture media (TSB+) using a histamine biosensor. Subsequently, two strains were used to contaminate mackerel fillets (4 or 40 CFU/g), simulating a cross-contamination on the selling fish stalls. Sample homogenates were enriched in TSB+. The cultures were then inoculated on thiosulfate-citrate-bile salts-sucrose agar (TCBS) and the dark green colonies were cultured on Niven agar. The violet isolates were characterized using specific biochemical and PCR based tests. All Pdd strains were histamine producers, yielding concentration varying from 167 and 8977 µg/mL in TSB+ cultures incubated at 30 °C for 24 h. Pdd colonies were detected from the inoculated mackerel samples and their histidine decarboxylase gene was amplified using species-specific primer pairs designed for this study. The results indicate that mullets can be source of Pdd and the fish retailers needs to evaluate the risk posed by cross-contamination on the selling fish stalls.

Changes in integrity of the gill during histidine deficiency or excess due to depression of cellular anti-oxidative ability, induction of apoptosis, inflammation and impair of cell-cell tight junctions related to Nrf2, TOR and NF-κB signaling in fish

This study firstly explored the possible effects of dietary histidine on structural integrity and the related signaling factor gene expression in the gills of fish. Young grass carp (Ctenopharyngodon idella) were fed with six diets containing gradual levels of histidine for 8 weeks. The results firstly demonstrated that histidine deficiency caused increases in reactive oxygen species (ROS) contents, and severe oxidative damage (lipid peroxidation and protein oxidation) in the gills of fish, which was partially due to the decreased glutathione (GSH) content and antioxidant enzyme activities [superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione-S-transferase (GST) and glutathione reductase (GR)]. Further investigations indicated that histidine deficiency caused depressions of those antioxidant enzyme activities are related to the down-regulation of corresponding antioxidant enzyme genes and the related signaling factor Nrf2 mRNA levels. Meanwhile, histidine deficiency induced DNA fragmentation via up-regulation of caspase-3, caspase-8 and caspase-9 expressions that referring to the down-regulation of TOR and S6K mRNA levels. Furthermore, His deficiency down-regulated claudin-b, claudin-c, claudin-3, claudin-12, claudin-15, occludin and ZO-1 transcription in fish gills. These effects were partially related to the up-regulation of pro-inflammatory cytokines, interleukin 1β (IL-1β), interleukin 8 (IL-8), tumor necrosis factor-α (TNF-α) and related signaling factor nuclear factor κB P65 (NF-κB P65) mRNA levels, and the down-regulation of anti-inflammatory cytokines, interleukin 10 (IL-10), transforming growth factor β1 (TGF-β1) and related signaling factor IκBα mRNA levels. Excessive histidine exhibited negative effects that were similar to histidine deficiency, whereas the optimal histidine levels reversed those negative effects. Taken together, our results showed that histidine deficiency or excess impaired the structural integrity of fish gill by disrupted fish antioxidant defenses and regulating the expression of tight junction protein, cytokines, apoptosis, antioxidant enzymes, NF-κB p65, IκBα, TOR, Nrf2, Keap1 and apoptosis-related genes in the fish gills.

Whole-cell-based identification of electrochemically active bacteria in microbial fuel cells by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

RATIONALE

Electrochemically active bacteria (EAB) that are capable of producing electricity from renewable biomass and organic wastes have been of particular interest in recent years. Methods for selective enrichment, accurate identification and easy acquisition of EAB fingerprints for phylogenetic characterization would facilitate utilization of these bioenergy-producing species in practical environmental engineering applications.

METHODS

Electricigens/exoelectrogens were selectively enriched from domestic wastewater in a microbial fuel cell (MFC). Whole EAB cell-derived mass spectra were obtained with simple agar incubation for 24 h and subsequent release of proteins by 25% formic acid (FA) and ultrasonication. Mass fingerprints of EAB were obtained by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/TOF-MS) and species-specific analyses were completed by using the Spectral ARchive and Microbial Identification System (SARAMIS).

RESULTS

EAB could be discriminated by clustering of MALDI-TOF/TOF-MS results. Different species in mixtures originating from domestic sewage could be identified unambiguously at 99.90% confidence. Five species, namely Klebsiella oxytoca (K. oxytoca), Comamonas testosterone (C. testosterone), Pseudomonas putida (P. putida), Klebsiella pneumonia (K. pneumonia) and Raoultella ornithinolytica (R. ornithinolytica), that are known to be of clinical significance, were found to be enriched in MFCs and determined as high power-producing species. By using an agglomerative clustering algorithm to compute spectral similarity and diversity, a dendrogram was constructed to illustrate the phylogenetic relationships for EAB on the basis of mass spectral analyses.

CONCLUSIONS

An integrated method based on MFC-enrichment, agar-cultivation and MALDI-TOF/TOF-MS identification of whole-cell-extracted proteins has been proved to be a simple, rapid and reliable approach for rapid identification and routine inspection of EAB. Mixed phyla can be analyzed at species level to provide phylogenetic information on the highly efficient bacteria generating electricity from domestic wastewater.