Influence of starter and nonstarter on the formation of biogenic amine in goat cheese during ripening

A Comprehensive Review on the Biogenic Amines in Cheeses: Their Origin, Chemical Characteristics, Hazard and Reduction Strategies

Most of the biogenic amines are naturally found in fermented foods as a consequence of amino acid decarboxylation. Their formation is ascribable to microorganisms (starters, contaminants and autochthonous) present in the food matrix. The concentration of these molecules is important for food security reasons, as they are involved in food poisoning illnesses. The most frequent amines found in foods are histamine, putrescine, cadaverine, tyramine, tryptamine, phenylethylamine, spermine and spermidine. One of the most risk-prone foods are cheeses, mostly ripened ones, which could easily accumulate amines due to their peculiar manufacturing process and ripening. Cheeses represent a pivotal food in our diet, providing for nutrients such as amino acids, calcium, vitamins and others; thus, since they are widely consumed, it is important to evaluate the presence of toxic molecules to avoid consumers' poisoning. This review aimed to gather general information on the role of biogenic amines, their formation, the health issues and the microorganisms and processes that produce/reduce them, with a focus on their content in different types of cheese (from soft to hard cheeses) and the biotic and abiotic factors that influence their formation or reduction and concentration. Finally, a multivariate analysis was performed on the biogenic amine content, derived from data available in the literature, to obtain more information about the factors influencing their presence in cheeses.

Unveiling the Potential of Lactic Acid Bacteria from Serbian Goat Cheese

This study aimed to unleash the potential of indigenous lactic acid bacteria (LAB) originating from traditionally made Serbian goat cheese. Following the isolation and identification of the LAB, the safety aspects of the isolates were evaluated through tests for hemolytic activity and antibiotic sensitivity. The selected isolates were then tested for various technological properties, including growth in methylene blue, proteolytic activity, acidification, curd formation ability in both pure and enriched goat milk, diacetyl production, antagonistic potential against other LAB, and biofilm formation ability. The results indicated that Lactococcus spp., Lacticaseibacillus spp., and Lactiplantibacillus spp. did not exhibit α or β hemolysis, while enterococci displayed α hemolysis. A higher number of isolates demonstrated sensitivity to ampicillin, tetracycline, and streptomycin, while sensitivity to gentamicin and vancomycin was strain-dependent. Based on the evaluation of technological properties, Lacticaseibacillus paracasei M-1 and Lactiplantibacillus plantarum C7-7, C7-8, and C14-5 showed promising characteristics. Additionally, Lactococcus lactis subsp. lactis strains C0-14 and C21-8 emerged as promising candidates with notable technological properties. Notably, certain indigenous strains LAB exhibit promising technological properties and safety profiles. These characteristics make them suitable candidates for use as starter or adjunct cultures in goat's milk cheese production, potentially enhancing the quality and safety of the cheese as well as hygiene practices among small-scale dairy producers.

Combination of SPE and fluorescent detection of AQC-derivatives for the determination at sub-mg/L levels of biogenic amines in dairy products

Biogenic amines (BAs) are compounds generated by decarboxylation of their amino acid precursors. Their intake, even at low concentrations, can lead to several types of health problems in sensitive individuals. As they can be easily formed in fermented dairy products, their quantitative determination is very relevant. In the present paper, a method for the quantitative determination of four biogenic amines in different dairy products has been developed, validated and applied to 37 samples of milk, 23 of yogurt, and 14 of kefir. Amines were selectively extracted using solid phase extraction, subsequently derivatizatized with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate and further determined by High Performance Liquid Chromatography with fluorescence detection. The method's sensitivity was highly satisfactory, with limits of detection lower than 0.2 mg/L. Optimal linearity and repeatability were also achieved. BAs were not detected in most of the milk samples, but they were found frequently at high levels in yogurt and kefir samples, reaching values of up to 79 mg/kg total BAs in kefir samples. Levels measured should not be a cause for concern for the population at large, but should be known by BAs-sensitive individuals.

Effect of forage type, season, and ripening time on selected quality properties of sheep milk cheese

The aim of this research was to study changes in the microbial populations, free AA profile, biogenic amine content, and sensory characteristics of ripened cheeses (100 and 180 d) produced in different seasons (summer, autumn, winter, and spring) from pasteurized sheep milk from 8 commercial flocks fed hay or silage diets. Twenty-one individual AA and 6 biogenic amines were determined by ultra-high performance liquid chromatography. Type of conserved forage for sheep feeding did not affect the variables studied, which is of great interest because hay and silage are low-cost ingredients for sheep feeding. Proteolysis led total free AA concentrations ranging between 35,179.26 and 138,063.71 mg/kg of cheese at 180 d of ripening. γ-Aminobutyric acid, which has been associated with beneficial effects on human health, was the second most abundant AA in all cheese samples, accounting for 15% of total free AA. Spring cheeses showed 2-fold higher concentrations of γ-aminobutyric acid than summer and autumn cheeses at the end of ripening. Overall, spring, winter, and autumn cheeses had lower average concentration of biogenic amines (431.99 mg/kg of cheese) than summer cheeses (825.70 mg/kg of cheese) as well as better sensory characteristics. Therefore, this study could provide the dairy industry with useful information for producing cheeses with valuable nutritional and sensory quality for consumers.

Detection of Biogenic Amines and Tyramine-Producing Bacteria in Fermented Sausages from Switzerland

ABSTRACT

Fermented foods can cause human illness because of the unhealthy effect of biogenic amines (BAs) that accumulate by decarboxylation of free amino acids. Salami-type fermented sausages can contain BAs, but which bacteria and environmental factors contribute to BA production is not clear. Sixty-two sausages purchased from Swiss markets were evaluated for decarboxylating bacterial strains and concentrations of the BAs cadaverine, histamine, putrescine, and tyramine. Based on the size and number of employees of the meat processing plants, sausages were separated into two groups: artisanal and industrial. Concentrations of all four BAs were higher in industrial sausages than in artisanal sausages. Tyramine was the major BA detected in 46 of 62 sausages, at a maximum concentration of 785.22 mg/kg. Enterococci and coagulase-negative staphylococci (mainly the meat starter culture Staphylococcus xylosus) were the main tyramine producers. Putrescine was found in 20 of 62 samples, at a maximum concentration of 707.77 mg/kg. Concentrations of these two BAs were significantly correlated (P = 0.0407). Cadaverine and histamine were detected in nine and eight samples, respectively, and both were found in significantly higher concentrations (P = 0.019 and 0.036, respectively) in industrial sausages. Based on the tyramine concentration, five groups of fermented sausages were identified: group 1, very high concentrations (>700 mg/kg); group 2, high concentrations (400 to 700 mg/kg); group 3, moderate concentrations (200 to 400 mg/kg); group 4, low concentrations (<200 mg/kg); group 5, concentrations below the detection limit (0.05 mg/kg). Product samples with tyramine concentrations >200 mg/kg were considered of lower quality because consumption of such samples could be unhealthy for sensitive consumers.

HIGHLIGHTS

Biogenic amines formation and their importance in fermented foods

Biogenic amines (BAs) are low molecular weight organic bases with an aliphatic, aromatic, or heterocyclic structure which have been found in many foods. biogenic amines have been related with several outbreaks of food-borne intoxication and are very important in public health concern because of their potential toxic effects. The accumulation of biogenic amines in foods is mainly due to the presence of bacteria able to decarboxylate certain amino acids. Biogenic amines are formed when the alpha carboxvl group breaks away from free amino acid precursors. They are colled after the amino acid they originated from. The main biogenic amines producers in foods are Gram positive bacteria and cheese is among the most commonly implicated foods associated with biogenic amines poisoning. The consumption of foods containing high concentrations of biogenic amines has been associated with health hazards and they are used as a quality indicator that shows the degree of spoilage, use of non-hygienic raw material and poor manufacturing practice. Biogenic amines may also be considered as carcinogens because they are able to react with nitrites to form potentially carcinogenic nitrosamines. Generally, biogenic amines in foods can be controlled by strict use of good hygiene in both raw material and manufacturing environments with corresponding inhibition of spoiling microorganisms. The aim of this review was to give some information about biogenic amines in foods.

Biogenic Amines in Traditional Fiore Sardo PDO Sheep Cheese: Assessment, Validation and Application of an RP-HPLC-DAD-UV Method

This contribution aimed to measure for the first time the amount of biogenic amines (BAs) in one of the most ancient and traditional sheep cheese produced in Sardinia, Italy: the Protected Designation of Origin (PDO) Fiore Sardo. To achieve this, an original RP-HPLC-DAD-UV method has been developed that was completely validated in terms of LoD, LoQ, linearity, precision and trueness, and tested on 36 real Fiore Sardo PDO cheese samples produced by four different cheesemakers and marketed by four stores. The average total concentration of the eight BAs (i.e., tyramine, tryptamine, histidine, putrescine, cadaverine, 2-phenylethylamine, spermine and spermidine) measured in Fiore Sardo cheese was 700 mg/kg, with a range between 170 mg/kg and 1,100 mg/kg. A great variability in the total amount of BAs has been evidenced among the Fiore Sardo marketed in the four stores as well as for the cheeses purchased in different times in the same store. Tyramine (350 mg/kg), putrescine (150 mg/kg), histamine (80 mg/kg) and cadaverine (30 mg/kg) are the most abundant BAs found in this matrix. Among the many factors concurring, the dominant microflora of Fiore Sardo PDO is likely the principal cause of the qualitative and quantitative distribution of BAs in this matrix. Finally, the total amount of BAs found in Fiore Sardo PDO is not able to cause any health alert situation for consumers.

Screening Method to Evaluate Amino Acid-Decarboxylase Activity of Bacteria Present in Spanish Artisanal Ripened Cheeses

A qualitative microplate screening method, using both low nitrogen (LND) and low glucose (LGD) decarboxylase broths, was used to evaluate the biogenic amine (BA) forming capacity of bacteria present in two types of Spanish ripened cheeses, some of them treated by high hydrostatic pressure. BA formation in decarboxylase broths was later confirmed by High Performance Liquid Chromatography (HPLC). An optimal cut off between 10⁻25 mg/L with a sensitivity of 84% and a specificity of 92% was obtained when detecting putrescine (PU), tyramine (TY) and cadaverine (CA) formation capability, although these broths showed less capacity detecting histamine forming bacteria. TY forming bacteria were the most frequent among the isolated BA forming strains showing a strong production capability (exceeding 100 mg/L), followed by CA and PU formers. Lactococcus, Lactobacillus, Enterococcus and Leuconostoc groups were found as the main TY producers, and some strains were also able to produce diamines at a level above 100 mg/L, and probably ruled the BA formation during ripening. Enterobacteriaceae and Staphylococcus spp., as well as some Bacillus spp. were also identified among the BA forming bacteria isolated.

Biogenic Amines in Dairy Products: Origin, Incidence, and Control Means

Biogenic amines (BAs) are toxic compounds produced by a number of microorganisms (bacteria, yeasts, and molds) as a result of the metabolism of some amino acid, usually decarboxylation reactions. BA-producing microorganisms are not necessarily pathogenic, such as lactic acid bacteria, which are, on the contrary, among the most beneficial microbiota to human beings and some of which even have probiotic properties. However, the incidence of BAs in dairy products and their possible implication in serious dairy-borne intoxications has long been overlooked. Consequently, the implementation of control measures to limit such an incidence has not been considered among the priorities of the food safety authorities. Nonetheless, there is a growing concern with regard to the presence of BAs in dairy products, because their toxicological status as toxins that may have serious acute and/or chronic adverse health effects is becoming increasingly evident and well-documented. The main BAs associated with dairy products are reviewed herein from the perspective of their incidence in these food products, and to draw the attention of readers to the shortage in data to perform pertinent risk assessment, which is considered to be a key action to provide efficient control means and to help decision makers issue appropriate legislative and regulatory measures.

Biogenic amines in Zamorano cheese: factors involved in their accumulation

BACKGROUND

Ripened cheese is among fermented food the most often associated with food poisoning from biogenic amines. The influence of ripening time, heat treatment of milk and the effect of using milk from a different ewe breed on the biogenic amine (BA) content of Zamorano cheese was studied by high-performance liquid chromatography. Physicochemical, proteolytic and microbiological parameters were also studied.

RESULTS

BA content increased significantly during ripening and their final values were around 400 mg kg(-1). Cheeses elaborated with raw milk duplicated the concentration of BA relative to those elaborated with pasteurized milk (72 °C for 20 s). The average levels of putrescine, spermine and tyramine were higher in cheeses made with a greater proportion of milk from Churra breed. Significant differences in microbial counts and nitrogen soluble in 5% phosphotungstic acid were observed between the different batches.

CONCLUSION

Ripening time and heat treatment applied to milk were the factors that exercised the greatest influence upon the concentration of BA in Zamorano cheese.

The evaluation of Zataria multiflora Boiss. essential oil effect on biogenic amines formation and microbiological profile in Gouda cheese

The effect of Zataria multiflora Boiss. (Z. multiflora) essential oils (EO) on biogenic amines (BAs) production and microbial counts in Gouda cheese has been investigated. Zataria multiflora was added to milk in different concentrations (0·05, 0·1, 0·2 and 0·4% (v/v)). The BAs (tyramine and histamine) were measured by RP-HPLC, following extraction from the cheese. Various microbiological analyses (aerobic mesophilic bacteria, enterococci, mesophilic lactobacilli, Enterobacteriaceae, lactococci and yeasts) were performed during ripening using the viable plate count method on specific culture media. The overall acceptability of cheeses was investigated by seven panellists. All the samples containing different concentrations of EO were acceptable to the panellists. Also, Gouda cheeses with 0·2% Z. multiflora EO showed the highest acceptability among all the samples. At the end of maturation period, 0·1, 0·2 and 0·4% Z. multiflora EO reduced tyramine and histamine significantly to 5%, 22% and 44% for tyramine and 14%, 29% and 46% for histamine, respectively, when compared to the control group. The increase of Z. multiflora EO concentrations led to further decrease in BAs content and microbial counts. The maximum microbiological reduction was observed in yeasts, and minimum microbiological reduction was seen in Enterobacteriaceae counts. Zataria multiflora EO could be used for reduction of BAs and also as a flavouring agent in Gouda cheese and could contribute to consumers' health.

SIGNIFICANCE AND IMPACT OF THE STUDY

The presence of biogenic amines in cheese has a serious impact on public health. Besides, there is growing concern about the use of chemical preservatives and the food industry is looking for new natural preservation methods. Zataria multiflora Boiss. essential oil is well known for its antimicrobial effects, and we attempted to reduce biogenic amines formation in Gouda cheese using Z. multiflora Boiss. essential oil as a natural additive. Furthermore, the desirable organoleptic qualities such as flavour, odour, texture and colour were achieved by adding Z. multiflora Boiss. to cheese.

Control of tyramine and histamine accumulation by lactic acid bacteria using bacteriocin forming lactococci

The aim of this study was to evaluate the competitive effects of three bacteriocin producing strains of Lactococcus lactis subsp. lactis against two aminobiogenic lactic acid bacteria, i.e. the tyramine producing strain Enterococcus faecalis EF37 and the histamine producing strain Streptococcus thermophilus PRI60, inoculated at different initial concentrations (from 2 to 6 log cfu/ml). The results showed that the three L. lactis subsp. lactis strains were able to produce bacteriocins: in particular, L. lactis subsp. lactis VR84 and EG46 produced, respectively, nisin Z and lacticin 481, while for the strains CG27 the bacteriocin has not been yet identified, even if its peptidic nature has been demonstrated. The co-culture of E. faecalis EF37 in combination with lactococci significantly reduced the growth potential of this aminobiogenic strain, both in terms of growth rate and maximum cell concentration, depending on the initial inoculum level of E. faecalis. Tyramine accumulation was strongly reduced when E. faecalis EF37 was inoculated at 2 log cfu/ml and, to a lesser extent, at 3 log cfu/ml, as a result of a lower cell load of the aminobiogenic strain. All the lactococci were more efficient in inhibiting streptococci in comparison with E. faecalis EF37; in particular, L. lactis subsp. lactis VR84 induced the death of S. thermophilus PRI60 and allowed the detection of histamine traces only at higher streptococci inoculum levels (5-6 log cfu/ml). The other two lactococcal strains did not show a lethal action against S. thermophilus PRI60, but were able to reduce its growth extent and histamine accumulation, even if L. lactis subsp. lactis EG46 was less effective when the initial streptococci concentration was 5 and 6 log cfu/ml. This preliminary study has clarified some aspects regarding the ratio between bacteriocinogenic strains and aminobiogenic strains with respect to the possibility to accumulate BA and has also showed that different bacteriocins can have different effects on BA production on the same strain. This knowledge is essentially aimed to use bacteriocinogenic lactococci as a predictable strategy against aminobiogenic bacteria present in cheese or other fermented foods.

Safety of a probiotic cheese containing Lactobacillus plantarum Tensia according to a variety of health indices in different age groups

Safety of the probiotic Lactobacillus plantarum strain Tensia (DSM 21380) was tested in vitro, in semihard Edam-type cheese, in an animal model and after consumption of the probiotic cheese in double-blind randomized placebo-controlled human intervention studies with different age groups. The susceptibility of L. plantarum Tensia to 8 antibiotics, and the presence of tetracycline (tet M, S, O, K, L) genes and class 1 integron was assessed by applying epsilometer-test and PCR-based methods. Production of biogenic amines by the probiotic strain in decarboxylation medium containing 1% of l-histidine, l-glutamine, l-ornithine, l-arginine, or l-lysine and in cheese was tested by gas chromatography. The biosafety of L. plantarum Tensia was evaluated on National Institutes of Health-line mice fed cheese containing Tensia at a concentration of 9.6 log cfu/g for 30 consecutive days. In human intervention trials in adults and the elderly, the effects of different doses of Edam-type cheese and the probiotic bacterium on BW, gut functionality indices, and host metabolism were evaluated. The strain L. plantarum Tensia was susceptible to all tested antibiotics and did not possess the tetracycline resistance-determining genes tet(L), tet(S) and tet(O), nor did it contain the integron (Int1) gene. However, the strain was tet(K) and tet(M) positive. Lactobacillus plantarum Tensia did not produce potentially harmful biogenic amines, such as histamine or cadaverine. The amount of tyramine produced in the cheese environment during ripening and after 15 wk of storage was below the clinically significant content. In the animal model, no translocation of the administered strain or other microbes into the blood or organs of mice was detected. No harmful effect was observed on body mass index, inflammatory markers, or serum lipidograms during human intervention trials with different age groups at a daily dose of 10.3 or 8.17 log cfu/serving for 3 wk. No negative effect on gastrointestinal welfare was observed, but the consumption of 100g/d for 3 wk caused hard stools from the second week of the trial. The content of total lactobacilli increased in feces, and the presence of the ingested probiotic strain was confirmed after the consumption of cheese. Thus, L. plantarum strain Tensia is suitable for generally recognized as safe (GRAS) and qualified presumption of safety (QPS) criteria because it did not have any undesirable characteristics. The regular semihard Edam-type cheese (fat content of 26%) with the probiotic additive at a daily dose of 50 g or in excess (100g) and with a probiotic daily dose of 10 log cfu for 3 wk was safe.

Focused review: agmatine in fermented foods

Polyamines (PAs) are ubiquitous substances considered to be bioregulators of numerous cell functions; they take part in cell growth, division, and differentiation. These biogenic amines are also involved in tissue repair and in intracellular signaling; in fact, because of their polycationic character, they interact to a large extent with membrane phospholipids and may play an important role in the regulation of membrane-linked enzymes. The intracellular polyamine content derives from the simultaneous regulation of the synthesis, catabolism, uptake, and elimination of the polyamines; furthermore, PAs are present in all cell types at different concentrations, but the highest levels are found in rapid-turnover tissues. In addition to spermidine, spermine, and putrescine, also agmatine (AGM), deriving from arginine and identified in mammals in the 1990s, is a polyamine and several studies have reported its potentially positive role in the production of secretagogues, and in neuronal, vascular, metabolic, and therapeutic functions. Because of the low arginine decarboxylase (ADC) activity in mammalians, the amounts of AGM found in their tissues can be only minimally ascribed to an endogenous de novo synthesis by ADC, while a substantial quantity of AGM may be of dietary origin. Several food products contain only small amounts of polyamines, while higher concentrations can be found in fermented foods. PAs could also be considered as indicators of freshness in fish and meat products; as these moieties are produced during food storage, it would seem to confirm the main role of microorganisms in their synthesis. In particular, high levels of AGM are present in alcoholic beverages, such as wine, beer, sake, which would seem to confirm the role of yeasts in AGM production. Although many biological functions have been attributed to polyamines, high levels of these compounds in foodstuffs can have toxicological effects; however, no safe level for the intake of polyamines in a diet has yet been established. In this paper the presence of AGM in different foodstuffs is discussed, also taking into account the various factors affecting its presence and concentration.

Factors influencing biogenic amines accumulation in dairy products

Fermented foods are among the food products more often complained of having caused episodes of biogenic amines (BA) poisoning. Concerning milk-based fermented foods, cheese is the main product likely to contain potentially harmful levels of BA, specially tyramine, histamine, and putrescine. Prompted by the increasing awareness of the risks related to dietary uptake of high biogenic amine loads, in this review we report all those elaboration and processing technological aspects affecting BA biosynthesis and accumulation in dairy foods. Improved knowledge of the factors involved in the synthesis and accumulation of BA should lead to a reduction in their incidence in milk products. Synthesis of BA is possible only when three conditions converge: (i) availability of the substrate amino acids; (ii) presence of microorganisms with the appropriate catabolic pathway activated; and (iii) environmental conditions favorable to the decarboxylation activity. These conditions depend on several factors such as milk treatment (pasteurization), use of starter cultures, NaCl concentration, time, and temperature of ripening and preservation, pH, temperature, or post-ripening technological processes, which will be discussed in this chapter.

Antilisterial activity of nisin-like bacteriocin-producing Lactococcus lactis subsp. lactis isolated from traditional Sardinian dairy products

With the aim of selecting LAB strains with antilisterial activity to be used as protective cultures to enhance the safety of dairy products, the antimicrobial properties of 117 Lactococcus lactis subsp. lactis isolated from artisanal Sardinian dairy products were evaluated, and six strains were found to produce bacteriocin-like substances. The capacity of these strains to antagonize Listeria monocytogenes during cocultivation in skimmed milk was evaluated, showing a reduction of L. monocytogenes counts of approximately 4 log units compared to the positive control after 24 h of incubation. In order for a strain to be used as bioprotective culture, it should be carefully evaluated for the presence of virulence factors, to determine what potential risks might be involved in its use. None of the strains tested was found to produce biogenic amines or to possess haemolytic activity. In addition, all strains were sensitive to clinically important antibiotics such as ampicillin, tetracycline, and vancomycin. Our results suggest that these bac+ strains could be potentially applied in cheese manufacturing to control the growth of L. monocytogenes.

Sequencing and transcriptional analysis of the biosynthesis gene cluster of putrescine-producing Lactococcus lactis

Lactococcus lactis is a prokaryotic microorganism with great importance as a culture starter and has become the model species among the lactic acid bacteria. The long and safe history of use of L. lactis in dairy fermentations has resulted in the classification of this species as GRAS (General Regarded As Safe) or QPS (Qualified Presumption of Safety). However, our group has identified several strains of L. lactis subsp. lactis and L. lactis subsp. cremoris that are able to produce putrescine from agmatine via the agmatine deiminase (AGDI) pathway. Putrescine is a biogenic amine that confers undesirable flavor characteristics and may even have toxic effects. The AGDI cluster of L. lactis is composed of a putative regulatory gene, aguR, followed by the genes (aguB, aguD, aguA, and aguC) encoding the catabolic enzymes. These genes are transcribed as an operon that is induced in the presence of agmatine. In some strains, an insertion (IS) element interrupts the transcription of the cluster, which results in a non-putrescine-producing phenotype. Based on this knowledge, a PCR-based test was developed in order to differentiate nonproducing L. lactis strains from those with a functional AGDI cluster. The analysis of the AGDI cluster and their flanking regions revealed that the capacity to produce putrescine via the AGDI pathway could be a specific characteristic that was lost during the adaptation to the milk environment by a process of reductive genome evolution.

Quantitative analysis of histidine decarboxylase gene (hdcA) transcription and histamine production by Streptococcus thermophilus PRI60 under conditions relevant to cheese making

This study evaluated the influence of parameters relevant for cheese making on histamine formation by Streptococcus thermophilus. Strains possessing a histidine decarboxylase (hdcA) gene represented 6% of the dairy isolates screened. The most histaminogenic, S. thermophilus PRI60, exhibited in skim milk a high basal level of expression of hdcA, upregulation in the presence of free histidine and salt, and repression after thermization. HdcA activity persisted in cell extracts, indicating that histamine might accumulate after cell lysis in cheese.

Sequencing and transcriptional analysis of the Streptococcus thermophilus histamine biosynthesis gene cluster: factors that affect differential hdcA expression

Histamine, a toxic compound that is formed by the decarboxylation of histidine through the action of microbial decarboxylases, can accumulate in fermented food products. From a total of 69 Streptococcus thermophilus strains screened, two strains, CHCC1524 and CHCC6483, showed the capacity to produce histamine. The hdc clusters of S. thermophilus CHCC1524 and CHCC6483 were sequenced, and the factors that affect histamine biosynthesis and histidine-decarboxylating gene (hdcA) expression were studied. The hdc cluster began with the hdcA gene, was followed by a transporter (hdcP), and ended with the hdcB gene, which is of unknown function. The three genes were orientated in the same direction. The genetic organization of the hdc cluster showed a unique organization among the lactic acid bacterial group and resembled those of Staphylococcus and Clostridium species, thus indicating possible acquisition through a horizontal transfer mechanism. Transcriptional analysis of the hdc cluster revealed the existence of a polycistronic mRNA covering the three genes. The histidine-decarboxylating gene (hdcA) of S. thermophilus demonstrated maximum expression during the stationary growth phase, with high expression levels correlated with high histamine levels. Limited expression was evident during the lag and exponential growth phases. Low-temperature (4 degrees C) incubation of milk inoculated with a histamine-producing strain showed lower levels of histamine than did inoculated milk kept at 42 degrees C. This reduction was attributed to a reduction in the activity of the HdcA enzyme itself rather than a reduction in gene expression or the presence of a lower cell number.

Tryptamine induces tryptophanyl-tRNA synthetase-mediated neurodegeneration with neurofibrillary tangles in human cell and mouse models

The neuropathological hallmarks of Alzheimer's disease (AD) and other taupathies include neurofibrillary tangles and plaques. Despite the fact that only 2-10% of AD cases are associated with genetic mutations, no nontransgenic or metabolic models have been generated to date. The findings of tryptophanyl-tRNA synthetase (TrpRS) in plaques of the AD brain were reported recently by the authors. Here it is shown that expression of cytoplasmic-TrpRS is inversely correlated with neurofibrillary degeneration, whereas a nonionic detergent-insoluble presumably aggregated TrpRS is simultaneously accumulated in human cells treated by tryptamine, a metabolic tryptophan analog that acts as a competitive inhibitor of TrpRS. TrpRSN- terminal peptide self-assembles in double-helical fibrils in vitro. Herein, tryptamine causes neuropathy characterized by motor and behavioral deficits, hippocampal neuronal loss, neurofibrillary tangles, amyloidosis, and glucose decrease in mice. Tryptamine induced the formation of helical fibrillary tangles in both hippocampal neurons and glia. Taken together with the authors' previous findings of tryptamine-induced nephrotoxicity and filamentous tangle formation in kidney cells, the authors' data indicates a general role of tryptamine in cell degeneration and loss. It is concluded that tryptamine as a component of a normal diet can induce neurodegeneration at the concentrations, which might be consumed along with food. Tryptophan-dependent tRNAtrp aminoacylation catalyzed by TrpRS can be inhibited by its substrate tryptophan at physiological concentrations was demonstrated. These findings indicate that the dietary supplementation with tryptophan as a tryptamine competitor may not counteract the deleterious influence of tryptamine. The pivotal role of TrpRS in protecting against neurodegeneration is suggested, providing an insight into the pathogenesis and a possible treatment of neurodegenerative diseases.

Real-time polymerase chain reaction for quantitative detection of histamine-producing bacteria: use in cheese production

Biogenic amines are toxic substances that appear in foods and beverages as a result of AA decarboxylation. The enzyme histidine decarboxylase catalyzes the decarboxylation of histidine to histamine, the biogenic amine most frequently involved in food poisoning. The aim of the present work was to develop a real-time quantitative PCR assay for the direct detection and quantification of histamine-producing strains in milk and cheese. A set of primers was designed, based on the histidine decarboxylase gene sequence of different gram-positive bacteria. The results show the proposed procedure to be a rapid (total processing time < 2 h), specific and highly sensitive technique for detecting potential histamine-producing strains. Chromatographic methods (HPLC) verified the capacity of real-time quantitative PCR to correctly quantify histamine accumulation.

The biogenic amine tyramine modulates the adherence of Escherichia coli O157:H7 to intestinal mucosa

The environmental factors that influence the ability of Escherichia coli O157:H7 to attach to the intestinal mucosa are incompletely understood. In the present study, the ability of one of the most common biogenic amines present in food, tyramine, to influence the ability of E. coli O157:H7 to adhere to murine cecal mucosa was examined. Ex vivo full-thickness sheets of murine cecum were mounted in Ussing chambers, which preserved the enteric nervous system innervation of the luminal epithelia and thereby allowed us to achieve a closer approximation of bacterial adherence than would be encountered in vivo. After exposure of the luminal aspect of the cecum to tyramine, E. coli O157:H7 was added for 90 min. The cecal tissue was then removed and washed, and adhered E. coli O157:H7 was enumerated using a selective medium. Tyramine significantly increased E. coli O157:H7 adherence to cecal mucosa when compared to that of controls. The 50% effective concentration of tyramine was 92.6 microM. Specific adrenergic antagonists were then employed to examine whether the effect of tyramine was mediated through alpha- or beta-adrenergic receptors on the intestinal tissue. Pretreatment of tissues with either the alpha-adrenergic receptor antagonist phentolamine or the beta-adrenergic receptor antagonist propranolol prevented the action of tyramine. Measurement of active transepithelial ion transport and ionic permeability in the cecal sheets before and after the addition of tyramine and E. coli O157:H7 did not show any impairment of tissue viability or transepithelial conductance. Further, tyramine did not influence either the growth of E. coli O157:H7 or the expression of the intimin attachment factor. The present findings suggest that biogenic amines, such as tyramine, present within the food matrix influence host susceptibility to E. coli O157:H7 infection.

Comparison of biogenic amine profile in cheeses manufactured from fresh and stored (4 degrees C, 48 hours) raw goat's milk

In this study, the evolution of microbial counts, biogenic amine contents, and related parameters (pH, moisture, and proteolysis) in goat cheese made from fresh raw milk or raw milk stored for 48 h at 4 degrees C was examined. In both cases the milk was nonpasteurized. This study was designed to evaluate the effect of milk quality on the profile of biogenic amines in relation to the evolution of the microbial population during cheese making. Cheese made from raw milk stored for 48 h at 4 degrees C showed the highest microbial counts and biogenic amine levels. The storage of milk under refrigeration caused significant increases in the levels of some microbial and biogenic amines during ripening, but not initially. Tyramine was the main biogenic amine in the two cheeses tested, followed by cadaverine. However, the main differences in amine contents between batches were found for putrescine, histamine, and beta-phenylethylamine, whose levels were more than twofold higher in samples from raw milk refrigerated for 48 h than in samples from fresh milk.