Foodborne Intoxication Research Articles

Antimicrobial activity of essential oils of Origanum vulgare L. and Origanum majorana L. against Staphylococcus aureus isolated from poultry meat

One of the microorganisms present in poultry meat products responsible for the most usual foodborne intoxication is Staphylococcus aureus. Essential oil of spices has been used as a bio-preservative due to its antimicrobial activity against foodborne pathogens. The aim of this study was to evaluate the antimicrobial activity in vitro of the essential oils of oregano and marjoram against S. aureus isolated from poultry meat marketed in Pelotas/RS—Brazil, and to carry out the phenotypic and molecular characterization of these oils. For this, twenty samples of poultry meat were analyzed. Staphylococcus spp. was isolated from Baird Parker agar, and its molecular characterization was performed by PCR. All isolates of S. aureus were tested for the presence of genes coding for staphylococcal enterotoxins. Antimicrobial activity of essential oils of oregano and marjoram was evaluated by disk diffusion, minimal inhibitory concentration and minimal bactericidal concentration. The results showed that seventeen samples were contaminated by Staphylococcus positive-coagulase and nine were positive to acriflavine resistance and thermonuclease tests, and in the last ones S. aureus was confirmed. The genes coding for staphylococcal enterotoxins detected were sea (6) and seb (3). All isolates were sensitive to essential oils tested, indicating that these can be an alternative to food preservation.

Evaluation of Potential Effects of NaCl and Sorbic Acid on Staphylococcal Enterotoxin A Formation.

The prophage-encoded staphylococcal enterotoxin A (SEA) is recognized as the main cause of staphylococcal food poisoning (SFP), a common foodborne intoxication disease, caused by Staphylococcus aureus. Studies on the production of SEA suggest that activation of the SOS response and subsequent prophage induction affect the regulation of the sea gene and the SEA produced, increasing the risk for SFP. The present study aims to evaluate the effect of NaCl and sorbic acid, in concentrations relevant to food production, on SOS response activation, prophage induction and SEA production. The impact of stress was initially evaluated on steady state cells for a homogenous cell response. NaCl 2% was found to activate the SOS response, i.e., recA expression, and trigger prophage induction, in a similar way as the phage-inducer mitomycin C. In contrast, sorbic acid decreased the pH of the culture to a level where prophage induction was probably suppressed, even when combined with NaCl stress. The impact of previous physiological state of the bacteria was also addressed on cells pre-exposed to NaCl, and was found to potentially affect cell response upon exposure to further stress. The results obtained highlight the possible SFP-related risks arising from the use of preservatives during food processing.

Determination of histamine in milkfish stick implicated in food-borne poisoning

An incident of food-borne poisoning causing illness in 37 victims due to ingestion of fried fish sticks occurred in September 2014, in Tainan city, southern Taiwan. Leftovers of the victims' fried fish sticks and 16 other raw fish stick samples from retail stores were collected and tested to determine the occurrence of histamine and histamine-forming bacteria. Two suspected fried fish samples contained 86.6 mg/100 g and 235.0 mg/100 g histamine; levels that are greater than the potential hazard action level (50 mg/100 g) in most illness cases. Given the allergy-like symptoms of the victims and the high histamine content in the suspected fried fish samples, this food-borne poisoning was strongly suspected to be caused by histamine intoxication. Moreover, the fish species of suspected samples was identified as milkfish (Chanos chanos), using polymerase chain reaction direct sequence analysis. In addition, four of the 16 commercial raw milkfish stick samples (25%) had histamine levels greater than the US Food & Drug Administration guideline of 5.0 mg/100 g for scombroid fish and/or products. Ten histamine-producing bacterial strains, capable of producing 373–1261 ppm of histamine in trypticase soy broth supplemented with 1.0% L-histidine, were identified as Enterobacter aerogenes (4 strains), Enterobacter cloacae (1 strain), Morganella morganii (2 strains), Serratia marcescens (1 strain), Hafnia alvei (1 strain), and Raoultella orithinolytica (1 strain), by 16S ribosomal DNA sequencing with polymerase chain reaction amplification.

Effect of post-slaughter time and storage conditions on chemical and microbial changes in locally marketed beef

Fresh meat is commonly marketing at environmental temperature for long time in many developing countries including Bangladesh. The present study was conducted to assess whether elapsed time between slaughter and preservation and storage conditions influence the chemical and microbial changes of locally marketed beef. Meat samples were collected from local markets and divided into two groups, morning and evening beef. Morning beef was collected immediately after slaughtering from healthy cattle while evening one was collected 8 h after slaughtering. The samples were kept either in refrigerator (4oC) or freezer (-20oC). Refrigerated samples were stored for 7 days and analyzed on day1st, 3rd and 7th while frozen samples were stored for 90 days and analyzed on day 3rd, 45th and 90th. Results showed that there was a significant difference in chemical and microbial parameters between morning and evening beef (p<0.01 to 0.05). With respect to the advances of storage time, the dry matter, crude protein, ether extract and ash contents were increased in beef sample (p<0.01), indicating the moisture loss from meat time elapsed after slaughtering. Moreover, the coliform, yeast and mold counts were also increased with advance of storage time (p<0.01 to0.05),indicating the unhygienic conditions of slaughter house, equipment and water which is giving signal for the possible occurrence of food borne intoxication. In conclusion, we found that the quality of marketed beef degraded with the time elapsed before storage and storage temperature suggesting the importance of early preservation of meat at lower temperature. Our findings of increased number of microbial counts were also suggested the necessity to improve the hygienic conditions of slaughterhouse and equipment in developing countries like Bangladesh.DOI: http://dx.doi.org/10.3329/bjas.v44i1.23143 Bang. J. Anim. Sci. 2014. 44 (1): 52-58

Further evidence for staphylococcal food poisoning outbreaks caused by egc-encoded enterotoxins.

Staphylococcal food poisoning represents the most prevalent foodborne intoxication worldwide. It is caused by oral intake of enterotoxins preformed by Staphylococcus aureus in food. The relevance of newly described enterotoxins in outbreaks of staphylococcal food poisoning is controversially discussed. Although the staphylococcal enterotoxins SEG, SEI, SEM, SEN, and SEO elicit emesis in a monkey feeding assay, there has been no conclusive proof of their emetic activity in humans. In this study, we provide further evidence suggesting that one of these enterotoxins or a combination of SEG, SEI, SEM, SEN, and SEO cause staphylococcal food poisoning. We investigated two outbreaks registered with the Swiss Federal Office of Public Health, in which only Staphylococcus aureus strains harboring the egc cluster, including seg, sei, sem, sen, and seo linked to typical signs of staphylococcal food poisoning were isolated. The outbreaks were caused by consumption of raw goat cheese and semi-hard goat cheese, and were linked to strains assigned to CC45 (agr type I) and CC9 (agr type II), respectively. These outbreaks provide further evidence that newly-described staphylococcal enterotoxins are likely to cause staphylococcal food poisoning in humans.

Chemodiversity of cereulide, the emetic toxin of Bacillus cereus.

Food-borne intoxications are increasingly caused by the dodecadepsipeptide cereulide, the emetic toxin produced by Bacillus cereus. As such intoxications pose a health risk to humans, a more detailed understanding on the chemodiversity of this toxin is mandatory for the reliable risk assessment of B. cereus toxins in foods. Mass spectrometric screening now shows a series of at least 18 cereulide variants, among which the previously unknown isocereulides A-G were determined for the first time by means of UPLC-TOF MS and ion-trap MS(n) sequencing, (13)C-labeling experiments, and post-hydrolytic dipeptide and enantioselective amino acid analysis. The data demonstrate a high microheterogeneity in cereulide and show evidence for a relaxed proof reading function of the non-ribosomal cereulide peptide synthetase complex giving rise to an enhanced cereulide chemodiversity. Most intriguingly, the isocereulides were found to differ widely in their cell toxicity correlating with their ionophoric properties (e.g., purified isocereulide A showed about 8-fold higher cytotoxicity than purified cereulide in the HEp-2 assay and induced an immediate breakdown of bilayer membranes). These findings provide a substantial contribution to the knowledge-based risk assessment of B. cereus toxins in foods, representing a still unsolved challenge in the field of food intoxications.

Prevalence and antibiotic resistance characteristics of Salmonella spp. isolated from food-producing animals and meat products in Korea

Salmonellosis is a significant public health concern and a major cause of bacterial foodborne poisoning in Korea. Approximately 95% of salmonellosis cases in humans are related to the intake of contaminated food products, which mostly originate from livestock such as poultry, pigs, and cattle. To successfully develop strategies to reduce the spread of Salmonella, it is important to investigate the prevalence of Salmonella spp. isolated from food animals and meat. In Korea, the prevalence of Salmonella spp. in cattle was 1.2 2.0%, whereas in pigs it was 1.5 21%. Of all livestock and meat products analyzed, the Salmonella isolation rate was the highest in chickens (18.8 30.3%) and their meat. Antibiotic resistance is an important social issue. The frequent use of antibiotics in the livestock industry has led to increased antibiotic resistance in Salmonella isolates that are extracted from livestock, which raises serious public health concerns. To prevent the spread of antibiotic resistance, it is essential to collect data related to antibiotic-resistant Salmonella strains isolated from food animals and meat. Antibiotic resistance tests revealed that Salmonella isolated from cattle, pigs, and poultry were highly resistant to tetracycline and streptomycin. Recent studies show that the overuse of antibiotics in food animals can also affect antibiotic resistance in humans. Therefore, it is important to establish an appropriate management strategy to successfully prevent misuse of antibiotics within the Korean livestock industry.

Assessment of human health risk associated with pyaemia in Danish finisher pigs when conducting visual-only inspection of the lungs

The most important lesion to be overlooked when performing visual-only inspection of the lungs is embolic pneumonia. The aim of the present study was to assess the additional human health risk represented by overlooking cases of pyaemia represented by embolic pneumonia in finisher pigs, when conducting visual-only compared to palpation of the lungs, as is the traditional meat inspection procedure.An examination of bacteria isolated from 19 finisher pigs identified with embolic pneumonia at traditional meat inspection was undertaken. From each pig samples were taken from various organs (lungs, spleen, heart, liver and kidney), from the carpal joints (A. carpi) and flexor muscle (M. flexor digitorum superficialis) on the right foreleg. These data were included in a risk assessment following OIE guidelines.Bacteria were isolated from 78 out of 127 tissue and swap samples taken (61% positive samples). Staphylococcus aureus (N=37) was the most frequently isolated bacterium. The predominant site of S. aureus was the lung. S. aureus was detected although less frequently in low numbers in some organs (<100CFU/sample) and muscle samples (<10CFU/sample). Only one MRSA isolate was found.Staphylococcus warneri (N=24) was the second most commonly found bacterium. There was no predominant site and the number of S. warneri was less than 50CFU per sample.The risk of a food-borne intoxication from S. aureus in relation to pyaemia in pigs was considered very low due to the low quantitative numbers of S. aureus in muscle tissue samples. Implementing visual-only inspection will reduce the exposure of S. aureus due to less cross-contamination and handling of the plucks by the meat inspectors. The human health risk associated with S. warneri was considered very low, due to the limited zoonotic potential of this bacterium. In conclusion, the additional human health risk in relation to possibly overlooking pyaemia in Danish finisher pigs was considered negligible when conducting visual-only compared to traditional meat inspection.

WITHDRAWN: Staphylococcus aureus and understanding the factors that impact enterotoxin production in foods: A review

The staphylococci and their enterotoxins (SEs) are probably the most common cause of foodborne intoxication. There are numerous attributes that allow the major pathogen Staphylococcus aureus to act as an effective foodborne pathogen. This review will focus on the present knowledge of SEs and their production; examples of staphylococcal food poisoning outbreaks; nutritional factors affecting SE production; and select S. aureus-factors and -mechanisms that might be required for growth in food matrices.

Virulence and Resistance Gene Profiles of Staphylococcus aureus Strains Isolated from Ready-to-Eat Foods

Staphylococcal food poisoning represents the most prevalent foodborne intoxication worldwide. Oral intake of staphylococcal enterotoxins from food can result in emesis and diarrhea and can be fatal in children and the elderly. Few data have been available on the characteristics and sources of Staphylococcus aureus strains isolated from ready-to-eat (RTE) foods. In this study, we used a DNA microarray to determine virulence and antimicrobial resistance gene profiles of S. aureus from RTE foods. A total of 267 S. aureus strains isolated from 244 RTE foods were investigated. The isolates originated from precooked foods (41% of isolates), meat and fish products (17%), cheese (13%), delicatessen salads (8%), sandwiches and canapés (8%), confectionery and bakery products (6%), and various other RTE foods (7%). Eleven samples (5%), of which 9 were raw milk cheeses, contained >105 CFU/g, which is considered a health risk. Four S. aureus strains were associated with intoxications; three cases were linked to consumption of cheese and one case was linked to consumption of potato salad. DNA microarray results revealed that one-third of the tested strains had at least one major enterotoxin gene (sea through see). We also detected the toxic shock syndrome gene (18% of isolates) and various genes conferring antimicrobial resistance, including genes involved in resistance to beta-lactams (blaZ, 72% of isolates), methicillin (mecA, 1% of isolates), and vancomycin (vanB, 1% of isolates). S. aureus strains were most frequently assigned to clonal complex (CC) 30 (17% of isolates), CC8 (12%), CC15 (11%), and CC45 (10%), which are commonly detected in humans colonized or infected with S. aureus. Although a large proportion of the tested food items contained milk, we did not detect CC705, the most prevalent clonal complex among S. aureus isolates from bovine mastitis milk. Our results suggest that S. aureus isolates from RTE foods do not commonly originate from animals but more likely come from food handlers who contaminate foods.

Validation of reference genes for normalization of qPCR mRNA expression levels in Staphylococcus aureus exposed to osmotic and lactic acid stress conditions encountered during food production and preservation.

Staphylococcus aureus represents the most prevalent cause of food-borne intoxications worldwide. While being repressed by competing bacteria in most matrices, this pathogen exhibits crucial competitive advantages during growth at high salt concentrations or low pH, conditions frequently encountered in food production and preservation. We aimed to identify reference genes that could be used to normalize qPCR mRNA expression levels during growth of S. aureus in food-related osmotic (NaCl) and acidic (lactic acid) stress adaptation models. Expression stability of nine housekeeping genes was evaluated in full (LB) and nutrient-deficient (CYGP w/o glucose) medium under conditions of osmotic (4.5% NaCl) and acidic stress (lactic acid, pH 6.0) after 2-h exposure. Among the set of candidate reference genes investigated, rplD, rpoB,gyrB, and rho were most stably expressed in LB and thus represent the most suitable reference genes for normalization of qPCR data in osmotic or lactic acid stress models in a rich medium. Under nutrient-deficient conditions, expression of rho and rpoB was highly stable across all tested conditions. The presented comprehensive data on changes in expression of various S. aureus housekeeping genes under conditions of osmotic and lactic acid stress facilitate selection of reference genes for qPCR-based stress response models.

Emetic Bacillus cereus are more volatile than thought: recent foodborne outbreaks and prevalence studies in Bavaria (2007-2013).

Several Bacillus cereus strains possess the genetic fittings to produce two different types of toxins, the heat-stable cereulide or different heat-labile proteins with enterotoxigenic potential. Unlike the diarrheal toxins, cereulide is (pre-)formed in food and can cause foodborne intoxications shortly after ingestion of contaminated food. Based on the widely self-limiting character of cereulide intoxications and rarely performed differential diagnostic in routine laboratories, the real incidence is largely unknown. Therefore, during a 7-year period about 4.300 food samples linked to foodborne illness with a preliminary report of vomiting as well as food analysed in the context of monitoring programs were investigated to determine the prevalence of emetic B. cereus in food environments. In addition, a lux-based real-time monitoring system was employed to assess the significance of the detection of emetic strains in different food matrices and to determine the actual risk of cereulide toxin production in different types of food. This comprehensive study showed that emetic strains are much more volatile than previously thought. Our survey highlights the importance and need of novel strategies to move from the currently taxonomic-driven diagnostic to more risk orientated diagnostics to improve food and consumer safety.

English

This study aimed to analyze the bacteriological profile of commercially prepared pork sold along commercial streets of Nkwen through Bambili in Cameroon. A total of 11 duplicate randomly collected pork samples were analyzed microbiologically for bacteria. All the pork meat samples analyzed confirmed the presence of bacterial pathogens, indicating the need for strict implementation of food sanitation practices to reduce the possible risk of transmission of infection on consumption of these prepared pork. The mean microbial load on the cooked pork meat ranged between 1.9 x 104 - 3.8 x 104 cfu/g and total coliform count between 1.1 x 103-3.0 x 103 cfu/g. The bacterial isolated includes: Staphyloccocus aureus (81.8%) which was the most predominant, followed by Klebsiella pneumoniae (72.7%), Escherichia coli (54.4%), Salmonella spp. (45.4%), Proteus vulgaris (27%) and Shigella spp. (9%). The presence of these organisms in cooked pork meat foods should receive particular attention, because their presence indicate public health hazard and give warning signal for the possible occurrence of food borne intoxication. Key words: Nkwen/Bambili, Escherichia coli, pork meat, total coliforms, bacteria.

Foodborne Infections and Intoxications

The global supply of food has led to an increasingly connected planet, not only in terms of food products but also in terms of risks for foodborne diseases. The fourth edition of Morris and Potter’s Foodborne Infections and Intoxications delivers an in-depth look at the global effects of foodborne illnesses, provides pathogen-specific information, and describes processes and policies intended to prevent these illnesses. The text is a well-written and well-referenced guide to foodborne illnesses, containing contributions from >70 experts in epidemiology and the basic sciences of foodborne diseases. The text has been organized into 6 sections. The first section describes the epidemiology of foodborne disease, highlighting the most common illnesses in the United States and abroad with country-specific data as well as the most common outbreak-associated foods and microbial risk assessment. The next 4 sections encompass microbe-specific illnesses; each section comprises chapters on specific pathogens. The sections are organized to include bacterial pathogens, viral pathogens, parasites (along with mycobacteria and prions), and agents involved with food intoxications. Each chapter is specific to a given pathogen and includes a clinical description of the disease, the microbiology of the pathogen, exposure risks, and disease prevention. Chapters have been written by leading researchers in their respective fields and are filled with up-to-date references on each pathogen. One example, in Chapter 8, includes a description of the 2011 outbreak of Escherichia coli O104:H4 infections in northern Germany. This outbreak illustrates the importance of food safety and the critical role of public health officials, clinicians, and scientists in identifying new outbreaks and limiting the spread of newly identified illnesses. The final section of the book outlines prevention of foodborne diseases and discusses food safety and the legal basis for food safety regulation. This edition of Foodborne Infections and Intoxications updates the third edition, published in 2006, with increased emphasis on global disease prevention and a risk-based approach to food safety. This text is particularly valuable for students and practitioners in the fields of public health and food safety. It can also serve as a useful reference for public health investigators and officials.

Analysis of the genetic distribution among members of Clostridium botulinum group I using a novel multilocus sequence typing (MLST) assay

Clostridium botulinum is the etiological agent of botulism. Due to food-borne poisoning and the potential use of the extremely toxic botulinum neurotoxin (BoNT) from C. botulinum in bioterror or biocrime related actions, reliable high resolution typing methods for discriminating C. botulinum strains are needed. Partial sequencing of the adk, atpH, gyrB, proC, rpoD and spo0A genes from 51 various C. botulinum/sporogenes isolates was performed, resulting in 37 different sequence types (STs). Analysis of the sequence data revealed a genetic distribution in five larger clusters with a loose correlation to the BoNT serotypes. The developed MLST assay had a slightly lower resolution ability when compared to the MLVA (multilocus variable number of tandem repeat analysis), but the two methods resulted in similar subclusters of the strains possessing the BoNT serotypes A, B and F. The current work presents the development of a novel MLST assay useful for genotyping C. botulinum related to basic phylogenetic research and trace-back analysis in microbial forensic studies.

Enterotoxin gene profiles ofStaphylococcus aureusisolated from milk and dairy products in Italy

Staphylococcal foodborne intoxication, occurring after consumption of staphylococcal enterotoxins (SEs) in food, is considered one of the most common forms of bacterial foodborne outbreaks worldwide. Milk and dairy products account for 5% of all the incriminated foods in staphylococcal outbreaks, referring to Europe. The distribution of genes encoding for enterotoxins in Staphylococcus aureus strains is highly variable, with some carried on stable regions of the chromosome and others carried on mobile genetic elements. The aim of this study was to analyse the distribution of genes encoding for SEs in Staph. aureus strains isolated from milk and dairy products. In the period from January 2010 to June 2011, a total of 1245 dairy samples (848 of raw milk and 397 of dairy products) were collected and analysed for detection of genes encoding for 11 SEs and SEls (SEA, SEB, SEC, SED, SEE, SEG, SEH, SEI, SER SElJ and SElP) according to the procedures of the Italian National Reference Laboratory for coagulase-positive Staphylococci including Staph. aureus. Staphylococcus aureus strains were isolated in 481 (39%) samples. Of the 481 isolates of Staph. aureus tested, 255 (53%) were positive for one or more SE genes, and thirty-five different enterotoxin gene profiles were distinguished among the isolates. ser gene, found in 134 (28%) of the isolates, was the most frequent, followed by sed (25%) and selj genes (25%). The identification of new SEs increased the isolation frequency of enterotoxigenic staphylococci, thus suggesting that the pathogenic potential of Staph. aureus may be of greater importance than previously thought. Further studies are needed to quantify the expression of these new enterotoxins, and to assess their contribution to foodborne disease burden. The analyses targeted 11 staphylococcal enterotoxins genes and 35 different enterotoxin gene profiles were distinguished among the isolates. A total of 255 Staph. aureus isolates were positive for one or more SE genes while ser gene was the most prevalent. In 93% of the isolates bearing genes located on the enterotoxin gene cluster (n = 89), both seg and sei genes were present.

The occurrence of N-nitrosamines, residual nitrite and biogenic amines in commercial dry fermented sausages and evaluation of their occasional relation

Regarding food borne intoxications, the accumulation of biogenic amines must be avoided in all kinds of food products. Moreover, biogenic amines can function as precursors for the formation of carcinogenic N-nitrosamines when nitrite is present. To estimate the food safety of the dry fermented sausages available on the Belgian market, a screening of the residual sodium nitrite and nitrate contents, biogenic amines and volatile N-nitrosamine concentrations was performed on 101 samples. The median concentrations of residual NaNO2 and NaNO3 were each individually lower than 20mg/kg. In general, the biogenic amine accumulation remained low at the end of shelf life. Only in one product the amounts of cadaverine and putrescine reached intoxicating levels. Concerning the occurrence of N-nitrosamines, only N-nitrosopiperidine and N-nitrosomorpholine were detected in a high number of samples (resp. 22% and 28%). No correlation between the presence of N-nitrosamines and the biogenic amines content was observed. Although the N-nitrosamines could not been linked to specific product categories, the occurrence of N-nitrosopiperidine could probably be attributed to the use of pepper.

Assessment of bacterial load in broiler chicken meat from the retail meat shops in Chitwan, Nepal

INTRODUCTION: Keeping quality of meat and meat related food hazard relates to microbes present in the meat during processing or storage. The poultry slaughtered and dressed under Chitwan conditions carrying high initial contamination would be present in meat as inherent contamination in the finished products. MATERIALS AND METHODS: This cross-sectional study included 26 fresh broiler meat samples from registered retail shops. The samples were subjected to bacteriological analysis such as total viable count (TVC), total enterobacteriaceae count (TEC), total coliform count (TCC) and total staphylococcal count (TSC). Also, the samples were analyzed for the detection of Salmonella spp. and identified by different biochemical tests. RESULTS: The mean counts in log10±SE colony forming units per gram (cfu/g) for Bharatpur, Ratnanagar and Institute of Agriculture and Animal Science (IAAS) vicinity were obtained as 11.1±0.3, 11.5±0.3 and 12.2±0.5 TVC; 8.5±0.2, 9.2±0.3 and 10.2±0.4 TEC; 6.5±0.3, 7.6±0.3 and 8.4±0.5 TCC; 6.5±0.2, 6.8±0.3 and 7.7±0.4 TSC respectively. No samples were found to be within the permissible limits given by different agencies. Prevalence of Salmonella spp. in retail broiler meat in Chitwan was found 46.2%. CONCLUSION: The retail broiler meat samples from the locations contain high count of bacteria suggesting deplorable state of hygienic and sanitary practices. The presence of Salmonella and Staphyloccus aureus organisms over the permissible limits are of special concern because these account for potential food borne intoxication. So, the need for microbial assessment of fresh meats can be emphasized. DOI: http://dx.doi.org/10.3126/ijim.v2i3.8671 Int J Infect Microbiol 2013;2(3):99-104

Evaluation of Non-bacterial factors contributing to histamine accumulation in fish fillets

Histamine is one cause of scombroid foodborne poisoning. The bacterial decarboxylation of amino acids leads to the formation of biogenic amines such as histamine. This study examined histamine accumulation in tuna and yellowtail fillets that had been sterilized by gamma irradiation to confirm whether factors other than bacterial activity are able to induce histamine accumulation. Fish fillets were sterilized by gamma irradiation at 35 kGy and stored for 7 days at 5, 15, or 25 °C, and the resulting histamine concentrations were measured. The histamine concentrations in all tested samples of tuna and yellowtail were below the detection limit of the assay used (<10 mg/kg). In contrast, the tuna and yellowtail meats inoculated with Morganella morganii, a known histamine-producing bacterium, showed significant histamine accumulation at 15 and 25 °C. These results indicated that non-bacterial factors do not promote histamine accumulation. Therefore, the proper control of histamine-producing bacteria is both necessary and sufficient to prevent histamine accumulation.

Determination and Frying Loss of Histamine in Striped Marlin Fillets Implicated in a Foodborne Poisoning

An incident of foodborne poisoning causing illness in 67 victims due to ingestion of fried fish fillets occurred in June 2011, in southern Taiwan. Of the five suspected fish fillets, one fried sample contained 62.0 mg/100 g and one raw sample contained 89.6 mg/100 g histamine, levels which are greater than the potential hazard action level (50 mg/100 g) in most illness cases. Given the allergy-like symptoms of the victims and the high histamine content in the suspected fish samples, this foodborne poisoning was strongly suspected to be caused by histamine intoxication. Five histamine-producing bacterial strains capable of producing 59 to 562 ppm of histamine in Trypticase soy broth supplemented with 1.0% L-histidine were identified as Enterobacter aerogenes (two strains), Raoultella ornithinolytica (two strains), and Morganella morganii (one strain). The degradation loss of histamine in suspected raw fillets was 28% after they were fried at 170°C for 5 min.