# A Review on Food Safety: The Case of _Citrobacter_ sp., Fish and Fish Products
## 4 _Citrobacter_ sp.
### Citrobacter, Histamine, and Food Diseases by Fish Consumption
On the other hand, histamine is a thermostable derivative of the decarboxylation of free histidine in fish muscle and derived products through the activity of microbial enzymes (histidine-decarboxylase), whose activity can be affected by factors such as temperature, pH, concentration of histidine, oxygen tension, and the presence of vitamins and coenzymes, and the most determining factors are temperature and pH (Figure 2) [53; 60]. The fish and fish products associated with high proportions of histidine in muscle and susceptible to decarboxylase activity are especially those of the Scombridae family, such as tuna (_Thununus thynunus thynunus_), mahi-mahi (_Coryphaena hippurus_), oily fish (_Pomatomus saltatrix_), sardines (_Sardine pilchardus_), mackerel (_Somber scombrus_), amberjack (_Seriola zonata_), and abalone (_Haliotiis_ spp.) [26; 53; 60; 32], as well as other species, such as dorado (_Coryphaena_ spp. ), anchoveta (_Engraulis_ spp. ), smooth (_Mugil curema_), and snook (_Centroomus undecimals_) [23; 59]. This amine is considered a health risk in the processing of fish for human or animal consumption. Once histamine is generated in fish, the potential to generate poisoning is high because it is thermostable, meaning it is not destroyed by any thermal process, whether it is cooking or sterilization, as well as storage temperatures, such as refrigeration and freezing [26; 32; 67]. As such, its detection is necessary to comply with tolerance levels, sanitary control, and protection of public health [23; 59]. The presence of histamine in a food is an indicator of poor microbiological quality and hygienic management of fish [56], as well as an indicator of the low quality of the raw material of products preserved by heat treatment, and an indicator of quality in fishmeal, where the content of biogenic amines reflects the state of freshness of the raw material from which the product was obtained [55]. Poisoning from consumption of histamine-contaminated fish can occur within a few minutes to a few hours after ingestion, and the duration of symptoms varies from a few hours up to 24 h and, in some cases, the toxic effects persist for several days [26; 68]. The levels to produce intoxication effects are 50 mg of histamine/100 g of fish [65]. In most cases of poisoning illness, histamine levels in fish exceed 200 ppm, frequently reaching above 500 ppm [68]. The symptoms of poisoning can be nausea, dyspnea, diarrhea, pruritus, urtic, heart palpitations, hyper or hypotension, headache, respiratory distress, and in severe cases, bronchospasms [26; 65; 66; 32; 68]. In addition, the effect of histamine can be enhanced by the presence of other amines, such as tyramine, putrescine and cadaverine, in which the latter has no biological activity, but they inhibit enzymes such as diamine oxidase and histamine N-methyltransferase in histamine metabolism [55; 66; 32]. Given the benign development  
Figure 2: Histamine formation by decarboxylation of histidine [55]. and the tendency for spontaneous resolution, patients often do not require treatment for poisoning, but if required, this can be gradual as symptoms appear. Treatments include gastric lavage, administration of cathartics, bronchodilators, and antihistamines, either orally or intravenously [32, 65]. Patients being treated with isoniaizid or monoamine oxidase inhibitors are more vulnerable to histamine poisoning and have more severe and prolonged symptoms because these drugs inhibit histamine metabolism. On the other hand, patients undergoing treatment with antihistamines block the effect of histamine, and it can be said that they are protected in a certain way; however, it has been pointed out that the prophylactic use of antihistamines is not justified [65].