# A Review on Food Safety: The Case of _Citrobacter_ sp., Fish and Fish Products
## 5 Isolation and Detection of Enterobacteria in Food Case: _Citrobacter_ sp.
However, it has been shown that histamine can accumulate in fish and reach toxic levels even at temperatures as low as 5 \({}^{\circ}\)C. At these temperatures, and after exposure to brief periods of storage at high temperatures ranging from 15 to 20 \({}^{\circ}\)C, they form large amounts of histamine even though bacterial growth ceases; this is because the decarboxylase enzyme synthesized during the brief periods of permanence of the fish at high temperatures is enough for subsequent prolonged production of histamine [96]. The toxicity of biogenic amines is related to factors associated with consumers, including the foods consumed, individual susceptibility, health status, drug use, etc., which makes it difficult to indicate the levels of toxicity in food [54]. Sanitary regulations established around the world have been developed to guarantee the safety of fishing products by controlling and reducing various contaminating hazards, such as histamine. Therefore, in terms of food safety regulation, the European Union presents Regulation (EC) 852/2004 on the hygiene of food products that establishes the hygiene conditions and practices applied to all stages of production, transformation, distribution, and exports of food. Regulation (EC) 853/2004 establishes specific hygiene standards for food of animal origin, including the application of procedures based on the principles of hazard analysis and critical control points, as well as conservation requirements for products of fishing, considering the use of temperatures between 0 and 4 \({}^{\circ}\)C. The council directive 91/493/EEC and regulation (EC) 2073/2005 that establish the sampling and analysis of products indicate that when nine samples are taken from a lot of fish for histamine analysis, the average value should not be greater than 100 ppm in fish, scombrids, and cupleids families, marketed during their useful life [54; 66; 68]. The Food and Drug Administration (FDA) has established regulatory limits considering that fish with histamine ratios of \(\geq\)50 ppm are in a state of decomposition, and fish containing histamine at \(\geq\)500 ppm are a danger to humans and public health [54; 68]. The Indian Food Safety and Standards Authority has proposed the maximum acceptable limit for histamine as 100 mg/kg [62]. Meanwhile, the sanitary regulations for processed, fresh, refrigerated, and frozen fish products in Latin American countries, such as Mexico, include official Mexican standard NOM-242-SSA1-2009, which establishes a maximum limit of 100 mg/kg of histamine in fish of the _Clupeidae_, _Scombridae_, _Scombridae_, _Scombridae_, and _Coryphaentidae_ families. On the other hand, regarding the contamination of fishery products by _Citrobacter_ sp., several countries around the world, including Mexico, do not have sanitary regulations or specific limits for the presence of this microorganism associated with gastrointestinal diseases caused by food consumption and part of the histamine-generating microbiota in post-harvest fish. However, being part of the enterobacteria family, it has been pointed out that fecal coliforms, _E. coli_, and enteric pathogens such as _Salmonella_ spp. are considered some of the microbiological indicators to determine contamination and health risk in various fresh, refrigerated, and frozen products intended for commercialization and human consumption [79; 97; 98; 99]. This may have its advantages in terms of investment in time to obtain results, equipment, and materials for use in a microbiological analysis, in addition to the fact that analysis of these indicators can be associated with a greater risk of disease due to the consumption of these products contaminated with their respective causal agents. On the other hand, disadvantages may be that analysis of indicators such as coliforms involves the detection and generalized proportion of a diverse group of microorganisms in which _Citrobacter_ may or may not be present in samples.