# 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. Commonly for the isolation and detection of microorganisms, such as enterobacteria in various samples, when the culture is viable, phenotypic identification is used, which includes the visible characteristics of bacteria, such as morphology, serological, biochemical, and metabolic properties using various simple, enriched media that are differential and/or selective [69]. For the isolation and growth of _Citrobacter_ sp., different culture media can be used through culture, such as Luria-Bertani (LB) agar, tryptic soy agar (TSA), blood agar (BA), MacConkey agar, cystine-lactose-electrolyte-deficient (CLED) agar, Salmonella-Shigella (SS) agar, xylose lysine deoxycholate (XLD) agar, Eosin Methylene Blue (EMB) agar, and Violet Red Bile Glucose agar (VRBG), among others [21, 38, 40, 41, 47, 50]. The identification or confirmation of other enterobacteria, even at the species level, can be achieved by analysis of enzymatic activities, metabolic capacity, antigenic determinants, or susceptibility to bactericidal agents [21, 35, 37, 40, 41, 47, 70]. Within the biochemical identification tests, all the species were identified as _Citrobacter_ ferment glucose with the production of gas (Table 2). The susceptibility pattern of the isolates helps to identify _C. Roseri_, which has a susceptibility pattern to antibiotics such as _Klebsiella_ (resistant to ampicillin and ticacillin) and is sensitive to ciprofloxacin, carbapenemers, third-generation cephalosporions, piperacillin-tazobactam, aminoglycosoides, and trimethoprim sulfamethoxazole [37]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Test**} & _Citrobacter_ & _Escherichia_ & _Salmonella_ & _Edwardsiella_ & _Klebsiella_ & **spp.** & _Serratia_ sp.** \\  & **spp.** & **spp.** & **spp.** & **spp.** & & \\ \hline Mobility & \(+\) & \(+\) & \(+\) & \(+\) & \(-\) & \(+\) \\ \hline Gram stain & \(-\) & \(-\) & \(-\) & \(-\) & \(-\) & \(-\) \\ \hline Urease & \(-\) & \(-\) & \(-\) & \(-\) & \(+\) & \(-\) \\ \hline \(\beta\)-galactosidase & \(+\) & \(+\) & \(-\) & \(-\) & \(+\) & \(+\) \\ \hline Citrate & \(+\) & \(-\) & \(+\) & \(-\) & \(+\) & \(+\) \\ \hline Methyl red & \(+\) & \(+\) & \(+\) & \(+\) & \(-\) & \(-/+\) \\ \hline Voges– & \(-\) & \(-\) & \(-\) & \(-\) & \(-\) & \(+\) \\ Proskauer & \(-\) & \(+\) & \(-\) & \(+\) & \(-\) & \(-\) \\ \hline Indole & \(-\) & \(-\) & \(-\) & \(-\) & \(-\) & \(-\) \\ \hline Alanine & \(-\) & \(-\) & \(-\) & \(-\) & \(-\) & \(-\) \\ deaminase & & \(+\) & \(+\) & \(+\) & \(+\) & \(+\) \\ \hline Gas from glucose & \(+\) & \(-/+\) & \(-/+\) & \(+/-\) & \(-\) & \(-\) \\ \hline Ornithine & \(-/+\)a & \(+/-\) & \(+\) & \(+\) & \(-\) & \(+\) \\ \hline \hline \end{tabular} +: positive reaction; \(-:\) negative reaction. \(+/-:\) 50 to 90% of the strains are positive; \(-/+:\) 50 to 90% of the strains are negative; \(-/+:\) 50 to 90% of the strains are negative for _C. freundili_.  
\end{table} 
Table 2: Identification tests or biochemical confirmation of the genus _Citrobacter_ spp. of other enterobacteria [21, 41, 71, 72]. Bacteria belonging to the genus _Citrobacter_ spp. are closely related to _Salmonella_. Therefore, some similarities in cell surface antigens and biochemical properties may occur between them [73]. Species such as _Citrobacter freundii_, in its isolation and identification, can result in the false identification of these bacteria, such as _Salmonella_ sp. or _Proteus_ sp., so it can lead to more tests (Table 3) and require more time to obtain the most detailed results with the increase in the cost of analysis [41].