PMID:22429258

Citation	Tabanelli, G, Torriani, S, Rossi, F, Rizzotti, L and Gardini, F (2012) Effect of chemico-physical parameters on the histidine decarboxylase (HdcA) enzymatic activity in Streptococcus thermophilus PRI60. J. Food Sci. 77:M231-7
Abstract	In this study the activity of the histidine decarboxylase (HdcA) of Streptococcus thermophilus PRI60 was determined during growth and in crude enzyme preparations to evaluate its hazardousness in dairy products. The effect of different pH values, lactose availability, NaCl concentration, and growth temperature on histamine production was evaluated in M17 medium during 168 h incubation. In each case, the production of histamine increased concomitantly with the cell number with a relatively small further rise during the stationary phase. In all cultures the maximum histamine levels were reached at the end of active growth. Histamine was detectable (10 to 55 mg/L) even when growth was strongly inhibited. The HdcA enzyme in crude cell-free extracts was mostly active at acidic pH values common in dairy products. NaCl concentrations lower than 5% did not affect its activity. The enzyme was quite resistant to heat treatments resembling low pasteurization, but was inactivated at 75 °C for 2 min. Given the features of the enzyme studied, efforts must be dedicated to a thorough risk analysis and development of strategies to contrast the presence of histaminogenic S. thermophilus strains in products from raw or mildly heat-treated milk. PRACTICAL APPLICATION: During its growth Streptococcus thermophilus can produce histamine over a wide range of conditions encountered in cheesemaking and cheese ripening. The histidine-decarboxylase is even more active in cell-free extract and histamine can be accumulated independently of cell viability.
Links	PubMed Online version:10.1111/j.1750-3841.2012.02628.x
Keywords	Bacterial Proteins/chemistry; Bacterial Proteins/metabolism; Colony Count, Microbial; Dairy Products/adverse effects; Dairy Products/analysis; Dairy Products/microbiology; Enzyme Stability; Food Contamination/prevention & control; Histamine/adverse effects; Histamine/metabolism; Histidine Decarboxylase/chemistry; Histidine Decarboxylase/metabolism; Hydrogen-Ion Concentration; Kinetics; Lactose/metabolism; Microbial Viability; Osmolar Concentration; Pasteurization; Physicochemical Phenomena; Sodium Chloride/metabolism; Streptococcus thermophilus/enzymology; Streptococcus thermophilus/growth & development; Streptococcus thermophilus/metabolism; Temperature
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
STRTR:E7AXS8		GO:0004398: histidine decarboxylase activity	ECO:0000270:		F		Figure 2A shows that at the pH values 7.0, 6.2, and 5.5 the OD600 rapidly increased between 8 and 24 h of incubation reaching at 48 h the maximum values, corresponding to cell concentrations between 9.2 and 8.8 log CFU/mL. Also, in Figure in 3A, histamine rapidly accumulated at pH 7.0, 6.2, and 5.5 and a maximum concentration of about 350 mg/L was reached after 24 h. In both cases the production of histamine increased concomitantly with the cell number with a relatively small further rise during the stationary phase. In all cultures the maximum histamine levels were reached at the end of active growth. Histamine was detectable (10 to 55 mg/L) even when growth was strongly inhibited.The HdcA decarboxylase of this strain is very active since the exponential phase under different conditions characterizing the 1st step of the cheesemaking process. In addition, the enzyme is even more active outside the cells and its action is not significantly limited by the conditions found during the cheese ripening process. In this framework, the death and lysis of the starter cultures can be a factor which strengthens the risk of histamine accumulation during cheese ripening when temperature, pH, and NaCl concentration allow an intense activity of this HdcA enzyme.	complete CACAO 4004

References

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