Abstract
A qualitative microplate screening method, using both low nitrogen (LND) and low glucose (LGD) decarboxylase broths, was used to evaluate the biogenic amine (BA) forming capacity of bacteria present in two types of Spanish ripened cheeses, some of them treated by high hydrostatic pressure. BA formation in decarboxylase broths was later confirmed by High Performance Liquid Chromatography (HPLC). An optimal cut off between 10–25 mg/L with a sensitivity of 84% and a specificity of 92% was obtained when detecting putrescine (PU), tyramine (TY) and cadaverine (CA) formation capability, although these broths showed less capacity detecting histamine forming bacteria. TY forming bacteria were the most frequent among the isolated BA forming strains showing a strong production capability (exceeding 100 mg/L), followed by CA and PU formers. Lactococcus, Lactobacillus, Enterococcus and Leuconostoc groups were found as the main TY producers, and some strains were also able to produce diamines at a level above 100 mg/L, and probably ruled the BA formation during ripening. Enterobacteriaceae and Staphylococcus spp., as well as some Bacillus spp. were also identified among the BA forming bacteria isolated.
Highlights
Tyrosine decarboxylase test showed an area under the Receiver Operating Characteristic (ROC) curve (AUC) around 0.98, with an optimal cut-off value at 25 mg/L and 20 mg/L of TY on Low Nitrogen Decarboxylase Broth (LND) and Low Glucose Decarboxylase Broth (LGD) broths, respectively
The microplate screening method allows for a rapid preliminary selection of strains with low decarboxylase activity, with a detection limit estimated around 50 mg/L
The data indicates that, in general, the specific amino acid decarboxylase assay with LND and LGD broths have satisfactory diagnostic parameters to discriminate bacterial isolates with ornithine, lysine and tyrosine decarboxylases
Summary
Amino acid decarboxylase activity has been described for several groups of microorganisms, such as Enterobacteriaceae, Pseudomonas spp, Enteroccoccus, Microccoccus and Lactic Acid Bacteria (LAB) These BA-producing organisms may be part of the microbiota of the raw materials or may be introduced by contamination during or after processing of foodstuffs [4,7,8,9,10,11,12,13,14]. Sumner et al [19] isolated a strain of Lactobacillus buchneri (strain St2A) from a Swiss cheese involved in an outbreak of HI poisoning occurred in the USA in 1980 that was able to form high amounts of HI This LAB, later classified al L. parabuchneri, is able to grow and produce histamine at refrigeration temperatures [20]. Enterobacteriaceae, Staphylococcus spp. or Bacillus spp. have been related to the accumulation of diamines in foods, including cheese, and TY and/or HI [8,17,21,22]
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