DEVELOPMENT OF A DETECTION SYSTEM FOR HISTIDINE DECARBOXYLATING LACTIC-ACID BACTERIA BASED ON DNA PROBES, PCR AND ACTIVITY TEST

On the basis of the comparison of the nucleotide sequences of the hist idine decarboxylase genes (hdcA) of Lactobacillus 30A and Clostridium perfringens and the amino acid sequences of these histidine decarboxyl ases and those of Lactobacillus buchneri and Micrococcus, oligonucleot ides unique to the hdcA genes were synthesized and used in PCR. All hi stidine-decarboxylating lactic acid bacteria gave a signal with primer set JV16HC/JV17HC in PCR. In addition to this primer set, CL1/CL2 and CL1/JV17HC were also useful for the detection of histamine-forming Le uconostoc aenos strains in PCR. The 150 base pair amplification produc t of the decarboxylating Leuc. aenos strain generated with primer set CL1/CL2 was sequenced. Alignment studies showed a high degree of relat edness among the hdcA gene products of Gram-positive bacteria. The amp lification products of the hdcA genes from Lact. buchneri and Leuc. ae nos were used to serve as a DNA probe in hybridization studies. All hi stidine-decarboxylating lactic acid bacteria gave a hybridization sign al with the DNA probes. In hybridization only one false-positive signa l with a Lactobacillus lindneri strain was observed, which was anticip ated to contain a truncated hdcA gene. In addition to these DNA probe tests, a simple and reliable activity test is presented, which can be used during starter selection to test strains for histidine decarboxyl ase activity.