RESUMO
This study evaluated the influence of parameters relevant for cheese making on histamine formation by Streptococcus thermophilus. Strains possessing a histidine decarboxylase (hdcA) gene represented 6% of the dairy isolates screened. The most histaminogenic, S. thermophilus PRI60, exhibited in skim milk a high basal level of expression of hdcA, upregulation in the presence of free histidine and salt, and repression after thermization. HdcA activity persisted in cell extracts, indicating that histamine might accumulate after cell lysis in cheese.
Assuntos
Queijo/microbiologia , Doenças Transmitidas por Alimentos , Histamina/biossíntese , Histidina Descarboxilase/genética , Streptococcus thermophilus/metabolismo , Transcrição Gênica , Animais , Descarboxilação , Microbiologia de Alimentos , Histidina Descarboxilase/análise , Histidina Descarboxilase/metabolismo , Leite/microbiologia , Dados de Sequência Molecular , Reação em Cadeia da Polimerase , Análise de Sequência de DNA , Streptococcus thermophilus/citologia , Streptococcus thermophilus/genéticaRESUMO
In this study, a tyrosine decarboxylase gene (tdcA) was identified in 1 among 83 Streptococcus thermophilus strains tested. Its sequence, nearly identical to that of a tdcA of Lactobacillus curvatus, indicated a horizontal gene transfer event. Transcription in milk and the formation of critical levels of tyramine were observed in the presence of tyrosine.
Assuntos
Leite/química , Streptococcus thermophilus/enzimologia , Tiramina/biossíntese , Tirosina Descarboxilase/genética , Tirosina Descarboxilase/metabolismo , Animais , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Queijo/microbiologia , Indústria de Laticínios , Leite/metabolismo , Dados de Sequência Molecular , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Análise de Sequência de DNA , Streptococcus thermophilus/genética , Streptococcus thermophilus/metabolismoRESUMO
Tetracycline-resistant Streptococcus thermophilus isolates from soft cheeses harbored the genes tet(S), tet(M), and tet(L). Molecular analysis of these genes revealed their expression, localization on plasmids or Tn916-Tn1545 family transposons, and their similarity with published sequences. The study highlights the importance of an accurate safety assessment of using S. thermophilus as a starter culture.
Assuntos
Queijo/microbiologia , Genes Bacterianos , Streptococcus thermophilus/efeitos dos fármacos , Streptococcus thermophilus/genética , Resistência a Tetraciclina , Técnicas de Tipagem Bacteriana , Análise por Conglomerados , Impressões Digitais de DNA , Elementos de DNA Transponíveis , DNA Bacteriano/química , DNA Bacteriano/genética , Genótipo , Dados de Sequência Molecular , Filogenia , Plasmídeos , Técnica de Amplificação ao Acaso de DNA Polimórfico , Análise de Sequência de DNA , Homologia de Sequência , Streptococcus thermophilus/isolamento & purificaçãoRESUMO
In the present study, 20 enterococci belonging to the species Enterococcus faecalis (12 strains), Enterococcus faecium (4), Enterococcus durans (2), Enterococcus hirae (1) and Enterococcus mundtii (1) and originating from a total production chain of swine meat commodities were analysed to investigate the diversity of their tetracycline resistance gene tet(M). PCR-RFLP and sequence analysis showed that the tet(M) gene of most strains can be correlated with the Tn916 transposon. Conversely, tet(M) of six E. faecalis and the E. hirae strain, all isolated from pig faecal samples, may be associated with previously undescribed members of the Tn916-1545 transposon family. In vitro filter conjugation trials showed the ability of 50% of the enterococcal strains, including E. mundtii, to transfer the tet(M) gene (and the associated Tn916 and new transposons) to E. faecalis or Listeria innocua recipient strains. tet(M) gene transfer to L. innocua recipient was also directly observed in meat food products. Collectively, these sequence and conjugation data indicate that various transposons can be responsible of the spread of tetracycline resistance in enterococci and validate the opinion that Enterococcus species are important sources of antibiotic resistance genes for potentially pathogenic bacteria occurring in the food chain.
Assuntos
Proteínas de Bactérias/genética , Elementos de DNA Transponíveis , Enterococcus/efeitos dos fármacos , Enterococcus/genética , Transferência Genética Horizontal , Carne/microbiologia , Suínos/microbiologia , Resistência a Tetraciclina , Animais , Análise por Conglomerados , DNA Bacteriano/química , DNA Bacteriano/genética , Enterococcus/isolamento & purificação , Enterococcus faecalis/efeitos dos fármacos , Enterococcus faecalis/genética , Enterococcus faecalis/isolamento & purificação , Enterococcus faecium/efeitos dos fármacos , Enterococcus faecium/genética , Enterococcus faecium/isolamento & purificação , Fezes/microbiologia , Dados de Sequência Molecular , Filogenia , Análise de Sequência de DNA , Homologia de SequênciaRESUMO
Streptococcus thermophilus is a lactic acid bacteria (LAB) widely used in milk fermentation processes as a starter culture. In this work the genetic diversity of S. thermophilus isolates from different sources was analyzed using Amplified Fragment Length Polymorphism fingerprinting (AFLP). Since this is the first report that indicates the application of AFLP in order to study genotypic polymorphism in S. thermophilus species, an optimization of experimental conditions was carried out to decide the optimal AFLP analysis protocol. Furthermore the fingerprinting resolutions of AFLP and RAPD (Random Amplified Polymorphic DNA) were evaluated and compared. The overall data suggest that genotypic characterization performed by AFLP provide a better view of microbial diversity of S. thermophilus, indicating that RAPD is less discriminating than AFLP. The successful use of AFLP analysis in the characterization of S. thermophilus strains reported in this study suggests the potential uses for this technique to define the whole-genome diversity of each specific strain, as an alternative to the fingerprinting methods used till now.