Growth of Salmonella enterica in model mixed cultures during a two-step enrichment.
Growth of Salmonella enterica was studied in model mixed cultures with Citrobacter freundii or Escherichia coli in buffered peptone water (BPW) and in Rappaport-Vassiliadis medium with soya (RVS) with modified concentrations of MgCl2 and malachite green, and at modified incubation temperatures. Selected S. enterica strains were inoculated in BPW (10(0) cfu/ml) together with selected strains of Citrobacter freundii (up to 10(8) cfu/ml) or selected strains of Escherichia coli (up to 10(8) cfu/ml), incubated overnight and then subcultured (1: 100) in RVS variants. Growth of individual bacterial species was followed by the quantitative real-time polymerase chain reaction (PCR). Optimal culture conditions during the second selective step were: MgCl2.6 H2O concentration of 29 g/l, malachite green concentration of 36 mg/1l, and the incubation temperature of 41.5 degrees C. Citr. freundii was found to be a potent competitor and E. coli was a weaker competitor. At optimal culture conditions, competition was reduced and the density of S. enterica cultures reached the level of 10(4) cfu/ml after not later than 2 h of selective enrichment. The results obtained provide a basis for the development of a short two-step enrichment to be used in rapid real-time PCR-based methods for the detection of S. enterica in food and other matrices.
Krascsenicsová
Klára
K
Department of Microbiology and Molecular Biology, Food Research Institute, Bratislava, Slovakia.
Kaclíková
Eva
E
Kuchta
Tomás
T
D001431:Bacteriological Techniques; D002954:Citrobacter / Q000254:growth & development*; D015169:Colony Count, Microbial; D003470:Culture Media; D004269:DNA, Bacterial / Q000032:analysis; D017753:Ecosystem; D004926:Escherichia coli / Q000254:growth & development*; D005506:Food Contamination / Q000032:analysis; D015636:Magnesium Chloride / Q000378:metabolism; D008954:Models, Biological; D016133:Polymerase Chain Reaction; D012394:Rosaniline Dyes / Q000378:metabolism; D019779:Salmonella enterica / Q000235:genetics / Q000254:growth & development* / Q000302:isolation & purification; D030262:Soybean Proteins / Q000378:metabolism
D003470:Culture Media; D004269:DNA, Bacterial; D012394:Rosaniline Dyes; D030262:Soybean Proteins; D015636:Magnesium Chloride; C005095:malachite green