Cronobacter MLST Primers and Protocols

Genes

The Cronobacter spp. MLST scheme uses fragments of the following seven house-keeping genes:

• ATP synthase beta chain (atpD)
• Elongation factor G (fusA)
• Glutaminyl-tRNA synthetase (glnS)
• Glutamate synthase large subunit (gltB)
• DNA gyrase subunit B (gyrB)
• Translation initiation factor IF-2 (infB)
• Phosphoenolpyruvate synthase (pps)

PCR amplification

Reaction conditions for all the primers were as follows: initial denaturation at 96°C for 1 min; 30 cycles of denaturation at 96°C for 1 min, primer annealing at 58°C for 1 min, extension at 72°C for 2 min; followed by a final extension step of 72°C for 5 min. Each 50 µl amplification reaction mixture comprised: 10 µl Q solution (Qiagen), 4.0 µl chromosomal DNA (5-20 ng/µl), 2.0 µl forward primer (10 pmol/µl), 2.0 µl reverse primer (10 pmol/µl), 5.0 µl 10x PCR buffer (Qiagen, contains 15 mM MgCl2), 1.0 µl dNTP solution (Qiagen, 10 mM each dNTP), 0.25 µl Taq polymerase (Qiagen, 5 Units/µl) and 25.75 µl PCR-grade water. All Qiagen solutions from PCR CORE Kit (Cat No. 201225).

The amplification product was then purified using MinElute UF plates (Qiagen) following the manufacturers protocol before being used in a sequencing reaction. Sequencing was carried out on each DNA strand with BigDye Terminator Ready Reaction Mix v3.1 (PE Biosystems, Foster City, US) under standard sequencing conditions according to the manufacturer's protocol. Unincorporated dye terminators were removed by precipitation with 95% alcohol. The reaction products were separated and detected on an ABI PRISM genetic analyser 3100 (PE Biosystems) using a standard sequencing module with a Performance Optimised Polymer and 5 cm array.

The primers used in MLST analysis of Cronobacter spp. are listed below.

Sequencing