Introduction
Method
The method described here contains both a real-time PCR method for rapid screening and a cultural method for the detection/isolation of Cronobacter spp. (3). Chromogenic agars are used to isolate the culture for confirmation. A pre-enrichment step is used to grow the bacteria to an amount (≥ 103 CFU/ mL) detectable by PCR and chromogenic agars. The cultural portion of this method is a complete detection/isolation method, so it can be used as a stand alone method if PCR technology is unavailable. The PCR portion of the method is a screening method, whose positive results should always be confirmed with the cultural method. The PCR method may be used to confirm pure cultures as Cronobacter spp. This method was validated in pre-collaborative and collaborative studies (1,2).
The inclusivity of this method was determined by analyzing 51 different Cronobacter strains representing the six Cronobacter species that were isolated from foods, clinical samples, environmental surfaces, and nationally/internationally recognized culture depositories. The origin and source of each strain are listed in the Inclusivity Table (A). Each strain was enriched in brain heart infusion (BHI) broth and diluted in buffered peptone water (BPW) to approximately 10 times the limit of detection. The diluted cultures were then tested according to this method.
The exclusivity of this method was determined by testing 42 non-Cronobacter strains. The source and origin of each strain are listed in the Exclusivity Table (B). Each strain was enriched in BHI broth. These incubated cultures were tested according to this method.