Mining for sensitive and reliable species-specific primers for PCR for detection of Cronobacter sakazakii by a bioinformatics approach

Although several studies have reported PCR assays for distinguishing Cronobacter sakazakii from other species in the genus, reports regarding assay sensitivity and specificity, as well as applications for food testing, are lacking. Hence, the objective of this study was to develop a sensitive and reliable PCR-based method for detection of C. sakazakii by screening for specific target genes. The genome sequence of C. sakazakii in the Gen Bank database was compared with that of other organisms using BLAST. Thirty-eight DNA fragments unique to C. sakazakii were identified, and primers targeting these sequences were designed. Finally, 3 primer sets (CS14, CS21, and CS38) were found to be specific for C. sakazakii by PCR verification. The detection limit of PCR assays using the 3 pairs of primers was 1.35 pg/mu L, 135 fg/mu L, and 135 fg/mu L, respectively, for genomic DNA, and 5.5 x 10(5), 5.5 x 10(3), 5.5 x 10(3) cfu/ mL, respectively, using pure cultures of the bacteria, compared with 13.5 pg/mu L and 5.5 x 10(5) cfu/mL for primer set SpeCronsaka, which has been previously described. Cronobacter sakazakii were detected in artificially contaminated powdered infant formula (PIF) by PCR using primer sets CS21 and CS38 after 8 h of enrichment. The detection limit was 5.5 x 10(-1) cfu/10 g of PIF. Thus, the PCR assay can be used for rapid and sensitive detection of C. sakazakii in PIF.