Abstract
Cronobacter species are opportunistic foodborne pathogens involved in neonatal infections from powdered infant formula (PIF). In this study, a novel saltatory rolling circle amplification (SRCA) method has been developed for detecting Cronobacter spp. in PIF. 16 of Cronobacter spp. strains and 32 of non-Cronobacter strains were examined by using the DNA-directed RNA polymerase subunit beta (rpoB) gene. All Cronobacter strains were identified in pure cultures, whereas no SRCA products were found in non-Cronobacter strains. The detection limits were 3.4 × 102 CFU/mL through observing the white precipitate by naked eye, while 3.4 × 101 CFU/mL by fluorescence visualization. After enrichment, the detection limits of SRCA method in PIF were 8.7 × 100 CFU/g and 8.7 × 10−1 CFU/g by visualization with white precipitate and fluorescence, respectively. Compared with the conventional PCR method, the SRCA has at least 100-fold higher sensitivity and 100-fold lower detection limit. In addition, 85 of PIF samples were investigated for the Cronobacter contamination, and the results were 100% sensitivity, 97.62% specificity and 97.65% accuracy compared with the ISO method. Therefore, the results show that SRCA is a sensitive and visual detection method for the detection of Cronobacter spp. in PIF with great potential.
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