Improvement of Enterobacteriaceae enrichment broth by supplementation with sodium citrate for detection of Cronobacter sakazakii using real-time PCR

Abstract

Enterobacteriaceae enrichment (EE) broth, a selective enrichment medium for Cronobacter sakazakii detection, has been shown to contain polymerase chain reaction (PCR) inhibitors. Therefore, a modified enrichment broth was developed, wherein possible PCR inhibitors, brilliant green and bile salts, were substituted with sodium citrate. Investigations were conducted to determine whether realtime PCR detection of C. sakazakii in powdered infant formula and dried vegetables with this modified medium improved compared with conventional culture methods. The detection rate of the modified EE broth was significantly higher (p<0.05) than that of the conventional EE broth for both types of food. For dried pumpkin samples, real-time PCR after culturing in modified EE broth yielded significantly higher detection rates and selectivity than those achieved using conventional culture in Druggan-Forsythe-Iversen agar. These results show that real-time PCR after enrichment in the modified EE broth may be an effective screening method for detection of C. sakazakii.