RAPID ENUMERATION OF ENTEROBACTER SAKAZAKII IN RECONSTITUTED MILK FORMULA BY FLUOROGENIC MOST‐PROBABLE‐NUMBER ASSAY USING 96‐WELL MICROTITER PLATE

Abstract

ABSTRACT A new method was developed to rapidly monitor the Enterobacter sakazakii viable counts in reconstituted infant milk formula. Ninety six–well microtiter plates were used to perform a miniaturized 10‐tube most‐probable‐number (MPN) enumeration protocol for E. sakazakii. This procedure is based on fluorogenic detection as a result of the growth and α‐glucosidase production from E. sakazakii in broth containing 4‐methylumbelliferyl‐α‐D‐glucoside (OK medium). The correlation between E. sakazakii counts by conventional plating and microtiter MPN methods was highly agreeable in 0.2% peptone water (R2 = 0.94) and reconstituted infant milk formula (R2 = 0.91). From these results, the new rapid method can quickly monitor E. sakazakii counts in infant milk formula with a high correlation with the conventional plating method. The results indicate that the microtiter MPN method required much shorter incubation times (<10 h) than the conventional plating method (<24 h) and provided a more economical way to monitor E. sakazakii, using selective and differential medium in end point determinations.