For the selective pre-enrichment medium for Cronobacter sakazakii
LAURYL SULPHATE TRYPTOSE BROTH, MODOFIED (as per ISO) is used for the selective enrichment of Enterobacter sakazakii. E. sakazakii is currently considered an emerging pathogen responsible for unweaned babies, risking severe meningitis and necrotic enterocolitis that can be the cause of a mortality rate between 40 and 80%. Lauryl Sulphate Tryptose Broth, Modified promotes a rich growth and copious gas production from small inocula of coliform organisms. Aerobic sporing bacteria are completely inhibited. Plant and Animal tissue enzymatic digest provides the nitrogen, carbon compounds, vitamins and amino acids. Lactose is the fermentable sugar. Sodium chloride maintains the osmotic balance of the medium. Dipotassium phosphate and Mono potassium phosphate controls the pH during fermentation of Lactose. The ISO normative 22964 recommends this medium as a selective enrichment with the addition of Vancomycin and incubation at 44ºC. All the tubes must be subcultured in the chromogenic agar for the isolation of Enterobacter sakazakii. Lactose-positive bacteria metabolize lactose with gas formation is indicated by using inverted Durham tubes. Incubate at the wished temperature for 24 ± 2 hours. In case of gas formation the Durham tubes rise or/and show bubbles. Turbidity of the medium accompanied by formation of gas within 48 hours is a positive presumptive test for the presence of Enterobacter sakazakii and/or other coliform organisms. Incubate at 44 ± 0.5ºC and observe for 24 ± 2 hours.