The growth profile, thermotolerance and biofilm formation of Enterobacter sakazakii grown in infant formula milk

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Abstract
Aims: To study the growth, thermotolerance and biofilm formation of the emergent pathogen Enterobacter sakazakii in infant formula milk (IFM). Methods and Results: The temperature range, death kinetics and biofilm formation of E. sakazakii were determined using impedance microbiology and conventional methods. In IFM the organism grew as low as 6°C and optimally at 37–43°C. In faecal coliform tests, 23% of strains (n = 70) produced gas from lauryl sulphate broth (LSB) at 44°C after 48 h incubation. Three strains failed to grow in LSB at any of the temperatures. The D-value of cells suspended in IFM was determined between 54 and 62°C. The resultant z-value was 5·7°C. The organism was able to adhere and grow on latex, polycarbonate, silicon and to a lesser extent stainless steel. Conclusions: Enterobacter sakazakii was able to grow at refrigeration temperatures and on infant-feeding equipment. The thermotolerance of the organism was similar to other Enterobacteriaceae and should be killed during standard pasteurization treatment. Significance and Impact of the Study: Enterobacter sakazakii has been associated with infant meningitis through consumption of contaminated IFM. Enterobacter sakazakii is able to grow in IFM during storage at refrigeration temperatures and attach to infant-feeding equipment, which may become reservoirs of infection.