Effectiveness of Disinfectants in Killing Enterobacter sakazakii in Suspension, Dried on the Surface of Stainless Steel, and in a Biofilm

Abstract

The effectiveness of 13 disinfectants used in hospitals, day-care centers, and food service kitchens in killing Enterobacter sakazakii in suspension, dried on the surface of stainless steel, and in biofilm was determined. E. sakazakii exhibited various levels of resistance to the disinfectants, depending on the composition of the disinfectants, amount and type of organic matrix surrounding cells, and exposure time. Populations of planktonic cells suspended in water (7.22 to 7.40 log CFU/ml) decreased to undetectable levels (<0.30 log CFU/ml) within 1 to 5 min upon treatment with disinfectants, while numbers of cells in reconstituted infant formula were reduced by only 0.02 to 3.69 log CFU/ml after the treatment for 10 min. The presence of infant formula also enhanced the resistance to the disinfectants of cells dried on the surface of stainless steel. The resistance of cells to disinfectants in 6-day-old and 12-day-old biofilms on the surface of stainless steel was not significantly different. The overall order of efficacy of disinfectants in killing E. sakazakii was planktonic cells > cells inoculated and dried on stainless steel > cells in biofilms on stainless steel. Findings show that disinfectants routinely used in hospital, day-care, and food service kitchen settings are ineffective in killing some cells of E. sakazakii embedded in organic matrices.Enterobacter sakazakii causes meningitis (7, 19), sepsis (47), bacteremia (40), and necrotizing enterocolitis (51) in preterm neonates and infants. Powdered infant formula has been implicated as a source of E. sakazakii in outbreaks of infections (2,5,6,21,39,40,47,51). In surveys done to determine the presence of E. sakazakii in powdered infant formula, the organism was detected in 2.4 to 14.2% of the products tested (22,38).The presence of E. sakazakii on the surface of utensils and equipment used for infant formula preparation has been reported to occur in clinical settings where neonatal infections have been documented (2,10,40,47). The ability of bacteria to form biofilms on abiotic surfaces (22,27,30) raises the possibility that infections may occur following cross-contamination of freshly prepared infant formulas upon contact with soiled surfaces in formula preparation areas in hospitals, day-care centers, food service kitchens, and the home. Food-borne pathogens, e.g., Escherichia coli O157:H7 and Listeria monocytogenes, and spoilage bacteria such as Pseudomonas spp. have enhanced resistance to antibiotics or sanitizers when cells are in biofilms (13,17,18,43), thus increasing the potential for survival on these surfaces.Surface disinfection is routinely carried out in formula preparation areas in hospitals, food service kitchens, and day-care centers by applying liquid chemical disinfectants to food contact and non-food contact surfaces. The microbicidal activity of commercial surface cleaners and disinfectants is largely based on quaternary ammonium compounds, phenolic compounds, organic acids, alcohols, chlorine, and iodophors. Various commercial hard...

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