IDENTIFICATION OF PROTEINS INVOLVED IN INFECTIVITY AND ENTEROTOXIN PRODUCTION IN ENTEROBACTER SAKAZAKII

Enterobacter sakazakii is a gram-negative rod bacterium that was formerly known as "yellow-pigmented Enterobacter cloacae" until 1980. It is an emerging opportunistic pathogen associated with bacterial meningitis in immunocompromised neonates who ingested contaminated powdered infant formula. In several E. sakazakii-related outbreaks and sporadic cases, powdered infant formula was epidemiologically or microbiologically established as the source of infection. The International Commission on Microbiological Specifications for Foods has ranked E. sakazakii as a "severe hazard for restricted populations." However, the organism was isolated at very low levels from commercial powdered infant formula and dry environmental samples collected from infant formula factories. In most cases, the contamination did not exceed 1 cfu per 100 g. Progress in understanding the epidemiology of E. sakazakii outbreaks and instituting effective control measures has been poor to date. To clarify the mechanisms involved in infectivity and enterotoxin production, we performed two-dimensional gel electrophoresis (2-DE) coupled with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and isotope-coded affinity tags (ICATs)-LC -MS to identify and quantify differences in protein expression between the E. sakazakii strains. We found 23 spots in 2-DE and 37 proteins in ICAT analysis that were differentially expressed in E. sakazakii. These two methods gave us closely related but different information, suggesting that the two methods are complementary or at least supplementary.