Abstract
Enterobacter sakazakii
is an emerging pathogen that has been associated with outbreaks of necrotizing enterocolitis (NEC) as well as infant sepsis and meningitis. Our previous studies demonstrated that
E. sakazakii
induces NEC in a newborn rat model by inducing enterocyte apoptosis. However, the mechanisms responsible for enterocyte apoptosis are not known. Here we demonstrate that
E. sakazakii
induces significant production of nitric oxide (NO) in rat intestinal epithelial cells (IEC-6) upon infection. The elevated production of NO, which is due to increased expression of inducible NO synthase, is responsible for apoptosis of IEC-6 cells. Notably, pretreatment of IEC-6 cells with
Lactobacillus bulgaricus
(ATCC 12278) attenuated the upregulation of NO production and thereby protected the cells from
E. sakazakii
-induced apoptosis. Furthermore, pretreatment with
L. bulgaricus
promoted the integrity of enterocytes both in vitro and in the infant rat model of NEC, even after challenge with
E. sakazakii
. Infection of IEC-6 cells with
E. sakazakii
upregulated several genes related to apoptosis, cytokine production, and various signaling pathways, as demonstrated by rat gene array analysis, and this upregulation was subdued by pretreatment with
L. bulgaricus
. In agreement with these data,
L. bulgaricus
pretreatment protected newborn rats infected with
E. sakazakii
from developing NEC, resulting in improved survival.
