A single intraperitoneal injection of
Lactobacillus casei YIT 0003 into normal or dexamethasone-treated mice led to nonspecific resistance against intraperitoneal challenge with lethal doses of
Pseudomonas aeruginosa PAO 3047. The enhanced resistance was retained for 14 days (
P<0.05) after injection with living
L. casei. In contrast, the statistically significant duration of the enhanced resistance in mice treated intraperitoneally with living
L. acidophilus YIT 0075 was only 5 days. The
in vivo killing activity of peritoneal exudate cells (PECs) against
P. aeruginosa 5 and 7 days after intraperitoneal injection of living
L. casei was significantly higher than in the case of PECs elicited by
L. acidophilus. In the case of intravenous injection of heat-killed
L. casei before intraperitoneal challenge with
P. aeruginosa, there were no survivors in the late period after administration of
L. casei. A high correlation existed between the patterns of
in vivo killing of
P. aeruginosa by PECs and survival rate of mice injected intravenously with heat-killed
L. casei. The reduced
in vivo killing activity of PECs from dexamethasone-treated mice against
P. aeruginosa infection was also augmented by the intraperitoneal injection of heat-killed
L. casei. These results indicate that
L. casei possesses a resistance-enhancing capacity against
P. aeruginosa infection
in vivo. Differences in the duration of the enhanced resistance caused by
L. casei and by
L. acidophilus may be due to differences in chemical composition and/or physicochemical properties of the cell walls of the two kinds of bacteria.
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