The objective of this study was to examine the effect of chronic exposure to cadmium and zinc on the mice resistance to experimental Listeria monocytogenes infection.
Materials and methods: At the day beginning of experiment outbred mice were injected with suspension of bacteria and 8 weeks were given the following oral intake treatment: control group (n=28) deionized drinking water, Cd- group (n=37) water containing CdCl2 10 mg/l and Cd+Zn- group (n=33) water containing CdCl2 10 mg/l and ZnSO4 100 mg/l. The delayed type hypersensitivity was evaluated by the inflammatory response during so-called "foot" test. Listerial proteins solution was injected under plantare of lower aponeurosis of rear foot of experimental animals. Survival of L. monocytogenes in organs of experimental animals was evaluated by the presence of bacteria colonies after 30 days incubation of livers homogenates in broth medium at +4 degrees C and inoculation on CASO-agar. Kidneys, liver and spleen were used for metals analysis. Differences were significant if the P value was below 0.05.
Results: Chronic exposure to Cd or to Cd with Zn for 8 weeks caused influence on survival of mice: Cd- and Cd+Zn groups mice died more rapidly than control group ones. Bacterial growth in organs was observed for all groups until fourth week. From sixth-week, control and Cd+Zn- group's mice more rapidly eliminated bacteria from organs, demonstrating that Zn- treated mice were more resistant to listerial infection than Cd- intoxicated ones. On the other hand, mice from Cd+Zn- group had significantly decreased spleen index (up to 74%, p<0.01) as compared to control group. Chronic poisoning of mice with low doses cadmium and zinc during infection significantly affected (p<0.05) their growth rate from fourth week in both experimental groups. Cadmium and zinc insignificantly decreased the delayed type hypersensitivity response to L. monocytogenes allergens in Cd+Zn- group of mice, and no differences were observed in Cd- group, as compared with control group.
Conclusions: 1. Cadmium-exposed mice are more susceptible to Listeria monocytogenes and to other opportunistic infections than not intoxicated mice. 2. Zinc significantly reduces the negative effect of cadmium on the antimicrobial defense of mice. 3. Cadmium and zinc no significantly decrease the delayed type hypersensitivity response to L. monocytogenes allergens as compared with control.