Fifty percent lethal dose (LD₅₀) determinations of mice inoculated at different gestational stages.

<p>Striped bars indicate the log₁₀ colony forming units (cfu) required to produce death in 50% of the inoculated animals. Mice were inoculated and observed as described in the text. At least three groups of animals with three different listerial doses were used to determine the LD₅₀. Groups consisted of not fewer than 4 mice. Error bars denote standard error of the mean. Probit analysis was used to determine statistical differences between groups. Asterisks denote values that were statistically different from the nongravid group (denoted by zero gestational days).