Variation in the infectivity of Listeria monocytogenes isolates following intragastric inoculation of mice

Abstract

The infectivities of 66 Listeria monocytogenes isolates were assessed by intragastric inoculation of mice. Eight were poorly infective. Serovars 4b and 1/2 were more infective than serovars 3 and 4nonb. A noninfective isolate was cleared more rapidly from the cecum than were infective isolates, suggesting that survival in the gut may relate to infectivity.

FIG. 1

Viable bacterial counts in spleen (a), liver (b), and cecal contents (c) of mice inoculated i.g. with 2 × 10⁹ CFU of selected isolates of L. monocytogenes. Each point represents the mean of the log₁₀s of the viable count per gram of tissue for three mice on days 1 to 4 and two mice on days 5 and 7.

FIG. 2

Infectivities of 66 isolates of L. monocytogenes, grouped by serovar, assessed by viable bacterial counts in spleen (a) and liver (b) 3 days following i.g. inoculation with 2 × 10⁹ CFU. Results are expressed as the means of the log₁₀s of the viable counts per organ from three mice per isolate grouped in 1-log intervals.

FIG. 3

The average (mean) infectivity of the different serovars of L. monocytogenes assessed by viable bacterial counts in spleen (a) and liver (b) 3 days following i.g. inoculation with 2 × 10⁹ CFU. The graph shows the mean of results from each serovar expressed as log₁₀ CFU per organ ± 95% confidence interval (error bars).