Growth of L. monocytogenes strain F2365 on ready-to-eat turkey meat does not enhance gastrointestinal listeriosis in intragastrically inoculated A/J mice

Abstract

There have been significant outbreaks of listeriosis associated with consumption of contaminated ready-to-eat (RTE) turkey meat products. In this study, we investigated whether growth on RTE deli turkey meat sends environmental signals to listerial cells that makes them more virulent in the gastrointestinal tract of mice. L. Listeria monocytogenes strain F2365 grew from a starting inoculum of 10(3) CFU/mL to final numbers of 10(8)-10(9) CFU/mL (within 12 days at 10 degrees C) when inoculated onto sliced processed, or whole muscle, turkey breast, or into emulsified whole turkey breast. We did not observe any difference in the numbers of CFU recovered from the spleens and livers of A/J mice inoculated intragastrically with L. monocytogenes grown on sliced turkey meat, in emulsified turkey meat, or in brain heart infusion broth. These results suggest that growth on RTE sliced deli turkey, or in RTE emulsified deli turkey, does not enhance the ability of L. monocytogenes F2365 to cause gastrointestinal listeriosis in intragastrically challenged A/J mice.

Fig. 1

Growth curves of L. monocytogenes F2365 inoculated (10³ CFU/ml) in BHI broth, onto RTE sliced processed deli turkey meat, or into emulsified whole muscle turkey breast meat and then incubated at 10 °C for 12 days. Samples were aseptically removed at daily intervals and plated on blood agar or modified Oxford agar. Results are presented as the mean ± S.E.M. from one representative experiment of 3 separate experiments performed (two replicates for each growth condition).

Fig. 2

L. monocytogenes F2365 cells grown in BHI broth (closed bars) or on sliced whole muscle turkey breast (open bars) for 12 days at 10 °C do not differ in their ability to infect A/J mice when given intragastrically. Results are the mean ± S.E.M. of two independent experiments (n = 12 per experimental group). The limit of detection for the gallbladder was 10³ CFU per gram and for all other tissues was 10¹ CFU per g tissue. Tissues having no detectable L. monocytogenes colonies were given a value of 2.95 or 0.95 log¹⁰ CFU per g tissue, respectively.

Fig. 3

L. monocytogenes F2365 cells grown in BHI broth (closed bars) or in emulsified whole muscle turkey (open bars) for 12 days at 10 °C do not differ in their ability to infect A/J mice when given intragastrically. Results are the mean ± S.E.M. of three independent experiments (n = 18 per experimental group). The limit of detection for the gallbladder was 10³ CFU per gram and for all other tissues was 10¹ CFU per g tissue. Tissues having no detectable L. monocytogenes colonies were given a value of 2.95 or 0.95 log₁₀ CFU per g tissue, respectively.

Fig. 4

L. monocytogenes F2365 cells grown in BHI (closed bars) or on sliced processed turkey meat (open bars) for 12 days at 10 °C do not differ in their ability to infect A/J mice when given intragastrically. Results are the mean ± S.E.M. of two independent experiments (n = 12 per experimental group). The limit of detection for the gallbladder was 10³ CFU per gram and for all other tissues was 10¹ CFU per g tissue. Tissues having no detectable L. monocytogenes colonies were given a value of 2.95 or 0.95 log₁₀ CFU per g tissue, respectively.