Effects of growth temperature on the ingestion and killing of clinical isolates of Listeria monocytogenes by human neutrophils

Abstract

In this study, we compared three human isolates (F5380, Scott A, and Murray B) and one laboratory strain (EGD) of Listeria monocytogenes for their resistance to ingestion and killing by human neutrophils. We observed no substantial difference in killing among these strains when they were grown at 37°C. Because it is likely that listerial growth occurs at lower temperatures during food-borne outbreaks of listeriosis, we also compared these strains after they were grown at 22 and 4°C. A general reduction in the ability of human neutrophils to kili L. monocytogenes was observed as the temperature at which the listeriae were grown decreased. Growth at 4°C significantly decreased the killing of ail four strains of L. monocytogenes by human neutrophils; two strains (EGD and F5380) were more resistant to killing than were the other two strains (Scott A and Murray B). No obvious relationship was noted between the chemiluminescence response of neutrophils to opsonized listeriae and the ability of the neutrophils to kill listeriae in vitro. Growth at 4°C, however, significantly increased the resistance of L. monocytogenes to killing by hydrogen peroxide.

Listeria monocytogenes, a food-borne pathogen.

“…Czuprynski et al 85, on the other hand, demonstrated the ability of bovine phagocytes (blood polymorphonuclear leukocytes, monocytes, and milk leucocytes) to ingest the organism, produce an oxidative response, and kill the intracellular listeriae. When tested with human neutrophils, L. monocytogenes F5380, Scott A, Murray B, and EGD were more resistant to killing when grown at 4 than at 37°C (395). This decreased killing did not appear to be related to poor ingestion by the neutrophils.…”