Internalization Rates and Survival of Campylobacter jejuni by Acanthamoeba castellanii Varies by Strains of Campylobacter

Introduction: Campylobacter jejuni is one of the leading causes of foodborne illness in the U.S.  Studies have shown that C. jejuni is able to survive phagocytosis by amoeba such as Acanthamoeba castellanii and reside intracellularly.  Once inside of A. castellanii, C. jejuni has been shown to be protected from environmental factors including oxygen, pH, and chemicals (i.e., chlorine).  This protection by amoebae may aid in the persistence of C. jejuni in the food industry.

Purpose: We investigated internalization rates among different C. jejuni strains into A. castellanii to determine if there is variation among C. jejuni strains. 

Methods: C. jejuni strains were co-incubated 2 hours with A. castellanii to allow internalization. Washes with saline and gentamicin were used to remove extracellular and attached bacteria and Triton X-100 was used to lyse A. castellanii and release intracellular C. jejuni.  Three trials were performed for each strain with triplicate samples per trial.  Rates of internalization were determined by dividing the averages of total CFU C. jejuni recovered by total A. castellanii recovered.

Results: C. jejuni NCTC 11168 was employed as a reference strain for each experiment.  C. jejuni strains 81-176 and NCTC 11168 ΔflgK showed a 2 log decrease in rate of internalization and 81-176 ΔCj0596 showed ~0.5 log increase in internalization into A. castellanii compared to the reference strain.   Strains ATCC 43502 and  81116 showed a negative rate of internalization suggesting that these strains are not internalized or do not survive internalization.

Significance: The results of this study indicate that the rate of internalization (and therefore protection) of C. jejuni by A. castellanii is variable among strains.  If internalization and protection from environmental stresses by A. castellanii is variable this may have implications for understanding survival of Campylobacter in poultry processing where amoebae have been isolated in previous studies.