The abundant free-living amoeba, Acanthamoeba polyphaga, increases the survival of Campylobacter jejuni in milk and orange juice

Abstract

Background

Campylobacter jejuni is a common cause of human bacterial diarrhea in most parts of the world. Most C. jejuni infections are acquired from contaminated poultry, milk, and water. Due to health care costs and human suffering, it is important to identify all possible sources of infection. Unpasteurized milk has been associated with several outbreaks of C. jejuni infection. Campylobacter has been identified on fresh fruit, and other gastrointestinal pathogens such as Salmonella, E. coli O157:H7 and Cryptosporidium have been involved in fruit juice outbreaks. C. jejuni is sensitive to the acidic environment of fruit juice, but co-cultures with the amoeba, Acanthamoeba polyphaga, have previously been shown to protect C. jejuni at low pH.

Methods

To study the influence of A. polyphaga on the survival of C. jejuni in milk and juice, the bacteria were incubated in the two products at room temperature and at 4°C with the following treatments: A) C. jejuni preincubated with A. polyphaga before the addition of product, B) C. jejuni mixed with A. polyphaga after the addition of product, and C) C. jejuni in product without A. polyphaga. Bacterial survival was assessed by colony counts on blood agar plates.

Results

Co-culture with A. polyphaga prolonged the C. jejuni survival both in milk and juice. The effect of co-culture was most pronounced in juice stored at room temperature. On the other hand, A. polyphaga did not have any effect on C. jejuni survival during pasteurization of milk or orange juice, indicating that this is a good method for eliminating C. jejuni in these products.

Conclusion

Amoebae-associated C. jejuni in milk and juice might cause C. jejuni infections.

• unpasteurized milk
• fruit juice
• C. jejuni infection
• co-culture
• Campylobacter survival
• gastrointestinal pathogens

Acknowledgements

The authors thank Dr. Alexis Avril for valuable comments regarding the statistical analysis. The study was financially supported by the Swedish Research Council FORMAS (grant numbers: 2220-8779-120, 221-2012-1442).