Methods for Recovery of Campylobacter jejuni from Foods

Abstract

The triangular relationship between Campylobacter jejuni, foods and disease in humans has been well-documented. Many studies have revealed that C. jejuni causes at least as many cases of human gastroenteritis as does Salmonella sp. Foods are an important vehicle in human infection, and raw milk is most frequently implicated. Other animal products also serve as potential sources of infection. C. jejuni has been found on the carcasses of poultry and other domestic animals throughout the world. The organism is microaerophilic and various methods for establishing appropriate growth conditions, such as the Fortner principle, atmosphere replacement and adding of supplements to encourage growth of C. jejuni, are available. Methods developed for use in clinical laboratories lack the necessary sensitivity and selectivity, and therefore have limited use in detecting small numbers of C. jejuni in foods. In one enrichment method for detecting C. jejuni in foods, washings are filtered and centrifuged, the sediment is suspended in the enrichment broth and the suspension is incubated under a constant gas flow at reduced oxygen levels. Following incubation enrichment broth is filtered and plated onto selective media. In another recently developed method, food samples are directly added to an enrichment broth with antibiotics and incubated under a microaerobic atmosphere before selective plating. Butzler's, Skirrow's and Campy-BAP selective media use several antibiotics to which C. jejuni is resistant. The plates are supplemented with horse or sheep blood, depending upon the specific formulation. The optimum temperature for growth of C. jejuni, about 42°C, may also be used for selection. It is now possible to recover 0.1 to 1 cell of C. jejuni per 10 to 25 g of food sample from among 106 to 109 indigenous bacteria. After a characteristic colony is isolated, the key criteria for presumptive identification of C. jejuni by phase-contrast microscopy are darting, corkscrew motion and a comma to spiral shape.