Campylobacter contamination level in houseflies after exposure to materials containing Campylobacter

Although houseflies have been found to carry Campylobacter jejuni, little is known about the quantitative campylobacter level in naturally contaminated houseflies and their ability to contaminate surfaces. This study aimed to elucidate how houseflies’ previous exposure to campylobacter-contaminated material (faeces or liquid) for 1 or 4 h affects the acquired campylobacter level in houseflies and their contamination potential. Cups of 250 ml were added 5 g of chicken faeces or 1 ml liquid and spiked with approximately 3, 4, 5 or 7 log10 cfu C. jejuni. Sixteen houseflies were added to each cup. After 1 h of exposure, four houseflies were removed from the cup for enumeration of campylobacter in each fly by plate spreading. Another four houseflies were transferred onto Abeyta-Hunt-Bark (AHB) agar plates (9 cm) to assess possible contamination of surfaces. After 1 h on the AHB plate, each fly was tested for level of campylobacter. This procedure was repeated after approx. 4 h of exposure for the remaining eight houseflies. The C. jejuni acquisition in houseflies increased with exposure dose and was higher after liquid exposure compared with faeces exposure, while there was no significant effect of exposure time (1 vs 4 h). For faeces, 90.0% (n=80), 48.4% (n=64), 6.3% (n=48) and 0% (n=16) of houseflies were campylobacter-positive when exposed to 7, 5, 4, and 3 log10 cfu with a mean (±SE) of 2.0±0.1, 0.8±0.1, 0.3±0.0 and 0 log10 cfu recovered per campylobacter-positive fly, respectively. For liquid, 95.7% (n=47), 91.4% (n=47), 20.8% (n=48) and 6.3% (n=16) of houseflies were campylobacter-positive with a mean of 3.3±0.2, 2.0±0.1, 0.8±0.2 and 0.3±0.0 log10 cfu. The surface of the AHB plates was only contaminated by houseflies previously exposed to >4 log10, but the C. jejuni number found on the AHB surface did not correlate with the number found in the corresponding fly.