Abstract
In 2014 the prevalence of ESBL producing E. coli found on broiler carcasses in Dutch slaughterhouses was 66 percent, the ESBLs found in humans and broilers show higher similarities over the last few years. Therefore it is presumed that ESBL transmission from broilers to humans can occur via the
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food chain, through consumption of contaminated meat. Consequently decreasing ESBLs in the broiler production chain can have an important impact on public health. One of the possible routes for the spread of ESBLs in the broiler production chain is vertical transmission. The aim of this study was to investigate vertical transmission as a possible route for the spread of ESBL producing E. coli in the broiler production chain by monitoring broilers offspring from broiler breeders tested positive for ESBLs.
For this experiment, 480 eggs were taken from two different broiler breeder flocks from a Dutch poultry farm. Flock 1 was 60 weeks of age and had been ESBL negative during the entire rearing and laying period. Flock 2 tested positive for ESBLs with a prevalence of 90 percent in the first week of the rearing period and was divided into flock 2a and 2b. During egg collection, at week 34 of age flock 2a was ESBL negative according to individual cloacal swabs, but the environment was still ESBL positive. In flock 2b both environment and 6% of the broiler breeders were tested ESBL positive. The eggs were transported to the faculty of Veterinary Medicine in Utrecht and were incubated separately per group (n=120 per group). The remaining eggs were taken for further analysis for the presence of ESBLs. After hatching the 3 groups of broilers were checked for the presence of ESBLs during the first 3 weeks by cloacal swabs, boot sock sampling of the litter and at the end of the experiment post mortem examination was done to collect the caeca for bacteriological examination.
None of the samples tested positive for the presence of ESBL producing E. coli, so vertical transmission of ESBL producing E. coli was not detected in this experiment. However it cannot be concluded that vertical transmission of ESBLs is not a possible route for the spread of ESBLs in the broiler production chain. The prevalence of the ESBLs found in the broiler breeders may have been of insignificant quantity and disinfection of the eggs before incubation may have diminished the opportunity for apparent vertical transmission. Also the colonization of ESBL producing E. coli at gut level could play a role in the appearance of the vertical transmission of ESBLs. More research is needed to determine whether vertical transmission is a possible transmission route of ESBL producing E. coli in the broiler production chain.
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