Competitive exclusion: A tool to combat extended-spectrum β-lactamase-producing Escherichia coli strains in chickens

Apart from effective hygiene regimes in poultry houses, measures to increase the resistance of birds against intestinal colonisation with EEC (= extended-spectrum β-lactamases [ESBL] and AmpC-type [AmpC] beta-lactamses producing Escherichia coli) might be one tool to reduce the risk of transferring these organisms from broilers via poultry meat to humans. The study aimed to gain detailed information on the efficacy of a competitive exclusion culture (CE culture) against EEC exposure in very young chicks. Administration of only 10⁴ cfu/bird on day 2 of life with seven EEC strains (different ESBL and AmpC genes) induced a high and rapid intestinal colonisation in untreated chicks which lasted until an age of 5 weeks. Pretreatment of the birds with a CE culture resulted in a relevant reduction (about 4.0 log₁₀ units) of the different EEC strains. A considerable protective effect (reduction of 2.0 log₁₀ units) by the CE culture could be detected after exposure of the chicks with very high doses of 10⁶ to 10⁸ cfu/bird. Invasion of the liver by EEC organisms was completely prevented by the CE culture even in case of very high challenge doses. The CE culture of undefined composition used here resulted in a substantial decrease of caecal colonisation of EEC strains in young chickens over a lifetime of broilers. Because of the different protective effects against the single EEC strains, modifications in the composition of undefined CE cultures or the development of defined cultures effective against EEC might improve the efficacy of gut flora preparations.