Early life supply of competitive exclusion products reduces colonization of Extended Spectrum Beta-Lactamase producing Escherichia coli in broilers

Broilers are an important reservoir of ESBL/pAmpC-producing bacteria. In previous studies a single supply of a competitive exclusion (CE) product before challenge with a high dose of ESBL/pAmpC-producing E. coli led to reduced colonization, excretion and transmission, but could not prevent colonization. The hypothesized mechanism is competition; therefore in this study the effect of a prolonged supply of CE products on colonization, excretion and transmission of ESBL-producing E. coli after challenge with a low dose at day 0 or day 5 was investigated. Day-old broilers (Ross 308) (n=220) were housed in isolators. Two CE products, containing unselected fermented intestinal bacteria (CEP) or a selection of pre- and probiotics (SYN), were supplied in drinking water from day 0 to 14. At day 0 or day 5 broilers were challenged with 0.5 mL with 101 or 102 cfu/mL E. coli encoding the beta–lactamase gene blaCTX-M-1 on an IncI plasmid (CTX-M-1-E. coli). Presence and concentration of CTX-M-1-E. coli was determined using cloacal swabs (day 0-14, 16, 19, 21) and cecal content (day 21). Cox proportional hazard model and a mixed linear regression model were used to determine the effect of the intervention on colonization and excretion (log10 cfu/g). When challenged at day of hatch, no effect of CEP was observed. When challenged at day 5, both CEP and SYN led to a prevention of colonization with CTX-M-1-E. coli in some isolators. In the remaining isolators, we observed reduced time until colonization (HR between 3.71 ×10-3 and 3.11), excretion (up to -1.60 log10 cfu/g) and cecal content (up to -2.80 log10 cfu/g) and a 1.5 to 3-fold reduction in transmission rate. Colonization after a low dose challenge with ESBL-producing E. coli can be prevented by CE products. However, if at least one bird is colonized it spreads through the whole flock. Prolonged supply of CE products provided shortly after hatch, may be applicable as an intervention to reduce prevalence of ESBL/pAmpC-producing bacteria in the broiler production chain.