Table 1 Number of ESBL/ AmpC Escherichia coli (EEC) challenge organisms (mean log₁₀ cfu/g of 4 birds) in caecal contents of specific pathogen free White Leghorn chickens pre-treated with a competitive exclusion (CE) culture on day 1 of life or untreated controls exposed to seeder birds infected with EEC 1478 N (SHV-12) or EEC 1479 N (CMY-2) at 2 days of life (5 contact birds/ 1 seeder bird) (experiment 1)

1

20 contact birds pre-treated with a CE culture

20 contact birds untreated

20 contact birds pre-treated with a CE culture

20 contact birds untreated

2

Addition of 4 seeder birds infected with EEC 1478 N (10⁵ cfu/ bird)

Addition of 4 seeder birds infected with EEC 1478 N (10⁵ cfu/ bird)

Addition of 4 seeder birds infected with EEC 1479 N (10⁵ cfu/ bird)

Addition of 4 seeder birds infected with EEC 1479 N (10⁵ cfu/ bird)

Caecal contents

Caecal contents

Caecal contents

Caecal contents

9

6.2^a

8.7

5.7^b

8.8

16

5.7^a

8.5

4.0^b

8.6

23

3.2^a

8.3

3.0^b

8.6

30

3.0^a

8.2

2.9^b

8.6

37

2.2^a

7.8

2.4^b

8.5