Table 1. Distribution of minimum inhibitory concentrations (mg/L) for Escherichia coli isolates (n = 296) from faeces of Australian layer chickens.

The percentage of resistance based on ECOFF breakpoints (non-wild type) and clinical breakpoints (clinical resistance) are presented on the right-hand side (Percentage results were rounded to one decimal place). Vertical bars indicate position of ECOFF breakpoint.

	Minimum Inhibitory Concentration (μg/ml)
drug	0.016	0.03	0.06	0.13	0.25	0.5	1	2	4	8	16	32	64	128	256	nw*	nw_ci^	cr#	cr_ci^
Amoxicillin-Clavulanate							2.4	8.4	39.2	40.9	6.4		2.7			9.1	6.1,13	2.7	1.2,5.3
Ampicillin							.7	10.5	54.1	18.6	3.7	3	9.5			16.2	12.2,20.9	12.5	9,16.8
Cefoxitin							3.4	43.9	40.2	11.1	1.4					0	0,1.2	0.0	0,1.2
Ceftiofur				20.3	60.1	18.6	1									0	0,1.2	0.0	0,1.2
Ceftriaxone					95.9	3.7	.3									.	.	0.0	0,1.2
Chloramphenicol								1	24.3	67.9	6.8					0	0,1.2	0.0	0,1.2
Ciprofloxacin	97	.3		1.4	1.4											2.7	1.2,5.3	0.0	0,1.2
Colistin				5.4	80.1	13.5	1									0	0,1.2	0.0	0,1.2
Florfenicol									4.4	49.7	43.6	2.4				2.4	1,4.8	45.9	40.2,51.8
Gentamicin					36.5	44.3	13.9	4.4	.7			.3				1	.2,2.9	0.3	0,1.9
Streptomycin								33.8	50.3	9.8	1.4	1.4	2	1.4		4.7	2.6,7.8	.	.
Tetracycline									59.8	2.4	2	2	33.8			37.8	32.3,43.6	37.8	32.3,43.6
Trimethoprim/Sulfamethoxazole				87.8	1.7	1	.3			9.1						9.5	6.4,13.4	9.1	6.1,13

*nw—percent non-wildtype based on ECOFF breakpoints,

^#cr—percent clinically resistant based on CLSI guidelines,

^ci—95% confidence interval.

Grey shading represents the concentration range tested. Values outside of the shaded area indicate isolate growth at all concentrations tested.