TABLE 2.

MIC values of different β-lactams and β-lactamase genes detected in the 13 E. coli strains obtained from fecal samples of healthy chickens with diminished susceptibility or resistance to broad-spectrum cephalosporins

E. coli isolate	MIC (μg/ml)										ESBL test resultb	Plasmidic β-lactamase gene(s) detected	Mutations in the promoter-attenuator of the ampC gene
	AMP	TIC	AMC	CFZ	FOX	CAZ	CTX	CRO	IMP	ATM
A3SAEC 269-271	>256	>128	4	>128	8	1	64	128	0.125	2	+	blaTEM-1b + blaCTX-M-14	No mutations
A3SZEC 377-379	>256	>128	4	>128	4	1	64	128	0.125	2	+	blaCTX-M-14	No mutations
A3SZEC 443-445	>256	>128	8	>128	4	≤0.5	32	128	≤0.06	2	+	blaCTX-M-14	No mutations
A3YEEC 209-211	>256	>128	4	>128	4	1	64	128	≤0.06	4	+	blaCTX-M-14	−18, −1, +58
A3SZEC 431-433	>256	>128	8	>128	4	≤0.5	8	16	0.125	2	+	blaTEM-1b + blaCTX-M-9	−28, +58
A3AGEC 425-427	>256	>128	8	32	4	16	4	4	0.125	32	+	blaTEM-1b + blaSHV-12	No mutations
A3SZEC 368-370	>256	>128	8	32	8	16	4	4	0.125	32	+	blaTEM-1b + blaSHV-12	+22, +26, +27, +32
A3LEEC 064-066	>256	>128	4	32	8	32	8	8	0.125	32	+	blaSHV-12	No mutations
A3YEEC 296-298	>256	>128	32	>128	64	8	8	16	0.125	8	−	blaTEM-1b + blaCMY-2	No mutations
A3AAEC 031-033	256	64	64	>128	64	2	8	16	0.125	4	−	blaCMY-2	No mutations
A3SAEC 239-241	>256	>128	32	32	16	2	1	0.5	0.125	2	−	blaTEM-1b	−42, −18, −1, +58
A3AVEC 404-406	256	32	64	32	16	2	2	0.5	0.125	2	−	No bla genes detected	−42, −18, −1, +58
A3COEC 551-553	128	32	32	16	16	2	1	0.5	0.125	2	−	No bla genes detected	−42, −18, −1, +58

^aAMP: ampicillin; TIC: ticarcillin; AMC: amoxicillin-clavulanic acid; CFZ: cefazolin; FOX: cefoxitin; CAZ: ceftazidime; CTX: cefotaxime; CRO: ceftriaxone; IMP: imipenem; ATM: aztreonam.

^b+, positive; −, negative.