Characteristics of Escherichia coli Isolated from Bovine Mastitis Exposed to Subminimum Inhibitory Concentrations of Cefalotin or Ceftazidime

Table 2

Minimal inhibitory concentrations of cefalotin and ceftazidime against Escherichia coli isolates.

		MIC of E. coli isolates (μg/mL)
Isolate	Antimicrobial	Parent type	-1	-2	-3	-4	-5	-6	-7	-8	-9
E4	Cefalotin†	4	8	32	80	240	240	320	320	320	320
	Ceftazidime‡	0.125	0.25	2	4	16	16	32	32	64	128
E11	Cefalotin	0.5	2	16	32
	Ceftazidime	1	4	8	8	16	32	32	64	128	128
E21	Cefalotin	2	8	16	16
	Ceftazidime	0.5	1	4	4	8	16	16	32	32	64

No mark: susceptible or intermediate to cefalotin or ceftazidime; #: resistant to cefalotin or ceftazidime. Breakpoints for cefalotin were as follows: susceptible ⩽ 8 μg/mL, intermediate 16 μg/mL, and resistant ⩾ 32 μg/mL. Breakpoints for ceftazidime were as follows: susceptible ⩽ 2 μg/mL, intermediate 4 μg/mL, and resistant ⩾ 8 μg/mL.
Escherichia coli isolates at various generations that were induced by cefalotin or ceftazidime.
†MIC values of cefalotin were determined for E. coli isolates induced by cefalotin.
‡MIC values of ceftazidime were determined for E. coli isolates induced by ceftazidime.