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

Table 5

Results of a linear mixed regression model for log endotoxin release (log of EU/mL) by Escherichia coli after exposure to cefalotin (CF) or ceftazidime (CAZ).

Parameter	Estimate	SEM	P-value
Parent isolates (Ref.)	6.07	0.11	<0.001
CAZ	0.50	5.01 x 10^−3	<0.001
CF	0.02	5.01 x 10^−3	0.699
Interactions†
CAZ x generation	3.78 x 10^−4	5.23 x 10^−3	0.942
CF x generation	1.39 x 10^−3	5.23 x 10^−3	0.791
Time (h)	1.60	0.02	<0.001
Time^2 (h^2)	-0.16	5.39 x 10^−3	<0.001
Time^3 (h^3)	0.01	3.54 x 10^−4	<0.001
Between-replicate variance	0.03	0.16

Endotoxin release was measured at various time points (2, 4, 6, 8, and 10 h) and resistance was induced over varying numbers of generations.
Baseline to which other samples were compared was a parent isolate (generation 0)
†Interactions were not created with the parent isolate as there was only 1 generation