TABLE 1.

Cephalosporinase activity and susceptibilities of test strains

Strain	Cephalosporinase activitya		MIC (μg/ml)
	Uninduced	Induced	Cefepime	Ceftazidime	Cefotaxime	Aztreonam	Aztreonam + cefepimeb	Aztreonam + ceftazidimeb
P. aeruginosa 164	5	87	8	4	32	8	8/4	4/2
P. aeruginosa 164PD	38	429	16	32	>128	16	32/16	32/16
P. aeruginosa 164FD	1,640	1,810	128	>128	>128	>128	128/64	128/64
P. aeruginosa 113M	70	275	16	32	>128	16	32/16	32/16
P. aeruginosa 111M	142	169	16	32	>128	16	32/16	32/16
P. aeruginosa GB57	971	1,040	64	>128	>128	128	128/64	128/64
P. aeruginosa GB66	971	1,150	64	>128	>128	>128	128/64	128/64
P. aeruginosa GB3	1,270	1,290	64	64	>128	64	128/64	128/64

^aCephalosporinase activity (nanomoles of cephalothin hydrolyzed per minute per milligram of protein) in sonic extracts of logarithmic-phase cultures treated for 2 h with 25 μg of cefoxitin per ml (induced). Uninduced cultures were supplemented with drug-free broth and were incubated for a similar 2-h period. 

^bTested at a ratio of 2 parts aztreonam to 1 part cefepime or ceftazidime.