TABLE 2.

Comparison of the strength of the − 11 mutated ampC promoter from E. coli strain 99004202 with that of the ampC promoter from strain ATCC 25922 and that from the mutant 96010266M (3)

Plasmid used to transform JM109 cells	Chloramphenicol MIC (mg/liter)	CAT level (pg/μg)a
None	8	4 ± 0.5
pKK232-8b	8	4 ± 0.5
pKK232-8 (ATCC 25922)c	32	120 ± 32
pKK232-8 (99004202)d	512	761 ± 41
pKK232-8 (96010266M)e	32	95 ± 8

^aMean ± standard deviation of three determinations of CAT concentration.

^bpKK232-8 without any insert.

^cpKK232-8 containing the ampC promoter from strain ATCC 25922 (low-level AmpC producer).

^dpKK232-8 containing the ampC promoter from strain 99004202 (moderate-level AmpC producer).

^epKK232-8 containing the ampC promoter from the mutant 96010266M (3).