TABLE 1.

Characterization of β-lactamases of M. catarrhalis isolates obtained during multicenter U.S. national surveillance studies conducted from 1994 to 1995 and from 1997 to 1998

Study time and ampicillin MIC (μg/ml)	Total no. (%) of β-lactamase-positive isolates in study	No. of isolates characterized by IEF	No. (%) of BRO-1-producing isolatesa	No. (%) of BRO-2-producing isolatesa
1994 to 1995
0.06	2 (0.3)	2	1 (50.0)	1 (50.0)
0.12	6 (1.0)	6	1 (16.7)	5 (83.3)
0.25	21 (3.6)	21	19 (90.5)	2 (9.5)
0.5	27 (4.7)	27	24 (88.9)	3 (11.1)
1	60 (10.4)	60	59 (98.3)	1 (1.7)
2	113 (19.6)	48	48 (100)
4	162 (28.1)	10	10 (100)
8	118 (20.5)	10	10 (100)
16	59 (10.2)	10	10 (100)
32	7 (1.2)	7	7 (100)
>32	1 (0.2)	1	1 (100)
Total	576	202	190	12
1997 to 1998
0.06	5 (1.0)	5		5 (100)
0.12	8 (1.6)	8	2 (25.0)	6 (75.0)
0.25	9 (1.8)	9	8 (88.9)	1 (11.1)
0.5	42 (8.6)	42	41 (97.6)	1 (2.4)
1	46 (9.4)	46	44 (95.7)	2 (4.3)
2	83 (17.0)	53	53 (100)
4	156 (32.0)	10	10 (100)
8	94 (19.3)	11	11 (100)
16	37 (7.6)	10	10 (100)
32	7 (1.4)	7	7 (100)
>32
Total	487	201	186	15

^aIsolates characterized by IEF which revealed the BRO-1 or BRO-2 profile.