Table 6. Frequency (%) of Streptococcus agalactiae isolates (n = 86) belonging to RAPD-clusters (Ia [n = 35], Ib [n = 32], and II [n = 19]) that had 50% (MIC₅₀) and 90% (MIC₉₀) of bacterial growth inhibited at each antimicrobial concentration.

All isolates were identified from clinical mastitis cases occurred in 9 dairy herds of Southeast, Brazil.

Antimicrobial	Cluster	Frequency (%) of isolates at each indicated MIC (μg/mL)1												NI2	MIC503	MIC904
		0.12	0.25	0.5	1	2	4	8	16	32	64	128	256
Penic+Novob.	Ia	-	-	-	100	0.0	0.0	0.0	-	-	-	-	-	-	1.0	1.0
	Ib	-	-	-	100	0.0	0.0	0.0	-	-	-	-	-	-	1.0	1.0
	II	-	-	-	100	0.0	0.0	0.0	-	-	-	-	-	-	1.0	1.0
Penicillin	Ia	94.3	5.7	0.0	0.0	0.0	0.0	0.0	-	-	-	-	-	-	0.12	0.12
	Ib	100	0.0	0.0	0.0	0.0	0.0	0.0	-	-	-	-	-	-	0.12	0.12
	II	100	0.0	0.0	0.0	0.0	0.0	0.0	-	-	-	-	-	-	0.12	0.12
Pirlimycin	Ia	-	-	100	0.0	0.0	0.0	-	-	-	-	-	-	-	0.5	0.5
	Ib	-	-	53.2	3.1	0.0	3.1	-	-	-	-	-	-	40.6	0.5	>4
	II	-	-	100	0.0	0.0	0.0	-	-	-	-	-	-	-	0.5	0.5
Sulfadimet.	Ia	-	-	-	-	-	-	-	-	17.1	34.3	37.1	8.6	2.9	64	256
	Ib	-	-	-	-	-	-	-	-	34.3	56.3	6.3	3.1	-	64	64
	II	-	-	-	-	-	-	-	-	10.6	52.6	26.3	10.5	-	64	256
Tetracycline	Ia	-	-	-	17.1	8.6	0.0	2.9	-	-	-	-	-	71.4	>8	>8
	Ib	-	-	-	3.1	3.1	3.1	0.0	-	-	-	-	-	90.6	>8	>8
	II	-	-	-	63.2	21.1	5.3	0.0	-	-	-	-	-	10.5	1.0	>8

¹The light gray shading represents the susceptible zone, and the darker gray shading represents the resistant zone. Results were interpreted according to the Clinical and Laboratory Standards Institute (CLSI, [28, 29]). Interpretative criteria were based on human data (ampicillin, erythromycin, oxacillin, penicillin, sulfadimethoxine and tetracycline), dogs’ data (cephalothin), and bovine mastitis (ceftiofur, penicillin/novobiocin and pirlimycin). The resistant category included those isolates categorized as either intermediate or resistant.

²NI = Not inhibited (growth at highest concentration tested).

³MIC (μg/mL) that inhibited 50% (MIC₅₀) of the isolates.

⁴MIC (μg/mL) that inhibited 90% (MIC₉₀) of the isolates.