Table 3.

Distribution of minimum inhibitory concentrations among Mannheimia haemolytica isolates (n = 219 animals, 233 samples: lung samples = 208, nasal swabs = 16, pleural fluid = 7, heart = 1, joint fluid = 1).

					Distribution (%) of MICs (μg/mL)
Class	Categorya	Antimicrobial	MIC 50	%Rb	≤0.12	0.25	0.5	1	2	4	8	16	32	64
Aminoglycoside	II	GEN	4	3.4c				4.3	38.6	50.6	3.0	3.4
	II	NEO	8	49.4c						13.7	36.9	1.3	48.1
	III	SPE	32	4.3							1.7	20.2	73.0	64 = 0.9 >64 = 4.3
Fluorquinolone	I	ENRO	0.12	3.0	94	1.3	1.3	0.4	3.0
	I	DANO	0.12	3.9c	91	4.3	0.9	3.9
Macrolide	II	TYLT	32	99.1c						0.4	0.4	4.3	94.8
	II	TUL	16	37.8				4.3	6.9	14.6	17.6	14.2	4.7	37.8
	II	TIL	16	44.2						34.8	8.6	12.4	5.6	38.6
B lactams	I	XNL	0.25	0.9		96.6	0.4	1.7	0.4		0.9
	II	PEN	0.12	7.2	51.9	36.5	4.3	1.7	0.4	0.4	4.7
	II	AMP	0.25	5.1c		92.3	1.3	1.3	0.9	0.4	0.4	3.4
Lincosamides	II	CLIN	8	77.7c		0.9		0.9	2.1	18.5	57.5	20.2
Phenicol	III	FFN	1	4.3		1.7	39.9	51.1	2.1	0.9	4.3
Tetracycline	III	OXY	8	53.6			20.6	20.6	4.3	0.9	53.6
	III	CTET	2	11.2			8.2	30.0	25.8	24.9	11.2
Pleuromutilin	III	TIA	16	19.7c				0.4	1.7	3.9	9.4	64.8	19.7

Trimethoprim sulpha^c (Category II): <2/38 = 98.3%, >2/38 = 1.7%.

Sulphahdimethoxine^c (Category III): <256 = 44.6%, >256 = 55.4%.

GEN, gentamycin/NEO, neomycin/SPE, spectinomycin; DAN, danofloxacin/ENRO, enrofloxacin; TYLT, tylosin/TUL, tulathromycin/TIL, tilmicosin; PEN, penicillin/AMP, ampicillin/XNL, ceftiofur; CLI, clindamycin; FFN, florfenicol; SXT, trimethoprim sulpha/SDM, sulphadimethoxine; OXY, oxytetracycline; CTET, chlortetracycline; TIA, tiamulin.

^aCategorization of antimicrobial drugs based on importance in human medicine—Veterinary Drug Directorate.

^bPathogen minimum inhibitory concentration breakpoints from CLSI standards.

^cNo CLSI breakpoint for this bovine respiratory disease pathogen/antimicrobial combination, simply notes susceptibility.

Values in red indicate resistant proportion of samples.

Shaded areas indicate concentrations not tested.