Antimicrobial Susceptibility of Udder Pathogens Isolated from Dairy Herds in the West Littoral Region of Uruguay

Table 1 In vitro susceptibility of 336 strains of Staphylococcus aureus obtained from clinical and sub-clinical bovine mastitis cases from the West Littoral Region of Uruguay.

	MIC¹ (μg/ml)				% Resistance
Antimicrobial Agent	MIC₅₀²	MIC₉₀³	Range	Breakpoint	VETMIC	Agar disk diffusion test
Penicillin	0.5	> 8	0.12–> 8	≥ 0.25	47.6	46.1 ⁵
Ampicillin	0.5	8	≤ 0.12–> 16	≤ 0.5	46.7	46.6 ⁵
Oxacillin	≤ 0.5	≤ 0.5	≤ 0.5–1	≥ 4	0.0	2.0 ^{5 6}
Cephalotin	≤ 4	≤ 4	≤ 4	≤ 32	0.0	0.0
Gentamicin	≤ 1	≤ 1	≤ 1–4	≥ 16	0.0	0.0
Erythromycin	≤ 0.5	≤ 0.5	≤ 0.5–> 4	≥ 8	3.0	2.6 ⁵
Oxitetracycline	2	> 64	≤ 0.25–> 64	≥ 16	13.4	14.0 ^{5 7}
Enrofloxacin	≤ 0.25	≤ 0.25	≤ 0.25–0.5	≥ 2	0.0	0.0
Neomycin	≤ 1	≤ 1	≤ 1–64	≥ 64	0.6	0.9 ⁵
Clindamycin	≤ 1	≤ 1	≤ 1	≥ 4	0.0	....⁴....
Amoxicillin/Clavulanic acid	....⁴....	....⁴....	....⁴....	....⁴....	....⁴....	0.0
Trimethoprim/
Sulfamethox.	0.25	0.5	< 0.06–8	≥ 4	0.3	0.0 ⁵

¹ Minimum inhibitory concentration. ² Lowest concentration inhibiting 50% of the isolated tested.
³ Lowest concentration inhibiting 90% of the isolated tested. ⁴ Test not performed.
⁵ No significant differences between methods. ⁶ All strains were sensitive at the confirmation test.
⁷ Tetracycline disk were used to perform agar disks diffusion.

ISSN: 1751-0147