Heterogeneous vancomycin-intermediate susceptibility in a community-associated methicillin-resistant Staphylococcus aureus epidemic clone, in a case of Infective Endocarditis in Argentina

Table 1 Susceptibility of urine-(SaU) isolate and blood isolates obtained before (SaB1) and during (SaB2) vancomycin therapy

Isolates	Broth dilution μg/ml		Agar dilution μg/ml		*E-test* μg/ml		VITEK 2 μg/ml		MET μg/ml		GRD *strip* μg/ml		MHA5T
	VAN	TEIC	VAN	TEIC	VAN	TEIC	VAN	TEIC	VAN	TEIC	VAN 24 h/48 h	TEIC 24 h/48 h	TEIC
SaU	1	1	1	1	1	1	1	≤ 05	4	8	1/1	2/2	-
SaB1	1 (1)*	1	1	1	1 (1.5)*	1 (1)*	1	≤ 05	4	8	1/1	2/2	-
SaB2	2 (2)*	4	2	4	2 (2)*	2 (1.5)*	2	4	12	12	4/4	12/16	+

MIC: Minimum inhibitory concentration, VAN: vancomycin, TEIC: teicoplanin, MET: Macromethod E-test, 200 μl of inoculum at 2 McFarland standard suspensions onto BHI Agar, positive result: VAN MIC of ≥8 and TEIC MIC of ≥8 μg/ml or TEIC MIC of ≥12 μg/ml; GRD strip, Etest Glycopeptide-resistance (AB bioMérieux) detection strip were used as described by the manufacture:GRD positive (GISA o h-GISA): VAN o TEIC ≥ 8 μg/ml; MHA5T screening, Mueller Hinton Agar with 5 μg/ml of TEIC, 10 μl of inoculum at 0.5 McFarland-standard direct-colony suspensions. Any growth was considered positive. All screening methods were read at 24 and 48 h and incubated at 35°C. (MIC)*: MIC results from the Instituto Nacional de Enfermedades Infecciosas Dr. Carlos G. Malbran. The strains h-VISA-Mu3 and VISA-Mu50 and the vancomycin-susceptible S. aureus strain ATCC 29213 were tested for all methods in parallel, as positive and negative controls, respectively.

ISSN: 1476-0711