False sensitivity of Enterococcus faecium to amoxicillin-clavulanic acid with the MicroScan system
Joyanes, P.; Pascual, A.; Suárez, A.I.; Martínez-Martínez, L.
Enfermedades Infecciosas y Microbiologia Clinica 13(2): 96-98
1995
ISSN/ISBN: 0213-005X PMID: 7711133 Document Number: 445177
We have observed by using MicroScan automatic system discrepancies in susceptibility results of Enterococcus faecium strains to ampicillin and amoxicillin/clavulanic acid. Seventy-six strains of E. faecium were studied with MicroScan; 98.7% of them were inhibited by 16 mg/l of amoxycillin-clavulanic acid versus 60.5% inhibited by the same concentration of ampicillin. We have evaluated the susceptibility to ampicillin, amoxicillin and amoxicillin-clavulanic acid of 7 strains of E. faecium by both MicroScan and standard microdilution assay. MIC values of ampicillin were similar by both methods but MIC values of amoxicillin/clavulanic acid obtained by MicroScan (< or = 4/2 mg/l in 6 strains) were considerably lower than those obtained by standard microdilution (> or = 16/8 in 6 strains). This phenomenon was not dependent of betalactamase production or bacterial inocula. When using MicroScan, E. faecium strains resistant to ampicillin (betalactamase non producers) must be also considered resistant to amoxicillin/clavulanic acid without considering the values obtained by this system.