[False sensitivity of Enterococcus faecium to amoxicillin-clavulanic acid with the MicroScan system].
BACKGROUND
We have observed by using MicroScan automatic system discrepancies in susceptibility results of Enterococcus faecium strains to ampicillin and amoxicillin/clavulanic acid.


RESULTS
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.


CONCLUSIONS
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.
Joyanes
P
P
Departamento de Microbiología, Hospital Universitario Virgen Macarena, Sevilla.
Pascual
A
A
Suárez
A I
AI
Martínez-Martínez
L
L
D000658:Amoxicillin / Q000494:pharmacology; D019980:Amoxicillin-Potassium Clavulanate Combination; D001426:Bacterial Proteins / Q000096:biosynthesis; D002969:Clavulanic Acids / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004352:Drug Resistance, Microbial; D016984:Enterococcus faecium / Q000187:drug effects* / Q000201:enzymology; D005189:False Positive Reactions; D016908:Gram-Positive Bacterial Infections / Q000382:microbiology; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000295:instrumentation; D012189:Retrospective Studies; D001618:beta-Lactamases / Q000096:biosynthesis
D001426:Bacterial Proteins; D002969:Clavulanic Acids; D019980:Amoxicillin-Potassium Clavulanate Combination; D000658:Amoxicillin; D001618:beta-Lactamases
Falsa sensibilidad de Enterococcus faecium a amoxicilina-ácido clavulánico con el sistema MicroScan.