High-level aminoglycoside resistance among enterococci: evaluation of an agar screen susceptibility test.

Seventy-five enterococci from infected (63 isolates) and colonized (12 isolates) patients hospitalized in various divisions of the Policlinico Umberto I, University of Rome, were in vitro studied for high-level resistance (HLR) to gentamicin (HLRG) and streptomycin (HLRS) with adoption of a standard broth dilution and an agar screen test. The employed procedures provided equal results for 100% of the 75 isolates. Of these, 21 (28%) showed HLRG and 43 (57%) HLRS. Combined HLRG and HLRS were found in 18 (24%) isolates, whereas HLRS or HLRG alone were found in 25 (33%) and 3 (4%) isolates respectively. It is concluded that HLR to aminoglycosides may represent a major problem in Italian institutions. Along with other established procedures, the agar screen test employed in the study may be used to detect this antibiotic resistance in enterococci.