Iron-deficient medium for selective isolation and presumptive identification of enterococci

An Enterococcus Selective Agar (ESA; basal medium plus 0.01% NaN3, pH 9.6, Fe ion-restricted) was applied to a direct, single-step, isolation and presumptive identification of enterococci from clinical urine. The ESA was examined as to rate of colony formation and selectivity together with two conventional culture media, Pfizer Selective Enterococcus Agar (PSE) and Phenyl Ethyl Alcohol Agar (PEA). Significant differences were observed in the rate of colony formation after 14, 17, and 20 hr of incubation at 35 degrees. The size of colonies on ESA was consistently larger than on the other two media. Biochemical testing showed that isolates from ESA conformed more closely to the definition of enterococci than isolates from either PSE or PEA. The improved selectivity of ESA was in large part due to the reduced presence of Fe ions. The medium offers advantages for an expeditious and accurate isolation of enterococcal pathogens.