EFFECTS OF BLOOD MEDIUM SUPPLEMENTS ON ACTIVITIES OF NEWER CEPHALOSPORINS TESTED AGAINST ENTEROCOCCI

This comparative study determined the effect of blood on the antienter ococcal activities of the newer cephalosporins. Standardized disk diff usion susceptibility tests were performed with 57 strains of enterococ ci (30 Enterococcus faecalis strains) on Mueller-Hinton agar with and without 5% sheep blood supplementation. Twelve cephalosporins represen ting five different structural groups (based on the 7-alpha position s ubstitution) were tested. The greatest frequency of activity enhanceme nt by blood was observed with cefdaloxime and cefdinir (7-alpha hydrox yimino group) against E. faecalis. Cephalosporins with a 7-alpha metho xyimino group (cefpodoxime, cefepime, and cefpirome) had marked increa ses in zone diameters (3 to >9 mm) when tested with the blood suppleme nt. Cephems with 7-alpha amino or carboxy substitutions did not demons trate any enhanced activity. Awareness of this phenomenon is important for the interpretation and accuracy of cephalosporin susceptibility t esting.