[Experimental study on synergism between cefotaxime and ampicillin against Streptococcus D group]

Cefotaxime (CTX) disks and ampicillin (ABPC) disks exhibited synergism against 24 strains of Streptococcus D group isolated from various sources in our hospital. We were interested in these synergism effects and compared them with the combination index. Twenty-two out of the 24 strains examined exhibited synergism, and were identified as Streptococcus faecalis by the API strep system. We divided them into 4 groups (combination index: 19, 15, 11, 9) according to the degree of synergism. Another 2 strains showed additive effects (combination index: 1), and were identified as Streptococcus faecium. Among these 24 strains, beta-lactamases were produced by only 1. There was no direct connection between beta-lactamase production and synergism. The mechanism of synergism between CTX and ABPC has not yet been studied.