Effectiveness of Ampicillin Against Gram-Negative Bacteria

Three hundred gram-negative bacteria consisting of approximately 50 strains each ofEscherichia coli, Proteus mirabilis, Klebsiella-Aerobacter, paracolon sp, indol-fermenting strains ofProteus, andPseudomonas aeruginosawere tested against a new penicillin, alpha amino benzyl penicillin (ampicillin) in vitro. The drug showed excellent activity againstE coli- andP mirabilisbut was less effective against the other organisms than agents already available. There was good correlation between results of sensitivity tests performed by the tube dilution and single disc techniques. Forty patients with urinary tract infections were treated with 2 to 3 gm per day of ampicillin for two weeks. In general,E coliinfections were most amenable to therapy and patients with acute uncomplicated pyelonephritis responded better than patients with chronic bacteriuria. Diarrhea occurred in six patients and was the only bothersome side effect associated with ampicillin.