When Lund and Tybring first described the properties of mecillinam in 1972 they pointed out that this compound differed from known P-lactam antibiotics in two main respects, (i) Mecillinam was highly active against certain Gram-negative bacteria but had much reduced activity against Gram-positive bacteria, unlike penicillins and cephalosporins
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D. S. Reeves (1977) studied this question.