The invention provides compounds and salts of Formula I and Formula II: which possess antimicrobial activity. The invention also provides novel synthetic intermediates useful in making compounds of Formula I and Formula II. The variables A1, R2, R3, R5, R6, R7, A8 and R9 are defined herein. Certain compounds of Formula I and Formula II disclosed herein are potent and selective inhibitors of bacterial DNA synthesis and bacterial replication. The invention also provides antimicrobial compositions, including pharmaceutical compositions, containing one or more compounds of Formula I or Formula II and one or more carriers, excipients, or diluents. Such compositions may contain a compound of Formula I or Formula II as the only active agent or may contain a combination of a compound of Formula I or Formula II and one or more other active agents. The invention also provides methods for treating microbial infections in animals.