<p>The sulfonamides are bacteriostatic agents and the spectrum of activity is similar for all. Sulfonamides inhibit bacterial synthesis of dihydrofolic acid by preventing the condensation of the pteridine with aminobenzoic acid through competitive inhibition of the enzyme dihydropteroate synthetase. Resistant strains have altered dihydropteroate synthetase with reduced affinity for sulfonamides or produce increased quantities of aminobenzoic acid.<br />
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Topically applied sulfonamides are considered active against susceptible strains of the following common bacterial eye pathogens: Escherichia coli, Staphylococcus aureus, Streptococcus pneumoniae, Streptococcus (viridans group), Haemophilus influenzae, Klebsiella species, and Enterobacter species.<br />
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Topically applied sulfonamides do not provide adequate coverage against Neisseria species, Serratia marcescens and Pseudomonas aeruginosa. A significant percentage of staphylococcal isolates are completely resistant to sulfa drugs.</p>