POTENTIATION OF PRESERVATIVE EFFICIENCY IN OPHTHALMIC PREPARATIONS

Abstract

SUMMARY Thirty five strains ofPs. aeruginosa isolated from urine and sputum and forty strains ofStaph. aureus collected from urine samples and wound swabs were tested for their native resistance towards the preservatives commonly used in ophthalmic preparations. Out of these isolates, ten strains showing the highest resistance for each ofPs. aeruginosa and Staph. aereus were selected. Five preservatives were tested for their bacteriostatic and bactericidal activities against the ten isolated strains as well as a standard strain for each of Ps. aeruginosa and Staph. aureus. The five tested preservatives were : benzalkonium chloride (BZ), phenyl mercuric acetate (PMA), methyl paraben (MP), phenethyl alcohol (PEA) and chlorbutol (CHB). The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of each preservative towards the tested strains ofPs. aeruginosa and Staph. aureus were estimated by the serial broth dilution and subculture technique, respectively. BZ and PMA were the most active compounds as indicated by the low WC and MBC values obtained. MP was the next preservative having an average MIC value of 1800 µg/ml. The MIC and MBC values ofPEA were higher for Staph. aureus as compared to Ps. aeruginosa indicating higher activity of this preservative towards the Gram-negative organisms. The variation in the MIC and MBC values of CHB was little with an average MIC of 3600 µg/ml and an average MBC of 6300 µg/ml.