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6 D.M. Bryce et al. RESULTS AND DISCUSSION MICROBIOLOGY Antibacterial Activity The bacteriostatic activity of Bronopol in comparison with that of a range of other agents has been determined by serial dilution in 'Oxoid' nutrient agar (see Tables I and II). Plates were inoculated with a multi-point inoculator (13). The bacteriostatic activity against some pseudomonads, including Ps. aeruginosa, Ps. fluorescens and pseudomonads isolated from paints, water, cosmetics and unpreserved pharmaceutical formulations has been compared using a similar technique. Of the antibacterial agents compared only Phenylmercuric Nitrate BP and Chlorhexidine Acetate BPC had similar broad-spectrum activity to that of Bronopol (Tables I and II). 2,4,4'-Trichloro-2'-hydroxydiphenyl ether was more active than Bronopol against most of the organisms tested, but this compound was much less active against Ps. aeruginosa. Of the agents tested against pseudomonads only Phenylmercuric Nitrate BP was more active than Bronopol (see Table III). Table 1II. Comparative activity of Bronopol and other agents against Pseudomonas spp. by agar-dilution. Agar plates inoculated with 0.01 ml of 18 h cultures undiluted incubated for 48 h at 32øC No. of No. of strains with m.i.c. (3tg/ml) of: strains Preservative tested 12.5 25 50 100 200 400 400 Bronopol 23 Propyl Hydroxybenzoate BP 23 Methyl Hydroxybenzoate BP 23 Phenoxyethanol BPC 23 Phenylmercuric Nitrate BP 23 Phenylethyl Alcohol BPC 1963 23 Benzalkonium Chloride 23 Chlorocresol BP 23 Chlorbutol BP 23 Chlorhexidine Gluconate 23 Chlorhexidine Acetate BPC 23 6-Acetoxy-2,4-dimethyl-m-dioxane [1] 12 cis-isomer of 1-(3-chloroallyl)-3,5,7-triaza- 1-azonia-adamantane chloride [2] 12 Substituted imidazolidinyl urea cpd. [3] 6 N-Trichloromethylthio-4-cyclohexene-l,2- dicarboximide [4] 12 Zinc salt of 2-mereaptopyridine-l-oxide [5] 12 2,4,4'-Trichloro-2'-hydroxy-diphenyl ether [6] 6 5 18 0 0 0 0 0 0 0 0 0 0 0 23 0 0 0 0 0 0 23 0 0 0 0 0 0 23 19 2 2 0 0 0 0 0 0 0 0 0 0 23 0 0 0 0 0 19 4 0 0 0 0 0 23 0 0 0 0 0 0 0 23 0 0 3 20 0 0 0 0 4 18 1 0 0 0 0 0 0 0 0 0 12 0 0 0 0 5 3 4 0 0 0 0 2 1 3 0 0 0 0 3 2 7 4 1 2 0 2 2 1 0 0 0 0 0 0 6 [1] Giv-Gard DXN. [2] Dowicil 200. [3] Germall 115. [4] Vancide 89 RE. [5] Zinc pyrithione. [6] Irgasan DP 300. The effects of organic matter and some possible antagonists are shown in Table IV. Bryce and Smart (14) reported that nonionic surface active agents, e.g. polysorbate 80 and lecithin, have little or no effect on the antibacterial activity of Bronopol, although