The role of lipid in the protection of bacteria to phenols in mixed culture



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Mixed culture studies indicate that the sensitivity of Staphylococcus aureus to several phenolic inhibitors can be influenced by the presence of a gram-negative organism. In most instances the presence of P. mirabilis, S. schottmuelleri, or A. aerogenes increased the resistance of the Staphylococci to these inhibitors while in other cases these organisms caused Staph, aureus to be more sensitive. Differential growth rates were responsible for increased sensitivity in mixed culture. It was demonstrated that these gram-negative organisms protected Staph, aureus from 2,4,6-trichlorophenol in a non-nutritive sodium borate buffer. All of the bacteria were more sensitive to this phenol in buffer than in nutrient broth. There was a direct correlation between this protective effect and the quantity of lipid extracted from the whole cell and cell wall of these organisms. Those organisms with higher quantities of lipid were killed at lower concentrations of the inhibitor in pure culture and offered more protection to Staph. aureus in the mixed culture. Distribution coefficient studies between trichlorophenol and the lipid of the cells is related to the sensitivity and capacity to protect in a mixed culture situation. Defatted cells did not protect the Staphylococci from the phenol. Hydrogen-bonding between the cells' lipid and the phenolic compound is discussed as a possible mechanism which determines a cell's response to the inhibitor. Infrared spectrophotometric studies indicate that hydrogen-bonding between fatty acids and phenol does occur. Gas-liquid chromatographic analysis of the fatty acid methyl esters from each organism shows that a high percentage of odd-chain and unsaturated fatty acids is directly related to sensitivity and protection.