THE EFFECT OF SUCROSE LAURATE AND PROPYL 4-HYDROXY-BENZOATE COMBINATIONS ON MICROBIAL-GROWTH .1. GROWTH OF ESCHERICHIA-COLI AND STAPHYLOCOCCUS-AUREUS IN TRYPTICASE SOYA BROTH (TSB) MEDIUM

The use of sucrose laurate (SL) as solubilizing agent for propyl 4-hyd roxybenzoate (PPHB) was investigated, and the antimicrobial effects of SL and of SL/PPHB combinations on the growth of Escherichia coli (Gra m -) and Staphylococcus aureus (Gram +) in trypticase soya broth were studied. Growth of E. coli was not affected at low and intermediate co ncentrations of SL. At concentrations of 5% and higher, a small antimi crobial effect was observed. Staph. aureus. on the contrary, was very susceptible to even small amounts of SL. Differences in susceptibility of E. coli and Staph. aureus could be explained by the protective eff ect of the lipopolysaccharide layer of the gram-negative cell wall. Th e antimicrobial effect of PPHB against E. coli was reduced by the addi tion of SL. The antimicrobial effects of SL and of PPHB against Staph. aureus were almost additive. The synergistic effect of SL and PPHB wa s explained by the increased permeability of the cellular membrane to PPHB. The differences in sensitivity between E. coli and Staph. aureus to SL/PPHB combinations could also be traced back to the lipopolysacc haride layer. As compared to the PPHB solution, the SL/PPHB combinatio n appeared to be more appropriate against Staph. aureus but less appro priate against E. coli.