Survival of Staphylococcus aureus and Escherichia coli as affected by ethanol and NaCl

Growth of three strains of Staphylococcus aureus and two strains of Escherichia coli on nutrient agar (NA) supplemented with ethanol and NaCl was investigated. S. aureus did not grow on NA containing greater than or equal to 10% ethanol (wt/wt) combined with greater than or equal to0% NaCl (wt/wt), or 7.5% ethanol combined with 7.5% NaCl. Neither E. coli nor E. coli O157:H7 grew on NA containing greater than or equal to7.5% ethanol combined with greater than or equal to0% NaCl, 5% ethanol combined with 82.5% NaCl, or greater than or equal to5% NaCl combined with greater than or equal to2.5% ethanol. It is apparent that NaCl enhanced the inhibitory effect of ethanol on growth of S. aureus and E. coli. When cells were suspended in nutrient broth containing 12.5, 20, or 40% ethanol combined with NaCl, viable cells decreased with an increase of ethanol concentration. Ethanol sensitivity among strains and between genera varied in a limited range. When the cells were exposed to 20% ethanol in combination with 5% NaCl, S. aureus and E. coli lost viability after 30 and 10 min, respectively. When treated with 40% ethanol combined with greater than or equal to0% NaCl, all test strains lost viability within 5 min.