Effects of low-molecular weight alcohols on bacterial viability

Alcohol based solutions are among the most convenient and wide spread aid in the prevention of nosocomial infections. The current study followed the efficacy of several types and isomers of alcohols on different bacterial species. Seven alcohols (ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, tert-butyl alcohol, and ethylene glycol) were used to evaluate their minimal inhibitory and bactericidal effects by microdilution method on bacteria that express many phenotypical characteristics: different cell-wall structure (Gram positive/negative bacteria), capsule production (Klebsiella pneumoniae), antibiotic resistance (MRSA vs MSSA) or high environmental adaptability (Pseudomonas aeruginosa). Results: The best inhibitory effect was noticed for n-propyl, followed by iso-propyl, n-butyl, and iso-butyl alcohols with equal values. Ethylene glycol was the most inefficient alcohol on all bacteria. In K. pneumoniae and P. aeruginosa, the bactericidal concentrations were higher than the inhibitory one, and to a level similar to that encountered for most of the Gram-positive bacteria. Among Gram-positive cocci, E. faecalis presented the lowest susceptibility to alcohols. Conclusions: All alcohols presented good effect on bacteria, even in low concentrations. Compared to ethanol as standard, there are better alternatives that can be used as antimicrobials, namely longer-chain alcohols such as propyl or butyric alcohols and their iso- isomers. Ethylene glycol should be avoided, due to its toxicity hazard and low antimicrobial efficacy. Bacterial phenotype (highly adaptable bacteria, biofilm formation) and structure (cell wall structure, presence of capsule) may drastically affect the responsiveness to the antimicrobial activity of alcohols, leading to higher bactericidal than inhibitory concentrations.