Bactericidal activity of organic acids in combination with transdermal compounds against Salmonella typhimurium attached to broiler skin

The aim of this research was to determine the bactericidal activity of low levels of organic acids (0.5% and 1%) when combined with various chemical agents (potential transdermal synergists). The skin attachment model (SAM) was used to determine bactericidal activity of treatments against Salmonella typhimurium attached to chicken breast skin. Treatments consisted of the following synergists: no synergist (control), 125 ppm sodium lauryl sulfate (SLS), 2% ethanol (ETOH), 100 ppm sorbitan monolaurate (Span 20), or 15% dimethyl sulfoxide (DMSO), in combination with acetic, citric, lactic, malic, and tartaric acids at 0.5% (Experiment 1) or 1% (Experiment 2). Treatments were applied during a simulated chill, post-process dip, or scald. The synergists alone were tested and had no bactericidal activity. Addition of ETOH to all organic acids (0.5%) did not increase their activity, and in some cases reduced activity. Addition of SLS to lactic acid in the chiller increased activity (log(10) cfu skin(-1)) of the acid against firmly attached cells from 0.16 (control) to 1.29. Addition of DMSO to lactic acid caused a 0.83 log(10) cfu skin(-1) vs. a 0.36 reduction in the lactic acid control. Adding SLS and DMSO to other acids had little or no effect, and in some cases, decreased activity. Span 20 caused the greatest increase in activity. Addition of Span 20 in the scalder increased activity of all acids against loosely attached cells. Reductions in counts increased by 0.81 (acetic acid) to 2.35 (tartaric acid) log(10) cfu skin(-1). Span 20 also increased activity of citric acid against firmly attached cells by 1.63 log(10) cfu skin(-1) in the scalder. When added to 1% concentration of the acids, SLS caused the greatest increase in activity. Against firmly attached cells, addition of SLS increased activity of the acids in the dip by 0.61 and 0.40 when combined with citric and tartaric acids, respectively. Against loosely attached cells, SLS increased activity of tartaric acid in the scalder application by 1.16 log(10) cfu skin(-1). Activity varied among different potential synergists and was dependent on method of application and acid concentration. In some cases, synergists showed greater activity when combined with 0.5% acid than with 1%. In other cases, the addition of a synergist decreased activity of the acid. In cases where the activity of the acid was increased, the resultant activity was greater than the added activity of the synergist and acid alone, indicating a synergistic effect. (C) 1997 Academic Press Limited.