Efficacy of novel organic acid and hypochlorite treatments for eliminatingEscherichia coli O157 : H7 from alfalfa seeds prior to sprouting

This study investigated novel two-step organic acid/hypochlorite treatments as alternatives to 20 000 ppm active chlorine (from calcium hypochlorite) for eliminating Escherichia coli O157:H7 from alfalfa seeds prior to sprout ing. Commercially available alfalfa seeds were inoculated with a five-strai n E. coli O157:H7 mixture and dried to attain ca. 10(6) CFU/g of seeds. See ds then underwent one of several soak treatments including: (1) 5% (v/v) la ctic acid for 10 min at 42 degrees C; (2) 5% acetic acid (v/v) for 10 min a t 42 degrees C; (3) 2.5% lactic acid for 10 min at 42 degrees C followed by 2000 ppm active chlorine (from calcium hypochlorite) for 15 min at 25 degr ees C; (4) 5% lactic acid for 10 min at 42 degrees C followed by 2000 ppm a ctive chlorine for 15 min at 25 degrees C; or (5) 20 000 ppm active chlorin e for 15 min at 25 degrees C. Each treatment reduced numbers of inoculum ce lls by about 6.0 log(10) CFU/g as determined by plating on Sorbitol MacConk ey agar (SMac). Plating on non-selective brain heart infusion agar (BHI) sh owed that treatments 1-4 reduced counts by 2.3-4.1 log(10) CFU/g, thus indi cating a large proportion of injured cells. Successive lactic acid and hypo chlorite treatments (3 and 4) were more lethal than either organic acid alo ne (1 and 2). No surviving cells were detected on SMac or BHI following tre atment with 20 000 ppm active chlorine (treatment 5). Regardless of the pre vious treatment, E. coli O157:H7 counts increased to 10(7)-10(8) CFU/g duri ng sprouting. Germination of seeds was not adversely affected by any of the treatments (germination >90%). Results of this study show that: (a) non-le thal cell injury must be considered when evaluating intervention treatments against E. coli O157:H7 on alfalfa seeds; (b) reductions of 2-4 log(10) CF U/g can be attained without using 20 000 ppm active chlorine; (c) successiv e lactic acid and hypochlorite treatments have greater lethality than organ ic acid treatments alone; and (d) none of the treatments tested can prevent regrowth of surviving E. coli OI57:H7 during sprouting. (C) 2000 Elsevier Science B.V. All rights reserved.