Sanitizer efficacy against bacteria attached to synthetic meat processing surfaces
The effectiveness of selected sanitizers against bacteria attached to synthetic meat processing surfaces was determined. In initial experiments, in vitro suspensions of Shw. putrefaciens, P. fragi, S. typhimurium, and L. monocytogenes were challenged with sanitizers according to the AOAC Germicidal and Detergent Sanitizer Test (GDST). Germicides employed were chlorine (200 ppm), iodophor (25 ppm), quaternary ammonium compound and phosphoric acid (200 ppm), and peracetic acid (185 ppm). In subsequent studies, the same sanitizers were tested against bacteria attached to polyvinyl chloride, polyurethane, and high density polyethylene surfaces. Test surfaces in sterile poultry slurries were inoculated with bacterial cultures, agitated (100 rpm) for 2 hr at 18°C, and then incubated for 22-28 hr at 26°C (Shw. putrefaciens and P. fragi) or 37°C (S. typhimurium and L. monocytogenes). Scanning electron microscopy (SEM) was employed to determine microbial-surface interactions. Attached organisms remaining on surfaces after vortexing were challenged with germicides. In some cases, surfaces were treated with detergents before applying Sanitizers. Impedance microbiology was used to estimate surviving bacterial populations remaining after chemical treatments. All test sanitizers reduced levels of suspended bacterial cultures >5 logs after 30 sec, and thus, were deemed acceptable according to GDST guidelines. From SEM micrographs, the 22-28 hr surface biofilms of Shw. putrefaciens, S. typhimurium, and L. monocytogenes could be characterized as single adherent cells or cell monolayers. Conversely, the P. fragi biofilm occurred as cell aggregates or microcolonies. Although sanitizers were effective according to GDST results, in many instances, attachment to surfaces increased bacterial resistance to germicidal agents (a 5 log reduction was not observed even after 1 min of chemical exposure). Peracetic acid, overall, was the most effective sanitizer in reducing levels of attached bacteria. Where resistance to other germicides could be observed for up to 20 min, peracetic acid typically eliminated biofilm populations after 1 min. Treatment of surfaces with detergents and then sanitizers led to more effective reductions of attached bacteria. The extensive fibril production by attached S. typhimurium (versus other attached organisms in this research) may explain the greater overall sanitizer resistance of this organism as compared to other test bacteria. However, higher initial numbers of surface bacteria (time 0) may have been the reason for greater sanitizer resistance (higher survivor levels) in some experiments. It is hoped that results of this study can aid processors in developing sanitizer schemes to minimize processing surface contamination with organisms of quality and safety concern.