Sanitizer efficacy towards attached bacteria

Pseudomonas fluorescens, Yersinia enterocolitica, and Listeria monocytogenes readily attach to both rubber and teflon surfaces. Once attached, a glycocalyx covering forms effectively protecting them from any sanitizer that passes over the surface. Therefore, sanitizers efficacy testing done in the laboratory with pure glycocalyx-free cultures could lead to false assumptions as to the sanitizer's true effectiveness under actual use conditions. Our objectives in this study were: (1) evaluate sanitizer efficacy of in use concentrations toward bacteria attached to gasket materials, (2) examine attachment on rubber versus teflon gaskets, (3) examine different methods of enumeration, (4) compare kill of attached bacteria to suspension tests, (5) determine the minimum inhibitory concentrations of Sanitizers. Iodophor, hypochlorite, acid anionic, peroxyacetic acid, fatty acid and QUAT sanitizers failed to provide an adequate log kill of bacteria attached in levels of 10⁴ to 10⁵. Most of the tests showed that the log kill falls well short of a 3 log reduction goal. Plate counts, impedance microbiology, and the direct epifluorescent filter technique were tested as methods of enumeration. Impedance microbiology was the best method of enumeration, since it allows the estimation of both reversibly and irreversibly attached bacteria. Minimum inhibitory concentration tests demonstrated the increased resistance of attached bacteria as compared to cell suspensions.