Sanitizer efficacy against attached bacteria in a milk biofilm

Pseudomonas fluorescens, Yersinia enterocolitica, and Listeria monocytogenes were shown to readily attach to both rubber and Teflon surfaces. Sanitizer efficacy testing done in the laboratory with nonadherent bacteria could lead to false assumptions as to the sanitizer's true effectiveness under processing conditions where cells may be attached. The objectives in this study were: (a) evaluate the efficacy of in-use concentrations of sanitizers on bacteria attached to gasket materials, (b) compare bacterial attachment to rubber and Teflon gaskets, (c) examine different methods of enumeration, and (d) compare sanitizer efficacy on attached and suspended bacteria. The goal reduction for all of the sanitizers tested was greater than or equal to 3 log cycles or 99.9%. Results indicated that iodophor, hypochlorite, acid anionic, peroxyacetic acid, fatty acid, and quaternary ammonium sanitizers failed to provide an adequate reduction in the numbers of attached bacteria at levels of 10(4) to 10(5)/mm2 in most cases. The test organisms attached in slightly higher numbers to the rubber surface versus Teflon. 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 allowed the estimation of both reversibly and irreversibly attached bacteria. The efficacy of sanitizers versus a bacterial suspensions resulted in a greater than or equal to 5 log-cycle reduction. The same concentrations were relatively ineffective against the attached bacteria. The goal reduction was reached on the Teflon surface with the iodophor, hypochlorite, and fatty acid sanitizers with a log-cycle reduction in the number of Yersinia enterocolitica of 3.09, 3.19, and 3.31, respectively. Pseudomonas fluorescens was reduced by 3.16 on both the rubber and Teflon surfaces when exposed to the hypochlorite sanitizer.